INTELLIGENT TEXTILES FOR PERSONAL PROTECTION AND SAFETY
NATO Security through Science Series This Series presents the results of scientific meetings supported under the NATO Programme for Security through Science (STS). Meetings supported by the NATO STS Programme are in security-related priority areas of Defence Against Terrorism or Countering Other Threats to Security. The types of meeting supported are generally “Advanced Study Institutes” and “Advanced Research Workshops”. The NATO STS Series collects together the results of these meetings. The meetings are co-organized by scientists from NATO countries and scientists from NATO’s “Partner” or “Mediterranean Dialogue” countries. The observations and recommendations made at the meetings, as well as the contents of the volumes in the Series, reflect those of participants and contributors only; they should not necessarily be regarded as reflecting NATO views or policy. Advanced Study Institutes (ASI) are high-level tutorial courses to convey the latest developments in a subject to an advanced-level audience Advanced Research Workshops (ARW) are expert meetings where an intense but informal exchange of views at the frontiers of a subject aims at identifying directions for future action Following a transformation of the programme in 2004 the Series has been re-named and reorganised. Recent volumes on topics not related to security, which result from meetings supported under the programme earlier, may be found in the NATO Science Series. The Series is published by IOS Press, Amsterdam, and Springer Science and Business Media, Dordrecht, in conjunction with the NATO Public Diplomacy Division. Sub-Series A. B. C. D. E.
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Sub-Series D: Information and Communication Security – Vol. 3
ISSN: 1574-5589
Intelligent Textiles for Personal Protection and Safety
Edited by
Sundaresan Jayaraman Georgia Institute of Technology, USA
Paul Kiekens Ghent University, Belgium
and
Ana Marija Grancaric University of Zagreb, Croatia
Amsterdam • Berlin • Oxford • Tokyo • Washington, DC Published in cooperation with NATO Public Diplomacy Division
Proceedings of the NATO Advanced Research Workshop on Intelligent Textiles for Personal Protection and Safety Zadar, Croatia 7–10 September 2005
© 2006 IOS Press. All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without prior written permission from the publisher. ISBN 1-58603-599-1 Library of Congress Control Number: 2006922867 Publisher IOS Press Nieuwe Hemweg 6B 1013 BG Amsterdam Netherlands fax: +31 20 687 0019 e-mail:
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Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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Preface Terrorism has become an integral part of everyday life in recent years and has dramatically affected the quality of life for individuals in society. Technology is the key to combating terrorism and protecting ordinary citizens, first responders and soldiers, among others, from danger. The area of intelligent or smart textiles is a rather new but rapidly emerging discipline with a high potential for payoff in the fight against terrorism. This Advanced Research Workshop (ARW) was organized to fill the critical need to bring together the leading experts in the field to make an in-depth assessment of existing knowledge in the area of intelligent (smart) textiles for personal protection and safety, and to identify directions for future research. An important outcome or “deliverable” of the Workshop has been the “Research Roadmap” for the future in keeping with NATO’s goals for the ARW program. This first-of-its-kind ARW in this field also provided a forum for young scientists and engineers to interact closely with the invited experts and participate in developing the Research Roadmap that is expected to advance this emerging discipline through collaborative research between NATO and Partner countries. This book contains the papers presented by the Invited Speakers at the ARW. Each chapter in the book provides an in-depth assessment of one particular facet of this emerging discipline. The chapters build on each other further reflecting the integrated and interdisciplinary theme underlying the ARW. As Co-Directors, we would like to express our sincere thanks and appreciation to all who contributed to the success of the ARW: to NATO for the generous grant; to the fellow members of the Organizing Committee, viz., Professor Danilo De Rossi of the University of Pisa, Italy, Professor Lieva Van Langenhove of Ghent University, Belgium, and Ms. Sungmee Park of the Georgia Institute of Technology, USA; to Dr. Carla Hertleer of Ghent University, Belgium, for her help during the ARW planning stage; to Ms. Judith Kenis, Ghent University, Belgium, for coordinating the logistics that resulted in a productive and enjoyable ARW; to the Invited Speakers, Participants and Discussion Leaders for providing the stimulating intellectual content of the ARW; again to Ms. Sungmee Park for her extensive help in the preparation of this book for publication; and finally, to the IOS Press staff for their assistance in the timely production of the book. Sundaresan Jayaraman Paul Kiekens Ana Marija Grancaric December 2005
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Contents Preface Sundaresan Jayaraman, Paul Kiekens and Ana Marija Grancaric Advanced Research Workshop on Intelligent Textiles for Personal Protection and Safety Paul Kiekens Intelligent Textiles for Personal Protection and Safety: The Emerging Discipline Sungmee Park and Sundaresan Jayaraman The Wearable Motherboard: The New Class of Adaptive and Responsive Textile Structures Sungmee Park and Sundaresan Jayaraman New Textile Materials for Environmental Protection Izabella Krucińska, Eulalia Klata and Michał Chrzanowski Wearable Mechanosensing and Emerging Technologies in Fabric-Based Actuation Danilo De Rossi, Federico Carpi, Federico Lorussi, E. Pasquale Scilingo and Alessandro Tognetti
v
1 5
21 41
55
Flexible Displays on Textiles for Personal Protection Vladan Koncar and François Boussu
65
Conductivity Based Sensors for Protection and Healthcare Lieva Van Langenhove and Carla Hertleer
89
Optical Chemical Sensors and Personal Protection Aleksandra Lobnik
107
Ergonomics of Protective Clothing; Heat Strain and Fit Hein A.M. Daanen, Peter A. Reffeltrath and Claudy L. Koerhuis
133
Author Index
147
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Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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Advanced Research Workshop on Intelligent Textiles for Personal Protection and Safety Paul KIEKENS Ghent University, Belgium Together with my co-directors Prof. Ana Marija Grancaric from the University of Zagreb and Prof. Sundaresan Jayaraman from Georgia Institute of Technology I would like to welcome you at this unique location for attending the Advanced Research Workshop that is organized with the support of NATO. The WTC attacks in New York on 11 September 2001; the train explosions in Madrid on 11 March 2004, the massacre at the public transport in London on 7 July 2005; these major terrorist assaults are unfortunately engraved in our memories and emphasize the importance and necessity of the fight against terrorism. Thousands of people lost their lives during these assaults, among which mainly civilians but also a great number of fire fighters. Furthermore these attacks put the work of people as fire fighters and first responders in the picture and intensify the extreme conditions under which these people are working. Governments need to deal with finding political solutions to prevent more terrorist attacks, while scientists can contribute to the defence from a technological point of view. Applying intelligent textiles in this battle is an obvious choice. Clothing is a person’s second skin, covering great parts of our body on the one side and having a large surface area in contact with the environment on the other hand. Therefore clothing is most suitable as interface between environment and human body, resulting in the ideal tool to enhance personal protection and provide occupational safety. This idea as such of course is not new; clothing always had a protecting function among other things. All clothing is protective to some extent, while the degree of protection against specific hazards varies according to the area of application. Personal protective equipment (PPE) includes more than just the garments; face masks, gloves, shoes, etc. all take part of the equipment. The nature of the workplace hazards resulted in grouping PPE in categories such as chemical, thermal, mechanical, nuclear and biological. Each category uses its own range of high performance materials with very specific superb properties. Over the years, growing concern regarding health and safety of workers in various sectors of the industry, has led to intensive research and development in the area of personal protective equipment. The quality of PPE has improved as a result of the introduction of specialty fibres, on-going research on polymers, coatings and fabrication techniques. Some major breakthroughs will be mentioned. During
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the nineteen sixties and seventies, Dupont scientists synthesized the aramid fibres Nomex and Kevlar which are known for their excellent thermal resistance. Similar fibres were developed by other companies. Apart from that, many of these fibres have properties such as high tensile strength, high chemical resistance, good structural rigidity, high cut resistance, low thermal shrinkage, excellent dimensional stability,…making them most suitable for use in protective clothing. Since Kevlar has a higher strength than Nomex, Nomex III was developed by blending Nomex with 5% Kevlar to prevent bursting in flame or intense heat. The polyamide-imide fibre Kermel from Rhodia Performance Fibres (F) is lightweight, has a soft handling and a high wicking performance to encourage the outward migration of perspiration away from the body. The Japanese company Toyobo introduced the PBO fibre ZYLON. PBO stands for poly(p-phenylene-2,6-benzobisoxazole), a fibre having a tensile modulus that is greater than carbon, HPPE, or aramid fibre types. Additionally the fibre has a great resistance to heat. As for fabrication techniques, only the 3D weaving process will be mentioned here. Despite its existence since the seventies, it has not been widely used due to the high costs associated with it. In 3D weaving, yarns are not only woven in x and y directions but also in z direction, yielding a three dimensional fabric structure. The way of combining different layers of fabric results in benefits such as a weight reduction of the composite structure, greater impact resistance, no delamination ... Apart from a continuous improvement of material properties and manufacturing processes, new developments are more situated in the area of ergonomics. A better fitting of the clothing considerably contributes to an enhanced performance. One way to do this is to decrease the weight of the apparel by increasing the amount of air trapped within the clothing, using 3D structures instead of 2D. Airlock by Gore tex adopted this concept by integrating air cushions into the fabric. The introduction of adaptive materials such as phase change materials initiated the use of passive smart materials. When integrated at the appropriate places of the garment, they can increase the thermal comfort or reduce the pain alarm time for someone exposed to high temperatures. The properties of the textile materials, the way these materials are combined and assembled resulted in continuously improved garments. However, despite their superior properties, these materials remain mainly passive components. The next level protective clothing can elevate to be the one of an active clothing system. This brings us to the concept of smart clothing. Integrating sensors, actuators, power supplies and microsystems into clothing creates a whole new approach of looking at the role of clothing in meeting human needs. Wearable technology can be achieved by combining engineering and clothing design. Textiles provide “large” surface areas and can serve as a viable platform for “hosting” the large numbers of sensors and processors required for such applications. Since clothing is the most "universal of interfaces", intelligent or smart textiles will serve as the platform for achieving the goals of personal protection and security for individuals against various forms of terrorism. The area of smart textiles is a rather new but rapidly emerging discipline with a high potential for payoff in the fight against terrorism. However the development of intelligent textile systems requires an intensive multidisciplinary interaction, joining the expertise of material scientists, physicians, engineers, etc. Research is being carried out in this area in several parts of the world. Unfortunately, so far there is no concerted effort to drive the research in the direction of fighting terrorism using this emerging technology. Therefore, there is a need to bring together leading experts in this field to make critical
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assessment of existing knowledge in the area of intelligent textiles for personal protection and safety, and to identify directions for future research in this field. This brings us to the aim of organizing this unique Advanced Workshop. In developing the content of the ARW, the inter- or multi-disciplinary approach has been adopted to the field of intelligent textiles for individual protection and safety, resulting in the following facets or building blocks [BB]: x x
x x
x
x
BB 1 - The Threats: Initially, the various types of threats (chemical, nuclear, biological, etc.) have to be considered in the design of intelligent textiles to enhance personal protection and safety of individuals in the fight against terrorism; BB 2 - Platform: The design of the platform or infrastructure for the sensors/electronics, which involves the exploration of materials, structures and manufacturing associated with the intelligent textiles/clothing for defence against terrorism; BB 3 - Interconnect Architecture: The design and incorporation of physical data paths and interconnection technologies, i.e., the realization of “textile electrical circuits” in the fabric to make them “intelligent”; BB 4 - Hardware Integration: The incorporation in clothing of smart sensors (vital signs, chem.-bio), microchips and other devices (e.g., for communication and control) is critical for the realization of intelligent textiles for any personal protection application against terrorism, say for example first-responders and civilians, battlefield management; BB 5 - Software: Issues related to the processing of information are critical for the incorporation and optimal utilization of computing resources. These issues include fault tolerance in light of manufacturing defects and Quality of Service (QoS) within the intelligent textiles and between the intelligent textile and external agents/devices; BB 6 - Performance Metrics: Successful transformation of the technology of intelligent textiles into the field of defence against terrorism should be driven by a set of performance metrics that could range from the physical dimensions (of the resulting structure/system) to the costs, the manufacturability and the data flow rates. All these elements must be utilized to assess the successful realization, performance and deployment of the desired intelligent textiles at the frontline of defence against terrorism.
These different building blocks constitute the basis of our programme of the coming days. As a result, this workshop aims at creating a ‘Research Roadmap’ in order to direct future research for textile based systems related to personal protection in the fight against terrorism. As mentioned before, an intelligent textile based system for personal protection is the result of multidisciplinary research. Therefore we have brought together leading experts in the field of intelligent and protective textiles, young scientists and engineers and manufacturers of protective clothing, coming from 18 different countries. During the next 4 days all of you will closely collaborate and participate in developing this roadmap. Now what is expected from speakers and participants during the days of this Workshop? As part of the presentation, each expert will identify the key advanced research opportunities in
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his area. During the last hour of each day’s session, a Discussion Leader will facilitate an interactive session amongst all the participants to develop a set of research ideas based on the day’s presentations. The afternoon of the last day of the workshop will entirely be devoted to the development of a “Research Roadmap” by the participants, again facilitated by a Discussion Leader. This Research Roadmap will be one of the key “deliverables” of the ARW. Besides being unique and timely, this Workshop will lay the foundation for exciting research advancements in the future that will contribute to increased personal protection and safety, and aid NATO’s mission of fighting terrorism and enhancing safety and security around the world through technology. Last but not least I particularly would like to thank, in addition to NATO, 1. Zadar City for offering us the concert 2. the University of Zadar for providing the piano for the concert and putting the University Grand Hall at our disposal 3. Zadar County for showing us unforgettable nice places in Zadar city 4. “Maraska” Zadar, for letting us taste a typical Croatian delight 5. Zadar Society for Protecting Cyclists in Traffic, for helping us experience a safe bicycle ride to Zadar Thank you for your attendance and I hope you will all have a great and fruitful stay, here in Zadar.
Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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Intelligent Textiles for Personal Protection and Safety: The Emerging Discipline Sungmee PARK and Sundaresan JAYARAMAN1 Textile Information Systems Research Laboratory Georgia Institute of Technology, Atlanta, Georgia 30332, USA
Abstract Terrorism has become an integral part of everyday life in recent years and has dramatically affected the quality of life for individuals in society. Technology is the key to combating terrorism and protecting ordinary citizens and first responders from danger. Textiles are pervasive and the array of polymers, fibers and manufacturing technologies enable the creation of large shapeconformable surface areas that can serve as viable platforms for sensors – human worn and environmental – to detect, possibly prevent, and protect against the devastating results of acts of terrorism. In this paper, we present a typical “terrorist incident response scenario” and discuss the need for a systems approach to enhancing personal protection and safety. We discuss the various types of threats, identify the types of individual protection needed for the various threats, and discuss the threat-specific parameters that need to be monitored. Finally, we present the need for – and identify unique aspects of – research in the various building blocks of this emerging discipline of intelligent textiles for personal protection and safety. Keywords:
Terrorism, Threat Response and Protection System, Personal Protection, Safety, Wearable, Textiles
Introduction It is hard to place a price tag either on human life or on the quality of life. This has become starkly evident with the terrorist attack on the Twin Towers at the World Trade Center on September 11, 2001 in New York, and the most recent attacks in London on July 7, 2005. A new “normal” has emerged for people around the world and terrorism appears to have become an integral part of the fabric of everyday life – an unfortunate reality. Technology is the key to defense against any form of terrorism and for enhancing the safety and quality of life for everyone – from ordinary citizens to first responders attending to disaster victims. Unfortunately, casualties are associated with protection of 1
To whom correspondence should be addressed (
[email protected]).
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innocent citizens and preservation of national security – be they soldiers on the battlefield or first responders saving the lives of innocent victims subjected to terrorist attacks. This is because in a disaster-type situation, the lethal elements (e.g., gas) will take the same time to reach the unprotected potential victims as they would to reach detection sensors. Consider a typical incident response scenario shown in Figure 1: When the first responders receive an alarm or alert to a terrorist incident, they must respond efficiently and reach the disaster scene as quickly as possible. The next step is the detection and identification of the threat – explosive, chemical, biological, nuclear, etc. – and this should be carried out accurately and reliably. Analysis of the threat species needs to be thorough resulting in the reliable diagnosis and effective treatment of the individuals. Containing the threat and limiting its spread are critical to minimizing casualties. Following treatment, the individuals (and the environment) must be decontaminated effectively and thoroughly with no residue on the individuals leaving the scene. Restoration of order (to the extent possible) is the final step in the incident response scenario. One of the keys to a successful response is the preparation for such an event, which includes adequate resources of trained personnel and state-of-the-art equipment, a reliable and efficient communication system, all of which are backed by an effective logistics system. In Figure 1, the events are shown on the left and the corresponding performance metrics are shown on the right. Respond to Alarm or Terrorist Incident
Time (Speed) and Efficiency
Detect and Identify Threat Agent
Accuracy and Reliability
Diagnose and Treat Individuals
Reliability and Effectiveness
Contain Threat
Degree of Localization (Area)
Decontaminate Individual / Environment
Effectiveness and Residue
Restore Order
Time Lapse and Degree of Restoration
Preparation: Training and Infrastructure Resources: Rescue Personnel, Equipment Communications System Logistics System
Figure 1. A Typical Incident Response Scenario: Events and Metrics Analysis of Incident Response Scenario: Need for a Multifaceted Solution: In analyzing the events associated with the incident response scenario, it is clear that the first responders should – in a very short period of time – go into “high-risk” environments about which there is no a priori knowledge, viz., the type of threat or extent of damage. Moreover, these individuals act as information nodes gathering valuable situational awareness information from the “field” and communicating it to
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the “command center” where that information is transformed into knowledge so that a suitable response might be initiated. The individual, in essence, is a “sensor” in this network that is collecting and processing information in real-time. Lack of proper and timely information, and hence knowledge, about the highly dynamic environment is hazardous to these individuals who need to operate in them. As shown in Figure 2, knowledge is essential for the safety of the personnel and success of the mission.
Information
Knowledge
S5
Information
Knowledge
Strength
Speed
Safety
Survival
Success Anyone
Anywhere
Figure 2. The I-K-S5 Framework
Therefore, the solution to protect individuals and enhance their safety should encompass the following key facets: 1. Advance awareness, i.e., sense and extract the information from the dynamic disaster environment in real-time so that the humans and/or robots entering the domain can adapt by being prepared and respond appropriately, thereby minimizing risks to themselves. 2. The protection and safety of the individual first responders on the scene involved in helping the disaster victims. 3. The rapid deployment of measures to minimize casualties and losses on the scene and contain the threat. This multifaceted solution is critical for enhancing the protection and safety of individuals affected by and/or working in disaster scenes.
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The unique characteristics of textiles render them a viable platform for “hosting” large numbers of sensors and processors required for achieving the goals of personal protection and security for individuals against different forms of terrorism. Therefore there is a need to explore the emerging discipline of intelligent textiles for personal protection and safety. The remainder of the paper is organized as follows: In Section 1, the major types of threats are discussed; in Section 2, the types of protection needed to respond to the various threats are presented along with the parameters that need to be monitored. The major components of the threat response system are discussed in Section 3. Unique aspects of research in intelligent textiles for personal protection and safety are presented in Section 4 followed by concluding remarks in Section 5.
1. Analysis of Major Threats An understanding of the major types of threats is the critical first step in developing systems for providing protection and enhancing safety of individuals and other targets in the disaster scene. There are four major types of weapons or instruments that terrorists can use to cause harm and destruction [1, 2]. These are: (i) conventional; (ii) nuclear; (iii) biological; and (iv) chemical. As shown in Figure 1, the best step for protection against any threat is preparation – accomplished through training and a robust infrastructure. Table 1 presents the key characteristics of the four major types of threats. Conventional Weapons are typically explosives that are launched as bombs; the attacks on September 11, 2001 in New York were unique in that aircraft were used as weapons for the first time. When conventional weapons are used, damage to individuals occurs through dust and shrapnel caused by debris and falling objects. One of the collateral damages can occur from asbestos in old buildings. The damage can be detected almost immediately and the explosive generally causes structural damage leading to the collapse of the structure. It is relatively easy to launch a conventional weapons attack as was evident during the Oklahoma City bombing. The duration of the risk from the damage tends to be short-term. The containment of the threat is relatively easy since the threat area is generally localized.
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Table 1. Characteristics of Major Types of Threats Conventional
Nuclear
Biological
Launch Mechanism
Explosive, Missile (Aircraft)
Radioactive Bombs
Pathogens and Toxins
Damage Occurs Through
Dust, Shrapnel
Breathing and Skin Exposure
Skin, Breathing and Ingestion
Detection Time
Immediate
Immediate
Damage Type
Structural
Ease of Launching Risk Duration Containment Potential Targets
Easy
Radiation: alpha, beta and gamma rays Difficult
Immediate and/or Delayed Diseases (smallpox, pneumonia) Medium
Chemical Nerve, Blister, Blood, Choking and Incapacitating Agents Skin, Eye, Ingestion and Injection (Shrapnel) Immediate
Chemical
Medium
Short-Term
Short- and Short- and Short- and Long-Term Long-Term Long-Term Easy Difficult Difficult Difficult Buildings, HVAC Systems, Bridges, Tunnels, Mass Transit, Water Distribution Systems, Public Places (Sports Stadiums), etc.
Nuclear Weapons are radioactive bombs; damage to individuals occurs through breathing and skin exposure to the dust contaminated with radioactive materials. Radiation in the form of alpha, beta and gamma rays can have both short- and longterm impact on the individuals and the environment. Since all the three forms of radiation are odorless and colorless, they can be detected only with radioactive detectors, but the detection itself can be immediate. The containment of the threat would also be difficult; however, it is difficult to launch a nuclear weapons attack since access to radioactive materials and such weapons is not easy. Biological Weapons are pathogens and toxins. The former are disease-causing organisms, some of which can reproduce and cause damage long after the attack. Pathogens can be bacteria such as anthrax, viruses such as smallpox and dengue fever, and microplasms that can cause pneumonia. Toxins are poisonous substances produced by living things; even small doses of toxins can cause large-scale damage to lives. Potential toxin weapons include ricin and botulism toxin. Toxins are also considered to be chemical weapons. Biological weapons cause damage through breathing, skin and ingestion and the reaction can be immediate and/or delayed depending on the nature of the weapon. Depending on the weapon, detection can be immediate and/or delayed. The duration of the risk is both short- and long-term as some of the pathogens can
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mutate and cause damage over time. However, launching a biological weapons attack is of medium difficulty because of restricted access to such materials. Containment of the threat would not be easy. Chemical Weapons are chemical agents that can cause different types of damage depending on the particular agent. Nerve agents attack the individual’s nervous system; blister agents attack the skin; blood agents attack the blood and impair its ability to hold and deliver oxygen; choking agents attack the lungs; and incapacitating agents irritate the mucous membranes, eyes, nose and mouth leading to the individual’s incapacitation. These chemicals attack the individual through skin, eyes, ingestion and penetration or injection caused by shrapnel. The detection can be immediate; the duration of the risk from the chemical weapons attack can be both short- and longterm. Launching of a chemical weapons attack is easier than launching a nuclear weapons attack and is of medium difficulty. Since the likely method of delivery of chemical agents is in the form of gas, which can spread quickly and widely, containment of the threat due to a chemical weapons attack can be difficult. In today’s environment, virtually anything that is unprotected is a target for attacks. Terrorists, however, seek to afflict the maximum damage, both physical and psychological; consequently, certain targets such as buildings, HVAC (heating, ventilation and air-conditioning systems), bridges, tunnels, mass transit, water distribution systems and public gathering places (sports stadiums) become more attractive; at the same time, these entities are likely to be guarded and better prepared for such attacks rendering them less vulnerable in practice. We will now examine the types of protection needed to enhance the safety and security of individuals that might have to deal with the consequences of the four major types of threats. 2.
Analysis of Types of Protection
The key and common impact of all the threats is clear: damage to people, property and possibly, the environment. In devising a solution to enhance protection and safety, a two-step process should be considered. The first would address the protection required for any type of threat and the second step would be the threat-specific protection. By adopting this modular approach to the design of threat protection systems, it will be easier to develop additional solutions for newer classes of threats as they unfold. Facets of Protection: The design of the solution should be guided by the following key factors associated with threat protection, viz., identify, locate, track and monitor the well-being of the individual at all times; minimize time of exposure to the hazard, keep distance from the hazard, and provide complete barrier protection from the hazard. Based on the analysis presented earlier in Table 1, it is clear that the hazard can cause harm to the individual through the skin, by inhalation, by ingestion and penetration through shrapnel or debris. Therefore, threat protection for the individual should consider the key facets shown in Figure 3.
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Physiological
11
Vital Signs Chemical
Respiratory Radiation
Eyes Fire
Penetration
Chemical
Radiation
Barrier Skin
Figure 3. Facets of Personal Protection against Threats It is critical to keep track of the rescue personnel at all times. In such high-stress situations and in their efforts to save lives, the personnel may be oblivious to their own physical condition and well-being. It is estimated that heart attacks – attributed to overexertion and stress – are the leading cause of on-duty fatalities for U.S. firefighters. Therefore, it is important to have location sensors on the personnel and their movements should be continuously monitored. Simultaneously, their vital signs such as heart rate, respiration rate, electrocardiogram and body temperature must be monitored away from the disaster/rescue scene; at the sign of any significant change in their vital signs, they must be evacuated to avoid any mishaps and fatalities. According to estimates, over 80% of firefighters’ injuries and 50% of line-of-duty deaths are due to smoke exposures, consisting of carbon monoxides and other chemicals. Therefore, respiratory protection is extremely critical for rescue personnel; in addition to protection against such noxious gases, special filters to guard against other hazards such as radioactive dust must be provided. Barrier protection – for the eyes and skin – is critical. Any unprotected part of the body, however tiny, becomes an entry point for the hazard compromising the individual’s safety. In designing and developing barrier protection solutions it is important to consider the three primary modes in which the barrier may be broken; these include abrasion, cuts from sharp edges (e.g., knives, shrapnel), and chemical. Also, no barrier will remain impervious to a specific chemical forever nor is any material resistant to all chemicals [3]. Materials will have different permeation rates and so some chemicals may travel through or permeate the material in a few seconds, while others may take longer – days or weeks. Permeation rate is defined as the rate at which the chemical will move through the material and it is different from penetration; the latter occurs when the chemical or hazard leaks through the material – through seams, pinholes and other defects. The breakthrough time is the time it takes a
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chemical to permeate completely through the material and provides an indication of how long the material can provide barrier protection before the chemical permeates through the material. Degradation is a measurement of the physical deterioration of the material due to contact with a chemical. The material may get harder, stiffer, more brittle, softer, weaker or may swell. The worst example is that the material may actually dissolve in the chemical [3]. Finally, the rescue personnel must be monitored for any psychological breakdown caused by the intensity of the trauma; typically, this type of trauma occurs post facto and the evaluation must be carried after the incident. Simultaneously, the physiological well-being of the individual must be monitored to ensure that there are no long-term effects due to any exposure to the hazardous environment during the rescue. Classes of Personnel: Yet another dimension to the design of protection systems (apart from the general and threat-specific protection) is the class of personnel for whom the system is being designed. Typically, individual protection and safety are important for first responders (firefighters and medics), hazmat personnel, public safety personnel, soldiers and industrial workers. For instance, the medic at the disaster scene may not come in contact with the fire hazard and may not require fire protection that the firefighters may need. Likewise, for public safety personnel such as police officers, protection against knives and bullets may be critical, something that may not be needed for the medics. We will now discuss the key components of an effective threat response and protection system. 3.
Threat Response and Protection System
The key components of an effective threat response and protection system are: x An Advanced Awareness System x An Individual Protection and Safety System x A Collective Protection and Threat Containment System. These three components cover the three phases associated with dealing with any threat – before, during and after an attack – discussed in Section 1. Advance Awareness System (AAS): The Advance Awareness System must, at a very minimum, carry out three key functions: (i) acquire environmental data about the disaster scene; (ii) process the data locally on the scene; and (iii) transmit it to the humans/robots approaching the scene and also to the command, control and communications center (C4). That information will be utilized away from the scene by the approaching humans and/or robots (Hn), and C4 to develop and/or suitably modify the response (see Figure 4).
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Figure 4. Advance Awareness System for a Disaster Scene The first step in acquiring environmental data involves the deployment of sensors (Sn) in the affected area. The uncertainty of where a disaster might occur poses interesting challenges. On one hand, it is conceivable to integrate sensors into public places such as office buildings, sports stadiums, airports, mass transit stations and the like as part of the standard fixtures such as fire sprinklers and climate control systems. However, the process and resources required for selecting and deploying the right type of sensors and their continuous maintenance to “terror-proof” such structures will be considerable and potentially render this opportunity difficult to realize in practice. Therefore, the scene assessment must occur post facto, i.e., after the disaster has struck and ideally before the first responders arrive at the scene. The sensors should be of different types (nuclear, chem., bio, temperature, etc.) and several of the same type may be needed to cover the environment for obtaining reliable ambient intelligence, and any potential dangers. Moreover, the sensors should be inexpensive because they are likely to be damaged in the environment, which also points to the need for redundancy. Low cost sensors would also mean minimal processing capabilities and preferably low power requirements. Since the information needs to be transmitted longer distances from the scene, these sensors must communicate with a multifunction processor/controller that is deployed with them. Finally, the system must be easily
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deployable on any terrain and must conform to the shape or structure of the terrain. One potential way of deployment is for the soldiers/rescue personnel to “shoot” the sensors from a distance and have it land on the scene. Individual Protection and Safety System (IPSS): Based on the analysis in Section 1, it is clear that the individual protection and safety system requires a sensor network that can be worn comfortably by the rescue personnel. In addition to protection, the solution should maintain (or enhance) the comfort level of the individual; this means human factors and ergonomics should be considered in the design of the system. For example, keeping a firefighter comfortable (during exposure to burning flames) by regulating the temperature in the suit is critical during a firefighting operation. As in the case of AAS, the individual protection and safety system must accommodate a wide array of sensors in varying numbers and meet the other criteria of low cost, low power and communications capabilities. Collective Protection and Threat Containment System (CPTCS): A collective protection and threat containment system will protect civilians in the disaster scene and contain the threat so that casualties are minimized. Physically, the structure should be rapidly deployable and over different areas and terrains [4]. They should also accommodate a wide array of sensors and warning systems to ensure the safety of the environment. A decontamination unit may be attached to the CPTCS to decontaminate individuals. Need for a Textile-Based Infrastructure: Based on the preceding requirements associated with deploying sensors, it is clear that there is a need for a “platform” or “infrastructure” for the three components, viz., AAS, IPSS and CPTCS, respectively, that: 1. Can be shaped and sized to meet the requirements of the 1.1. Individuals, viz., soldiers and first responders at the scene; and 1.2. Deployment environment and terrain; 2. Can be preconfigured and also rapidly reconfigured on the fly with the desired suite of heterogeneous sensors and multifunction processors integrated into the substrate; 3. Is robust and durable to withstand different types of operational (stress/strain) and harsh environmental (biohazards and climatic) conditions; 4. Is lightweight, portable and easy to deploy in the scene; 5. Is easy to decontaminate; 6. Is wearable, comfortable, customizable and launderable; and 7. Is easy to manufacture and has low cost. A textile or fabric-based substrate would meet these requirements because fabrics [5]: 1. Are flexible, strong, lightweight, and shape conformable; 2. Can be made in desired dimensions of length and width, and hence area; 3. Can be engineered from a variety of fibers and yarns using various manufacturing processes to accommodate different types of operational and environmental conditions; 4. Are easy to manufacture in a relatively cost-effective (inexpensive) manner compared to traditional printed circuit boards; and 5. Can easily accommodate “redundancies” in the system.
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The influence of key design parameters on the properties of the resulting textile structures is captured in Table 2. Therefore, textiles can serve as the informationcarrying infrastructure or platform for AAS, IPSS and CTCSS. Table 2. Design Parameters and Properties of Textile Structures [6] Increase Only
Tensile Initial Tearing Bending Air-Per Abrasion Shear Flexural Thickness Strength Modulus Strength Stiffness meability Resistance Resistance Endurance
Fiber Linear Density (Cross-Sectional Area) Yarn Linear Density
Yarn Twist
Threads/inch Interlacings per Unit Area (Weave Pattern)
Need for a Systems Approach to Threat Response and Protection System: The key operations associated with threat response and protection are shown in Figure 5. These are Sense, Process, Diagnose and Treat; any solution should incorporate the enablers for carrying out these operations. As shown in Figure 5, the primary enablers are Sensors, Threat Analysis System, Communication System and Treatment Support System. There is a critical need for adopting the systems approach in designing the solution because each of these components must seamlessly integrate with one another to achieve the desired goal of protection and safety for individuals. Note that the other elements of the threat response scenario discussed in Section 1 are not shown in the figure, but are assumed to be an integral part of the solution. The sensors in the environment or on the individual detect the ambient conditions in the disaster scene and the situational data is analyzed by the Threat Analysis System to determine the type of threat. Among the capabilities of the TAS is the ability to process the vital signs signals from the individual in real-time. Moreover, with the widespread availability of mobile phones (which come equipped with a radio mechanism and increasingly include GPS capabilities), they could become a “platform” for TAS. The Communications System is responsible for providing the infrastructure for communication during the rescue operation (at the scene, with remote locations, etc.) and the mobile phone could be part of this infrastructure. Finally, the Treatment Support System with a built-in decision support system utilizes the threat analysis information to select and implement a suitable treatment regimen and minimize injuries and casualties at the disaster scene.
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Sense
Sensors
Treat
Treatment Support System
Individual
Threat Analysis System
Process
Communications System
Diagnose
Figure 5. Primary Operations in Threat Response and Protection: A Systems View
Thus, by integrating the technology enablers of sensors, processors (computing, communications, drug delivery, etc.) into the fabric substrate, the traditionally passive textiles can be transformed into interactive textiles or i-Textiles; this, together with the communications infrastructure (satellite, wireless, etc.) and back-end data management and decision support module, results in an Interactive Textile-based Information Processing System (ITIPS), which can serve as an effective and innovative platform and enhance the protection, safety and quality of life for individuals involved in rescuing and providing security – in disaster scenes resulting from terrorist acts and on the battlefield (Figure 4). Moreover, the ITIPS modules can be deployed in other environments such as office buildings, homes, hospitals and fields as shown in Figure 6 thus providing ubiquitous monitoring. Thus, the emerging discipline of intelligent textiles can facilitate the concept of cost-effective protection and safety anytime, anywhere for anyone.
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Figure 6. Ubiquitous Monitoring with ITIPS Modules: Anytime, Anywhere, Anyone
We will now examine the unique aspects of research in this emerging discipline of intelligent textiles for personal protection and safety.
4.
Unique Aspects of Research
The primary components of the threat response and protection system represent the building blocks of this emerging discipline of intelligent textiles for personal protection and safety, and present unique and challenging opportunities for research. This is shown in Figure 7.
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Sensors
Fabric Infrastructure
Integration
Treatment Support System
Threat Analysis System
Figure 7. Building Blocks of Research for Threat Response and Protection System One of the key themes of the research must be the pursuit of seamless integration of the various building blocks. For example, while the capabilities and functionalities of sensors are critical to meet the various threats, their form factor is very important so that they can be easily integrated into the fabric infrastructure. Similarly, research on the fabric infrastructure should address the important aspect of sensor integration so that sensors of different types and varying (small to large) numbers can be easily “plugged in and out” to meet the rapidly-changing requirements of different types of threats identified in Section 2. Another important aspect of research associated with fabric infrastructure is the need for large-scale interconnections to route information to the large numbers of sensors integrated into the fabric. These will be in addition to the typical research in this area to develop new fibers, fabrics, three-dimensional structures, and finishes for meeting specific performance requirements. The real-time routing of information between the various sensors in the fabric and to a common data collection point for threat analysis opens up interesting opportunities for research; for example, the development of an intelligent controller for the “in-fabric network” that can also communicate with the backend processing and threat analysis system. Likewise, in the area of treatment support, MEMS-based technologies for the delivery of the antidotes and drugs to treat the victims open up interesting and novel avenues for exciting research. This research calls for interdisciplinary teams of experts from the fields of materials science, textile engineering, electrical engineering, computing, communications and specific application domains of military, medicine and first responders. The successful transformation of this technology of intelligent textiles into the field for the fight against terrorism should be driven by a set of performance metrics that could range from the physical dimensions (of the resulting
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structure) to the costs, the manufacturability and the efficacy of the threat response and protection system. The other Chapters in this book and the roadmap emerging from this NATO Advanced Research Workshop highlight the specific opportunities for research in this emerging discipline of intelligent textiles for personal protection and safety. 5.
Concluding Remarks
Protection against the devastating impact of terrorism is critical for ensuring an individual’s safety and security in today’s dynamic world, especially those involved in rescue operations. By virtue of its unique features, textiles provides an excellent platform for the incorporation of sensors and processors that can add intelligence to the normally passive, yet shape-conformable structures. Threat response and protection requires a systems-based multifaceted approach and should address advance awareness, individual protection and safety, and collective protection and threat containment, respectively. An Interactive Textile-based Information Processing System (ITIPS) can serve as an effective and innovative platform to enhance the protection, safety and quality of life for individuals involved in rescuing and providing security. There are many unique aspects of research associated with this emerging discipline of intelligent textiles that can lead to the realization of cost-effective protection and safety anytime, anywhere for anyone. References [1] [2] [3] [4] [5] [6]
Topfer, Hans-Joaschim, Nuclear Biological Chemical (NBC) Defence Pocket Handbook, Alfred Karcher GmbH &Co., Winnenden, Germany, March 2000. Heyer, R.J., Introduction to NBC Terrorism, #20, DERA Monograph Series, The Defense Preparedness and Emergency Response Association, Longmont, CO, USA, October 15, 2001. Chemical Protective Clothing – Glove Selection, Canadian Center for Occupational Health and Safety, www.ccohs.ca, Last Accessed: August 2005. Verge, A.S., “Rapidly Deployable Structures in Collective Protection Systems”, Soldier Biological Chemical Command, Natick, MA. Park, S., and Jayaraman, S., “Smart Textiles: Wearable Electronic Systems”, MRS Bulletin, August 2003, pp.586-591. Newsletter, Albany International Research Company, Dedham, MA, USA.
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Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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The Wearable Motherboard: The New Class of Adaptive and Responsive Textile Structures Sungmee PARK and Sundaresan JAYARAMAN1 Textile Information Systems Research Laboratory Georgia Institute of Technology, Atlanta, Georgia 30332, USA
Abstract. Sensors are pervasive – from homes to battlefields, and everywhere in-between. They are facilitating information processing anytime, anywhere for anyone. Likewise, textiles are pervasive and span the continuum of life from infants to senior citizens. The invention of the Jacquard weaving machine led to the concept of a stored “program” and “mechanized” binary information processing. This development served as the inspiration for Charles Babbage’s Analytical Engine – the precursor to the modern day computer, which has since spawned the growth of sensor networks in recent years. In this paper, we explore the potential synergy between sensor networks and textiles, and identify the need to bring about a seamless “integration” between the two domains. We then present the i-Textiles (Interactive Textiles) paradigm and its role in realizing this type of integration for creating a technological solution to enhance individual protection and safety. We discuss the design of the Wearable Motherboard in the context of sensor networks. Finally, we present an overview of the major applications of i-Textiles-based sensor networks and conclude the paper with a look at the future of the paradigm of “fabric is the computer.” Keywords: Wearable Motherboard, Intelligent Textiles, Smart Shirt, Sensor Network
Introduction Sensors are pervasive – from homes to battlefields, and everywhere in-between. Examples include microwave ovens, mobile phones, automobiles, and medical equipment. They have become such an “integral” part of our daily lives that they are not only pervasive but they are also “invisible” to the end-user. For example, the microwave-user interface is so simple that with the touch of a few buttons a different “programming” sequence can be launched by anyone – from a young kid to a senior citizen – for a wide variety of tasks, viz., from reheating a cup of coffee to preparing an entire meal. This type of transparency of user interface coupled with the invisibility of the “embedded” technology in the various devices
1
To whom correspondence should be addressed “
[email protected]”.
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and systems has contributed to their explosive growth and proliferation. These systems are facilitating information processing anytime, anywhere for anyone. While these types of sensors and networks incorporating such sensors are relatively new in the timeline of civilization, there has been one piece of “sensing” technology that has been there since the dawn of civilization. And that is textiles, which, in today’s world are indeed pervasive. Textiles (clothing) were initially used for “protection” from the environment – be it from climatic conditions or from other predators as camouflage and personal privacy. This first dimension of “protection” has been complemented by the second dimension of “aesthetics,” exemplified by the success of fashion houses in modern times – from Armani to Versace. Humans are used to wearing clothes from the day they are born and, in general, no special ‘training’ is required to wear them, i.e., to use the interface. In fact, it is one that can be ‘tailored’ to fit the user’s needs, moods and desires while accommodating the constraints imposed by the ambient environment in which the user interacts with the interface, i.e., different climates, activities, budgets and occasions. In other words, a garment is probably the most universal of interfaces and is one that humans need, use, have familiarity with, enjoy, and which can be easily customized [1]. This “universal interface” of clothing is in contrast to typical computer interfaces/systems (e.g., Linux, Unix, Windows, Mac-OS) each of which has some unique characteristics and requires time and effort to learn to use. Moreover, textiles are pervasive: They span the continuum of life from infants to senior citizens, and from functionality (astronaut’s space suits) to fashion (evening dress); they can be found in everyday clothing to specialized applications such as geotextiles to prevent soil erosion at the beaches. Thus, they provide an excellent platform for the incorporation of sensors to create sensor networks and embedded systems.
1. Meeting the User’s Demands: Need for Convergence Today’s individual is extremely active – or dynamic – and is demanding. The explosion of technology – electronics, computing and communications in the form of sensors and embedded systems – has fueled this demanding nature of the individual seeking connectivity and interactivity with surrounding objects and the environment. So, the ‘ultimate’ information processing system for this demanding user should not only provide for large bandwidths, but also have the ability to sense, feel, think, and act. In other words, the system should be totally ‘customizable’ and be ‘in-sync’ with the human. Human as an Information Node: In today’s urban warfare, the soldier acts as the “information node” gathering valuable information from the “field” and communicating it to the command center where that information is transformed into “knowledge” so that the mission (and hence the soldier) is safe and successful. The soldier, in essence, is a “sensor” in this sensor network that is collecting and processing information in real-time. In a similar scenario of responding to a terrorist attack, the first responders themselves become “information nodes” in a human ad hoc network and provide valuable information from the disaster scene to the situation command center established a little distance from the scene.
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Thus, in both examples, humans themselves become another type of “sensor” in the realtime network and their care, safety and protection in these stressful situations become important. Need for Convergence: Since clothing is pervasive and presents a “universal” interface, it has the potential to meet the emerging needs of today’s dynamic individual, viz., interactivity, connectivity, ease of use and a “natural” interface for information processing. Moreover, an individual is likely to be forgetful and leave a PDA (personal digital assistant) behind, but is unlikely to walk out of the home without clothes! Therefore, there is a critical need to integrate the enabling technologies of electronics, sensors, computing and communications into textiles so that the traditionally passive, yet pervasive, textiles can be transformed into an interactive, intelligent information infrastructure for the demanding end-user to facilitate pervasive and personalized mobile information processing and provide individual protection and safety. Also, textiles provide the ultimate flexibility in system design by virtue of the broad range of fibers, yarns, fabrics, and manufacturing techniques that can be deployed to create products for desired end-use applications. Textiles also provide “large” surface areas that may be needed for “hosting” the large numbers of sensors and processors (the sensor network) that might be needed for deployment over large terrains, e.g., a battlefield or a terrorist disaster scene and for individual protection and safety. The opportunities to build in redundancies for fault tolerance make textiles an “ideal” platform for information processing that is critical for protecting individuals against the results of terrorist acts, which might include nuclear, chemical and biological weapons. The Third Dimension of Intelligence: Textiles can therefore serve as a true informationprocessing infrastructure with the ability to sense, feel, think and act based on the wearer’s stimuli and/or the operational environment in which the textiles are deployed. The “technology enablers” – sensors and sensor networks – can be effectively incorporated into traditional textiles to add the third dimension of intelligence to textiles resulting in the next generation of “Interactive Textiles” or i-Textiles, and pave the way for the paradigm of “fabric is the computer” – the ultimate integration of textiles and information processing or computing. Figure 1 is a conceptual representation of this integration between an exquisite textile fabric and a network of sensors leading to an innovative, intelligent information infrastructure that is customizable, has the typical look and feel of traditional textiles, and can meet the demands of today’s dynamic individual and mission-critical applications.
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Æ
+
Traditional Textiles
Sensors & Sensor Networks
Interactive Textiles
Figure 1. Interactive Textiles (i-Textiles): An Innovative, Intelligent Information Infrastructure
1.1. Non-Traditional Textile Developments In this section, we present an overview of a few recent developments in the area of nontraditional textiles that go beyond the conventional applications of textiles as clothing and furnishing materials. SOFTswitch technology enables textiles to function as interfaces to control electronic devices [2]. The soft flexible touch-sensitive fabrics can be used in place of conventional hard switches, keypads, keyboards, buttons or knobs. The Musical Jacket, developed at the MIT Media Lab from a Levi’s Denim Jacket, incorporates an embroidered fabric keypad, a sewn conducting fabric bus, a battery pack, a pair of commercial speakers and a miniature MIDI synthesizer pin [3]. Post, et al., describe the development of e-broidery or electronic embroidery – the patterning of conductive textiles by numerically controlled sewing or weaving processes – as a means of creating computationally active textiles [4]. In April 2002, Infineon announced a voice-controlled MP3 player that can be sewn directly into shirts or jackets [5]. We will now the present the concept of interactive textiles.
2. The New Class of Interactive Textile Structures The term “E-Textiles” or “Electronic Textiles” is being used to denote the class of structures that integrates electronics elements with textiles [6]. However, the term “ETextiles” doesn’t convey the “interactivity” that is key to the successful development and deployment of such structures. Moreover, the hallmark of sensors and sensor networks is the associated interactivity, which enables them to be pervasive and ubiquitous. Therefore, we propose the term “i-Textiles” to convey this “dynamic” or “interactive” nature of these new structures that goes beyond the passive incorporation of “electronic” elements into textile structures. It is not just the substitution of the word “interactive” for “electronics”,
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rather it is a paradigm shift with regards to these structures that calls for going beyond the simple incorporation of electronic devices on to the fabric – the fabric does indeed become the computer eventually. Although it would require extensive research and development to realize this paradigm in its entirety, it is important to adopt this long-term view and develop the “building blocks” that are critical to this vision [7]. The Vision of i-Textiles Figure 2 depicts our vision for i-Textiles embodying the paradigm of “fabric is the computer.” The various “building blocks” of the system – representing the various facets that must be seamlessly integrated to realize the vision – begin with the underlying physical fabric or “Platform.” The design of this platform or infrastructure involves the exploration of materials, structures and manufacturing technologies.
Platform • Materials • Structure • Manufacturing Methods
Performance Metrics • Dimensions • Data Rates • Fault Tolerance • Cost • Manufacturability • Durability
Interconnect Architecture • Circuit Layout • Interconnection Tech. • Power Distribution
ii--Textiles
Software Runtime • Runtime Internal • Internal External • Ex ternal QoS • QoS
Hardware Integration • Sensors • Devices
Figure 2. The i-Textiles Paradigm The second key facet for realizing this paradigm of a true computational fabric is the “Interconnect Architecture” in the fabric, which involves the design and incorporation of physical data paths and interconnection technologies, i.e., the realization of “textile electrical circuits.” Integration of sensors, microchips and other devices (e.g., for communication and control) is critical for the realization of an “intelligent” i-Textiles for
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any application, say for example, battlefield management, and therefore, “Hardware Integration” constitutes the third facet or building block shown in Figure 2. Issues related to information processing such as fault tolerance in light of manufacturing defects and Quality of Service (QoS) within the i-Textile and between the i-Textile and external agents/devices are critical for the incorporation and optimal utilization of computing resources, and therefore, “Software” is the fourth facet of the i-Textile continuum. And finally, as shown in the figure, a set of underlying performance metrics ranging from the physical dimensions (of the resulting structure/system) to costs, manufacturability and data flow rates must be utilized to assess the successful realization and performance of the desired i-Textile. Thus this paradigm of “fabric is the computer” represents a fascinating area of research that calls for collaboration amongst scientists and engineers from a variety of disciplines including textiles, computing and communications, sensor technologies and application domains. We will now present the Wearable Motherboard paradigm as an effective means of creating sensor networks in textiles.
3.
The Wearable Motherboard: Paradigm, Architecture & Technology
In the spring of 1996, DARPA through the US Department of the Navy, put out a "broad agency announcement" to create a system for the soldier that was capable of alerting the medical triage unit when a soldier was shot, along with some information on the soldier's condition characterizing the extent of injury. It specified the following two key broad objectives for the Sensate Liner: x x
Detect the penetration of a projectile (e.g., bullets and shrapnel); and, Monitor the soldier's vital signs.
Based on the above two key requirements, the first step in the design and development process was to gain an understanding of the user’s needs and carry out user requirements analysis. 3.1 User Requirements Analysis The twin functionality required in the system was analyzed and the fact that a suite of vital signs (e.g., heart rate, respiration rate, electrocardiogram (EKG) and body temperature) had to be monitored led to the following conclusions: 1. 2. 3. 4.
Different types of sensors were needed to monitor the various vital signs. Different numbers of sensors were needed to obtain the signals to compute a single parameter. The sensors needed to be positioned in different locations to acquire the proper signals. Different subsets of sensors may be used at different times necessitating their easy attachment and removal, or plug and play.
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In short, it became clear that what was needed was the design and implementation of a sensor network on the soldier to achieve the desired functionality of penetration sensing and vital signs monitoring. The ideal infrastructure available to create this sensor network was the soldier’s uniform because the clothes were in contact with the soldier’s body, which was the source of signals for the various vital signs. Moreover, the functionality, modularity, flexibility (plug and play) required of the sensor network led to the choice of the motherboard paradigm. Just as special purpose chips and processors can be plugged into a computer motherboard to obtain the desired information processing capability (e.g., high-end graphics), the chosen Motherboard paradigm provides an extremely versatile framework for the incorporation of sensing, monitoring and information processing devices [1]. In addition, the sensor network in the form of the Motherboard had to be wearable and have the look and feel of regular textiles, and thus the paradigm of “Wearable Motherboard” was born. The focus of the work has been on creating a personal wearable information infrastructure that would be comfortable like any garment, rather than just making a computer wearable as in the traditional school of wearable computers [8, 9]. 3.2. The Wearable Motherboard: Design Issues There were two classes of design issues: one related to the realization of a sensor network in a textile structure; and the second related to the information processing facet of the resulting structure. Platform or Infrastructure: Since the objective was to create a comfortable and wearable information infrastructure for the sensor network, the additional user requirements for the Wearable Motherboard were identified based on the two key performance requirements. A detailed and more specific set of performance requirements was defined with the result shown in Figure 3. These requirements are Functionality, Usability in Combat, Wearability, Durability, Manufacturability, Maintainability, Connectability and Affordability. The next step was to examine these requirements in-depth and to identify the key factors associated with each of them. These are also shown in the figure. For example, Functionality implies that the wearable motherboard must be able to detect the penetration of a projectile and should also monitor body vital signs – these are the two requirements identified in the broad agency announcement from the Navy. The factors deemed critical in battlefield conditions are shown under Usability in Combat in the figure. These include providing physiological thermal protection, resistance to petroleum products and EMI (electromagnetic interference), minimizing signature detectability (Thermal, Acoustic, Radar and visual), offering hazard protection while facilitating electrostatic charge decay and being flame- and directed energy retardant. Likewise, as shown in the figure, Wearability implies that the wearable motherboard should be lightweight, breathable, comfortable (form-fitting), easy to wear and take-off, and provide easy access to wounds. These are critical requirements in combat conditions so that the soldier’s performance is not hampered by the protective garment. The durability of the wearable motherboard is another important performance requirement. It should have a wear life of 120 combat days and should withstand repeated flexure and abrasion – both of
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which are characteristic of combat conditions. Manufacturability is another key requirement since the design (garment) should be eventually produced in large quantities over the size range for the soldiers; moreover, it should be compatible with standard issue clothing and equipment. Maintainability is an important requirement for the hygiene of the soldiers in combat conditions; it should withstand field laundering, should dry easily and be easily repairable (for minor damages). The developed solution should be easily connectable to sensors and the Personal Status Monitor (PSM) on the soldier. Finally, affordability of the proposed solution is another major requirement so that the garment can be made widely available to all combat soldiers to help ensure their personal survival, thereby directly contributing to the military mission as force enhancers. GTWM Requirements
Functionality •Projectile Penetration Alert •Monitor Body Vital Signs
Usability in Combat • Physiological Thermal Protection • Minimize Signature Detectability - Thermal, Acoustic, Radar & Visual • Resistance to Petroleum Products • Electrostatic Charge Decay • Resistance to EMI • Hazard Protection - Nuclear, Biological & Chemical • Flame & Directed Energy Retardancy • Biomechanical Efficiency
Wearability
Durability
• Comfortable - No Skin Irritation & No Pressure Points • Breathable (Air Permeable) • Moisture Absorption - Wickability (MVTR) • Lightweight - Low Bulk & Weight • Dimensional Stability • Easy to Wear & Take-off • Adjustable with Standard Handwear • Easy to Access Wounds • Maintain Operational Mobility • Maximize Range of Motion
• Wear Life of 120 Combat Days • Flexural Endurance • Strength - Tear, Tensile & Burst • Abrasion Resistance • Corrosion Resistance
Manufacturability
Maintainability
• Military Size Ranges • Compatible with Standard Combat Clothing and Equipment • Ease of Fabrication
• Field Launderable • Easy Drying • Color Fastness • Repairable • Odor-free and Anti-bacterial
Connectability • To Sensors • To Personal Status Monitor
Figure 3. Performance Requirements for the Wearable Motherboard Thus, in the first step of the conceptual design process, the broad performance requirements were translated into a larger set of clearly defined functions along with the associated factors. The details of the design methodology can be found elsewhere [10]. The initial version of the Wearable Motherboard (Figure 4) was created in the form of an undershirt and it came to be known as the “Smart Shirt” [5]. Additional details of the design framework for can be found in [7]. Information Processing: On the second facet of information processing, the following design issues were addressed:
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1. 2. 3. 4.
29
The signals from the various sensors, and in different locations, had to be sensed, collected, processed, stored, and transmitted to the monitoring station. Signals from multiple sensors of the same type (e.g., EKG) had to be processed to compute a single parameter (EKG waveform). Signals from different types of sensors had to be processed nearly simultaneously to evaluate the parameters. Providing power for the various operations.
20” 1.5” 10”
Electrical Conducting Component Penetration Sensing Component 20” Form Fitting Component Static Dissipating Component Comfort Component
Figure 4. Schematic of the Woven Wearable Motherboard Figure 5 shows the key functional operations associated with the Wearable Motherboard, which are analogous to those in a typical computer; the architecture was designed and developed to realize these functions in the Wearable Motherboard.
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Sensors
Sense
Input
Collect
Move
Process
Compute
Store
Memory
Transmit
Output
Figure 5. The Desired Functionality and Computing Analogy
3.3 The Wearable Motherboard Architecture Figure 6 shows the architecture of the Wearable Motherboard intended for medical and first responder applications. The comfort or base fabric provides the necessary physical infrastructure for the Wearable Motherboard. The base fabric is made from typical textile fibers where the choice of fibers is dictated by the intended application. The developed interconnection technology has been used to create a flexible and wearable framework to plug in sensors for monitoring a variety of vital signs. Just as the motherboard facilitates the “plug and play” concept, other sensors can be easily integrated into the structure. For instance, a sensor to detect oxygen levels or hazardous gases can be integrated into a variation of the Smart Shirt that will be used by first responders responding to terrorist incidents. Similarly, by plugging in a microphone into the Smart Shirt, voice can be recorded.
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S. Park and S. Jayaraman / The Wearable Motherboard Microphone
Sensor
Interconnection Point Data Bus
T -Connectors Basic Grid
Multi -Function Processo
Figure 6. The Wearable Motherboard Architecture The sensors can be positioned in desired locations on the body and will plug into the Smart Shirt. As shown in Figure 6, the signals from the sensors flow through the flexible data bus integrated into the structure to the multifunction processor/controller. This processor/controller, in turn, processes the signals and transmits them wirelessly to desired locations (e.g., doctor’s office, hospital, battlefield triage station). The bus also serves to transmit information to the sensors (and hence, the wearer) from external sources, thus making the Smart Shirt a valuable information infrastructure, especially for enhancing the
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protection and safety of individuals. The multifunction processor/controller provides the required power to the Wearable Motherboard. Thus the Wearable Motherboard paradigm is an effective means of creating sensor networks in textiles, where the resulting structure has the look and feel of traditional textiles with the fabric serving as a comfortable information infrastructure. We will now discuss the salient features of the Smart Shirt. 3.4. The Georgia Tech Wearable Motherboard (Smart Shirt) The Smart Shirt uses optical fibers to detect bullet wounds, and special sensors and interconnects to monitor the body vital signs during combat conditions. However, as the research progressed, new vistas emerged for the deployment of the resulting technology including civilian medical applications and the new paradigm of personalized mobile information processing using the flexible information infrastructure. Several versions of the Smart Shirt have been produced and with each succeeding version, the garment has been continually enhanced from all perspectives – functionality, capabilities, comfort, ease of use and aesthetics. 3.5 Testing of the Smart Shirt The penetration sensing and vital signs monitoring capabilities of the Smart Shirt have been tested. For penetration sensing, a bench-top set-up comprising a low-power laser was used at one end of the plastic optical fiber (POF) to send pulses that 'lit up' the structure indicating that the Wearable Motherboard was armed and ready to detect any interruptions in the light flow that might be caused by a bullet or shrapnel penetrating the garment (Figure 7). At the other end of the POF, a photo-diode connected to a power-measuring device measured the power output from the POF. The penetration of the Smart Shirt resulting in the breakage of POF was simulated by cutting the POF with a pair of scissors; when this happens, the power output at the other end on the measuring device falls to zero. The location of the actual penetration in the POF can be determined by an Optical Time Domain Reflectometer.
0.389 Photocell POF
Panel Mount Display Unit
Light Source
Figure 7. Benchtop Set-Up for Projectile Penetration (POF) Testing of GTWM
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The vital signs monitoring capability has been tested by a subject wearing the garment and measuring the heart rate, respiration rate, electrocardiogram (EKG) and body temperature using commercial off-the-shelf sensors that “plug” into the Smart Shirt. Three EKG sensors were attached to the human subject. The subject put on the Smart Shirt like putting on any undershirt. The sensors on the body were 'plugged' into the T-Connectors on the Smart Shirt worn by the subject. The leads from the EKG monitor were connected to the T-Connectors on the Smart Shirt. Thus, the heart-related signals collected by the sensors on the body passed through the T-Connectors on the Smart Shirt and through the leads at the bottom of the Smart Shirt and into the EKG monitor. Initial testing was done at Crawford Long Hospital in Atlanta followed by another set of tests in the Department of Physiology at Emory University. An infant version of the Smart Shirt was subsequently tested in collaboration with the Egleston Hospital of Emory University School of Medicine. The vital signs data has been wirelessly transmitted to a personal computer. The garment is also comfortable and easy to wear and take-off, similar to a typical undershirt. As shown in the EKG traces in Figure 8, the tests conclusively demonstrated the ability of the Smart Shirt to monitor the vital signs of individuals (from infants to adults) in an easyto-use form factor with the convenience and familiarity associated with a garment.
Top Trace: From the Smart Shirt Bottom Trace: Directly from the User Figure 8. Wireless Transmission of Vital Signs from the Smart Shirt
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3.5.1 Testing Under Extreme Conditions The Smart Shirt was worn by a race car driver in a practice event during the LeMans series on the Daytona 500 track and the driver’s vital signs data (heart rate and EKG) were transmitted wirelessly to the race car pit. This test demonstrated the ability of the Smart Shirt to monitor vital signs under extreme conditions of nearly 2.5G-forces acting on the driver traveling at speeds in excess of 180 miles per hour. 3.5.2 Launderability The Smart Shirt successfully withstood the series of industry-standard launderability tests (washing and drying) typically carried out on textiles and apparel. It functioned effectively after every wash thus demonstrating the robustness of the Wearable Motherboard paradigm embodying the principle of “plug and play” where the sensors and key electronic components are “unplugged” from the Smart Shirt prior to it being laundered.
4.
Applications of the Smart Shirt Technology
This research on the design and development of the Smart Shirt has opened up new frontiers in personalized information processing, healthcare and telemedicine, and space exploration, to name a few [12]. Until now, it has not been possible to create a personal information processor that was customizable, wearable and comfortable; neither has there been a garment that could be used for unobtrusive monitoring of the vital signs of humans on earth or in space. Figure 9 illustrates the use of the Smart Shirt in a variety of applications. The back-end Data Display and Management System – with a built-in knowledge-based decision support system – can receive the vital signs data from multiple users in real-time and provide the right response to the situation [13]. Specifically, the Smart Shirt has the potential to serve as the “platform” for a variety of sensors that might be used for detecting nuclear, biological and chemical contaminations that could occur with terrorist acts.
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First Responder at Site
Smart Shirt: Collects and Moves Data Comfortable, Lightweight Washable, Durable
Child Astronaut in Space
Smart Shirt Controller: Stores and/or Transmits Data Selects Best Transmission Method
Mountain Climber
Race Car Driver
Off-Site Remote Monitoring & Data Management System Data Transport Through Appropriate Communications Infrastructure
Figure 9. Smart Shirt in Various Fields of Application 4.1 Impact of the Smart Shirt Technology: The Value of i-Textiles The Smart Shirt will have a significant impact on the practice of medicine since it fulfills the critical need for a technology that can enhance the quality of life while reducing healthcare costs across the continuum of life, viz., from newborns to senior citizens and across the continuum of medical care, viz., from homes to hospitals and everywhere inbetween. By having a technology that is not only ubiquitous but also has the ability and intelligence to respond to the changes in the needs of the wearer, the quality of preventive care can be significantly enhanced, thus reinforcing the paradigm that “investment in prevention is significantly less than the cost of treatment.” For instance, when an infant version of the Smart Shirt is used for monitoring babies prone to SIDS (sudden infant death syndrome), it can shift the focus from the treatment of infants who have suffered brain damage due to apnea to the prevention of the damage in the first place.
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Likewise, a home setting can contribute to faster recovery. For example, if a patient recovering at home from heart surgery is wearing the Smart Shirt, the vital signs including EKG can be transmitted wirelessly (through a mobile phone, Internet, etc.) to the hospital on a regular basis. This monitoring will help the patient feel more "secure" and will facilitate the recuperation while simultaneously reducing the cost and time associated with recovery. Moreover, in the event of an emergency, the doctor can be notified instantaneously. Using the online medical records (available over the Web), the physician can administer the right treatment at the right time at the right cost, and indeed save a life thereby realizing the full potential of the Smart Shirt technology!
5.
Looking Ahead: Adaptive and Responsive Systems
By providing a “platform” for a suite of sensors that can be utilized to monitor an individual unobtrusively, the Smart Shirt technology opens up exciting opportunities to develop “adaptive and responsive” systems that can “think” and “act” based on the user’s condition, stimuli and environment [14]. Thus, the rich vital signs data stream (and resulting knowledge) from the Smart Shirt can be used to design and implement “realtime” feedback mechanisms to enhance the quality of care for the individual by providing appropriate and timely medical “intervention.” By applying advancements in MEMS (micro-electro mechanical systems) technology, a feedback system – including a drug delivery system – can be integrated into the Smart Shirt to prevent, for instance, fatalities from an anaphylaxis reaction or a diabetes shock.. Of course, mechanisms to guard against inadvertent administration of the drug can be built as part of the control system. Having such a feedback system as an “integral” part of the fabric will represent yet another step towards the realization of the “fabric is the computer” paradigm. 5.1 i-Textiles and Personal Privacy As with any advanced information technology, invasion of personal privacy becomes a very big concern and i-Textiles is no exception. However, since the technology is in the form of a “garment,” the user (or the caregiver, in the event the user is unable to make the choice due to age or mental incapacitation) must make the “deliberate” choice to put on the garment and only then can the data be monitored [15]. In other words, the user has control over personal privacy. Advances in telecommunications technology are addressing other across-the-board issues such as data integrity, data latency, data security and these will not be unique to this use of i-Textiles. The user (i.e., the patient) will have the right to grant access to the appropriate individuals such as physicians, hospitals and insurance companies. The ease with which personal data can be collected in real-time using the Smart Shirt will result in the creation of “knowledge banks” of human performance; this knowledge base can be used in clinical and pharmaceutical research potentially leading to new treatments, drugs and drug delivery systems. These benefits should be weighed in the context of potential invasion of personal privacy.
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5.2 Design of i-Textiles: Challenges and Opportunities The principal advantage of a fabric is its ability to conform to shape and serve as a “platform” or infrastructure to “hold” sensors and other information processing devices over varying surface areas (from small to large). In such a loosely-coupled mode, there is no interaction between the fabric and the electronic elements and the information carrying capabilities of textile fibers are not harnessed. The only advantage of this loose coupling is the ability to quickly deploy sensors and devices over desired areas – akin to rolling out a carpet. However, the communication between the sensors and devices must be accomplished through a wireless network. The opportunity therefore lies in bringing about a true “integration” between the textile elements and the sensors by incorporating the sensors into the fabric so that the communication between the sensors is through the textile fibers. This type of a “tight” coupling will lead to an embedded system similar to the one shown in Figure 1. The power to these embedded devices can be supplied through the fabric, thus minimizing the on-board power requirements for these devices. Although the Wearable Motherboard represents a significant step in realizing true integration between textiles and information processing elements (e.g., sensors, actuators and devices), there are several principal challenges that must be addressed: 1.
2. 3.
Need for real-time routing of information between the various sensors in the fabric: In the event the fibers in the textile-based embedded system are damaged, the “failure” in the network must be recognized and alternate “data paths” must be established in the fabric to maintain the integrity of the sensor network. The creation of an “in-fabric” network with “interconnections on the fly” in the Wearable Motherboard using field programmable gate arrays (FPGAs) has been discussed in [16, 17]. A common interface for sensors to be easily plugged into, and unplugged from, the fabric platform. The T-Connector in the Wearable Motherboard represents a significant first step in realizing this type of a common interface. Market acceptance of such integrated systems: In addition to the key technical challenges, the market acceptance of such textile-based embedded systems must be addressed; this can be done by demonstrating the value of such systems in specific end-use applications such as medical monitoring and firefighting.
6. Concluding Remarks The field of textiles was responsible not only for the first industrial revolution but also for the information processing revolution witnessed in recent years with the invention of the Jacquard weaving machine that served as an inspiration to Charles Babbage for his work on the Analytical Engine. Today it is i-Textiles, which has the potential to bring about yet another transformation in the field of information processing through the effective use and application of sensors and sensor networks in a wide variety of applications. i-Textiles represent a novel and effective information infrastructure that can be tailored to suit the requirements of specific applications. They fulfill the key role of being a
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flexible information infrastructure that will facilitate the paradigm of ubiquitous or pervasive computing. Just as the spreadsheet pioneered the field of information processing that brought “computing to the masses,” it is anticipated that i-Textiles will bring personalized and affordable healthcare monitoring and diagnostics to the population-atlarge thus leading to the realization of “Affordable Healthcare, Anyplace, Anytime, Anyone.” This “fabric is the computer” paradigm demonstrates the feasibility of realizing personalized mobile information processing (PMIP) and sets the stage for transforming information processing in the future.
Acknowledgements: Initial research on the Wearable Motherboard was carried out under Contract # N66001-96-C-8639 from the US Department of Navy. The authors would like to thank Dr. Eric Lind of the US Department of Navy, Mr. Don O'Brien of the U.S. Defense Logistics Agency and Dr. Rick Satava of DARPA for identifying the need for a soldier protection system and for providing the funds to carry out this research. Thanks are due several individuals at Crawford Long Hospital, the Department of Physiology, Emory University School of Medicine, and Children’s Healthcare of Atlanta for their help in testing the Smart Shirt. Dr. Chandramohan Gopalsamy and Dr. Rangaswamy Rajamanickam contributed to the initial research on the development of the Smart Shirt technology and deserve thanks. They would also like to thank Dr. Ken Mackenzie for his contributions to the development of the ‘in-fabric” network in the Wearable Motherboard. Finally, they would like to thank Dr. Bob Graybill of DARPA for providing funding under Contract # F30602-00-2-0564 for the recent research exploring the paradigm of “fabric is the computer.” References [1]
[2] [3] [4] [5] [6] [7] [8]
Gopalsamy, C., Park, S., Rajamanickam, R., and Jayaraman, S., “The Wearable Motherboard: The First Generation of Adaptive and Responsive Textile Structures (ARTS) For Medical Applications”, Journal of Virtual Reality, 1999; 4:152-168. SOFTswitch, http://www.softswitch.co.uk, Last Accessed: January 2004. “Musical Jacket Project “ www.media.mit.edu, Last Accessed: January 2004. Post, E. R., Orth, M., Russo, P. R., and Gershenfeld, N. IBM Systems Journal, 39 (3 &4), 2001. “Infineon’s MP3 Player,” http://www.siliconstrategies.com/story/OEG20020426S0101, Last Accessed: January 2004. DARPA BAA on Electronic Textiles, http://www.darpa.mil/baa/BAA01-41.htm, Last Accessed: April 11, 2003. Park, S., and Jayaraman, S., “Smart Textiles: Wearable Electronic Systems,” MRS Bulletin, August 2003, pp.586-591. Mann, S., “On the Bandwagon or Beyond Wearable Computing?” Personal Technologies, 1997; 1:203-207.
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[9] [10] [11] [12]
[13] [14] [15] [16]
[17]
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Mann, S., “Smart Clothing: The Wearable Computer and WearCam,” Personal Technologies, 1997, 1:21-27. Rajamanickam, R., Park, S., and Jayaraman, S., “A Structured Methodology for the Design and Development of Textile Structures in a Concurrent Engineering Environment,” Journal of the Textile Institute, 1998; 89, 3: 44-62. The Georgia Tech Wearable Motherboard™: The Intelligent Garment for the 21st Century, http://www.smartshirt.gatech.edu, Last Accessed: August 4, 2003. Park, S., Gopalsamy, C., Rajamanickam, R., and Jayaraman, S., The Wearable Motherboard™: An Information Infrastructure or Sensate Liner for Medical Applications, Studies in Health Technology and Informatics, IOS Press, 1999; 62: 252-258. Park, S., and Jayaraman, S., Enhancing the Quality of Life through Technology: The Role of Personalized Wearable Intelligent Information Infrastructure,” IEEE Engineering in Medicine and Biology, May/June 2003, pp.41-48. Park, S., and Jayaraman, S., “Adaptive and Responsive Textile Structures,” in Smart Fibers, Fabrics and Clothing: Fundamentals and Applications (ed. X. Tao), pp. 226245, Woodhead Publishing Limited, Cambridge, UK, 2001. Park, S., and Jayaraman, S., “Quality of Life in the Internet Age: Role of the Georgia Tech Smart Shirt”, Atlanta Medicine, Vol. 74, No. 4, pp. 24-28, Winter 2001. Mackenzie, K., Hudson, D., Maule, S., Park, S., and Jayaraman, S., “A Prototype Network Embedded in Textile Fabric,” in Proceedings of CASES 2001, International Conference on Compilers, Architecture and Synthesis for Embedded Systems, pp. 188-194, Atlanta, Georgia, November 16-17, 2001. Park, S., Mackenzie, K., and Jayaraman, S., “The Wearable Motherboard: A Framework for Personalized Mobile Information Processing (PMIP),” Special Session: E-Textiles, in Proc. ACM/IEEE 39th Design Automation Conference, New Orleans, June 10-14, 2002.
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Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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New Textile Materials for Environmental Protection Izabella KRUCIēSKA1, Eulalia KLATA, Michaá CHRZANOWSKI Department of Fibre Physics and Textile Metrology, Technical University of Lodz, Poland
Abstract. The properties of new filtering materials for protection of respiratory tracts composed of melt- blown PP nonwovens and electrospun layers of PAN fibres are presented. The materials manufactured are characterised by the following parameters: diameter of the electrospun fibres, filtering efficiency of sodium chloride aerosol and paraffin oil mist, breathing resistance and bacterial penetration. The analysis of the influence of the electrospinning process’ technological conditions on the value of the characteristics discussed is presented. Keywords: Filtering materials, electrospinning, protection of respiratory tracts
Introduction From prehistoric times till now, air pollution from hazardous chemical and biological particles is an essential threat to humans’ health. Together with the development of civilisation and escalation of the conflicts between nations, the risk of loss of health and even life due to polluted air increases considerably. Therefore the continuos development of the new materials used for protection of human respiratory tracts against hazardous particles is observed. The fibrous materials play a special role in this subject. Davies in his work ‘Air Filtration’ [1] has presented an interesting review of the earliest literature considering problems connected with filtering polluted air. For centuries, miners have used special clothes to protect nose and mouth against dust. Bernardino amazzini, who lived on the turn of the 17th century, in his work ‘De morbis artificum’ indicated the need for protection of the respiratory tracts against dusts of workers labouring in various professions listed by him. Brise Fradin developed in 1814 the first device, which provided durable protection of the respiratory tracts. It was composed of a container filled with cotton fibres which was connected by a duct with the user’s mouth. The first filtration respiratory mask was designed at the beginning of the 19th century with the aim of protecting the users against diseases transmitted by the breathing system. In these times, firemen began to use masks specially designed for them. The first construction of such a ‘mask’ was primitive: a leather helmet was connected with a hose which supplied air from the ground level. The construction was based on the observation that during fire, fewer amounts of toxic substances were at the ground level than at the level of the fireman’s mouth. In 1
Corresponding Author:
[email protected]
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addition, a layer of fibres protected the lower air inlet. John Tyndall, in 1868 designed a mask which consisted of some layers of differentiated structure. A clay layer separated the first two layers of dry cotton fibres. Between the two next cotton fibre layers was inserted charcoal, and the last two cotton fibre layers were separated by a layer of wool fibres saturated with glycerine. The history of the development of filtration materials over the 19th century has been described in a work elaborated by Feldhaus [2]. The 20th century left a lasting impression of the First World War, during which toxic gases were used for the first time. This was the reason that after 1914, the further history of the development of filtration materials was connected with absorbers of toxic substances manufactured with the use of charcoal and fibrous materials. The next discovery, which changed the approach to the designing of filtration materials, was done in 1930. Hansen, in his filter applied a mixture of fibres and resin as filtration materials. This caused an electrostatic field being created inside the material. The action of electrostatic forces on dust particles significantly increases the filtration efficiency of the materials manufactured. The brief historical sketch presented above indicates that textile fibres were one of the material components, which protect the respiratory tracts, and have been applied from the dawn of history. From the beginning they had been used intuitively, without understanding the mechanism of filtration. The first attempts of scientific description of the filtration mechanism were presented by Albrecht [3], Kaufman [4], Langmuir [5], and recently by Brown [6] who characterised the four basic physical phenomena of mechanical deposition in the following way : x direct interception occurs when a particle follows a streamline and is captured as a result of coming into contact with the fibre; x inertial impaction is realised when the deposition is effected by the deviation of a particle from the streamline caused by its own inertia;in diffusive deposition the combined action of airflow and Brownian motion brings a particle into contact with the fibre; gravitational settling resulting from gravitation forces. Illustration of the above mechanisms of filtration is presented in Figure 1.
Figure1.
Particle capture mechanism: A - particle captured by interception; B – particle captured by inertial impaction; C - particle captured by diffusive deposition [7].
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The analysis of equations determining the filter efficiency governed by the mechanisms specified above indicates that the most important parameters deciding about filtering efficiency are the thickness of filters, the diameter of fibres and the porosity of the filter. Identification of these phenomena was the basis for development of new technologies for filtering materials composed from ultra thin fibres. These technologies mainly are based on manufacturing the nonwovens directly from the dissolved or melted polymers using melt-blown technique, flashspinning and electrospinning. Additionally theoretical consideration also indicates that the activity of fibres on particles significantly increases if an electrostatic field is formed inside the nonwoven. This is the reason that nonwovens are additional modified. Three following groups of fibrous electrostatic materials used can be distinguished, based upon their ability to generate an electrostatic charge: x materials in which the charge is generated by corona discharge after fibre or web formation, x materials in which the charge is generated by induction during spinning in an electrostatic field, and x materials in which the charge is induced as the result of the triboelectric effect.
1. Review of techniques for manufacturing fibrous filtering materials The first nonwovens using melted organic polymers were manufactured in the 1950s, using a method similar to air-blowing of the polymer melt. Application of this latter method enabled super-thin fibres to be obtained with a diameter smaller than 5 Pm. The melt-blown technique of manufacturing nonwovens from super-fine fibres was developed by Wente at the Naval Research Laboratory in USA, [8]. Buntin, a worker at Exxon Research and Engineering introduced the melt-blown technique for processing PP into the industry [9]. Recently, the Nonwoven Technologies Inc., USA [10] has announced the possibility of manufacturing melt-blown PP nonwovens composed from nano-size fibres of a diameter equal to 300nm. To enhance the filtration efficiency, the melt -blown nonwovens are subjected to the process of activation, mainly using the corona discharge method. An overview of flash-spinning technologies is presented by Wehman [11]. Flashspun nonwovens made from fibres with very low linear density, which can be obtained using splittable fibres as a raw material for production of conventional webs. Subsequently, webs can be subjected to the classical needle punching or spunlace process during which sacrificial polymer is removed and fibres of low linear density are obtained. The flash-spinning process can be also accomplished using such bicomponent melt-blown technology which is based on spinning two incompatible polymers together and forming a web which is then subjected to the splitting process. Induction of electric charges is another mechanism used in filtering material technology. Induction consists of electric charge generation in a conductor placed in an electric field. Therefore, fine-fibres made from conductive solutions or melts, charged during electrostatic extrusion, belong to this group. Formation of nanofibres by the electrospinning method results from the reaction of a polymer solution drop subjected to an external electric field. This method enables manufacturing fibres with transversal dimensions of nanometers. Gilbert in 1600 made the first observation concerning the
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behaviour of an electroconductive fluid under the action of an electrical field. He pointed out that a spherical drop of water on a dry surface is drowning up, taking the shape of a cone when a piece of rubbed amber is held above it. One of the first investigations into the phenomena of interaction of an electric field with a fluid drop was carried out by Zeleny [12]. He used the apparatus presented in Figure 2 in his experiment.
Figure 2. Scheme showing the idea of an one-plate apparatus for electrospinning designed by Zeleny, [13].
The apparatus include an open-end capillary tube of metal or glass. The conductive fluid is delivered to this tube using the reservoir C. A plate B is mounted opposite to the capillary tube in a distance of h. The capillary tube and the plate are maintained at a given potential difference V using a high voltage generator. Formhals [14] used this kind of technology for spinning thin polymer filaments. The electric charges, which diffuse in the liquid, forced by the electric field, cause a strong deformation of the liquid surface in order to minimise the system’s total energy. The electric forces exceed the forces of surface tension in the regions of the maximum field strength and charge density, and the liquid forms a cone at the nozzle outlet. A thin stream of liquid particles is torn off from the end of the cone. Taylor [15] proved that for a given type of fluid, a critical value of the applied voltage exists, at which the drop of fluid, flowing from the capillary tube, is transformed into a cone under the influence of the electric field, and loss its stability. The critical value of this potential depends on the surface tension T of the fluid and of the initial radius of drop ro, taking the value of 1.62 (T/ro)1/2. Zeleny’s and Taylor’s investigations have been an inspiration for many researchers who carried out observations of the behaviour of different kinds of polymers in the electric field. These observations were the basis for the development of manufacturing technologies for a new generation of fibres with very small transversal dimensions. Schmidt [16] demonstrated the possibility of application of electrospun polycarbonate fibres to enhance the dust filtration efficiency. In the 1980’s, the Carl Freudenberg company used the electrospinning technology first commercially. Trouilhet [17] and Weghmann [18] presented a wide range of applications of electrospun webs especially in the filtration area. In that time the electrospinning method for manufacturing filtering materials did not find common application. The revival of this technology has been observed for the last five-four years. In 2000 Donaldson Inc., USA realised dust filters with a thin layer of nanofibres.
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A basic set for electrospinning consists form three major components, such as: a high voltage generator, a metal or glass capillary tube, and a collecting plate electrode, similar to the set designed by Zeleny. Such type of set is characterised by low productivity, usually less than 1 mLh-1. To solve this problem, the array of multiply capillary tubes should be developed. Experiments carried out indicate that due to the interference between the electrical fields developed around such system an uniform electrical field strength cannot be ensured at the tip of each tube. For such a system, high probability of the tube clogging appears. To avoid such problems during the electrospinning process, some authors proposed to spin the fibres directly form the polymer solution surface. A new method with high productivity was developed by Jirsak at the Technical University of Liberec [19]. The proposed invention was commercialised by Elmarco company. The idea is very simple. The set is composed from two electrodes. The bottom electrode formed in the shape of a roll is immersed in the solution of a polymer, as shown in Figure 3.
Figure 3. The idea of the electrospinning method developed by Jirsak.
A thin layer of polymer solution covers the rotating electrode, and multiple jets are formed due to the action of the electrical field. The Elmarco company offers a wide assortment of spun-bonded nonwovens covered by nanofibre membrans made of polyamide, polyurethane and polyvinyl alcohol. A further approach related to spinning directly from the solution surface was invented by Yarin and Zussman [20]. The proposed system is composed from two layers: a bottom layer in the form of ferromagnetic suspension and an upper layer in the form of polymer solution. The two- layer system is subjected to the magnetic field provided by a permanent magnet. The scheme of this apparatus is presented in Figure 4.
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Figure 4.. The idea of manufacturing electrospun nonwovens directly from the surface of a polymer solution: a- ferromagnetic suspension, b- polymer solution, c-upper electrode, d- lower electrode, e- high voltage generator, f- permanent magnet [20].
Vertical spikes of magnetic suspension appear as the result of action of the magnetic field, what causes the perturbation of the free surface of the polymer solution (see Figure 5). Under the action of the electrical field, perturbations of the free surface become the sites of jetting directed upward.
Figure 5. An image of the protruded parts of a polymer layer located above the magnetic fluid [20].
Research into electrospun materials has been carried out in Poland over the last three years. Attention is paid mainly for medical [21] and filtering materials [22]. The aim of this paper is to discuss the possibility of manufacturing filtering materials used for protection of respiratory tracts, and classified in accordance with the European Standard EN 143 as P3, characterised additionally by the ability to prevent the penetration by micro-organisms. In order to enhance the generation of charge inside the product, the filtering material is designed as a two- layer sandwich. One layer is made
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from PP melt blown nonwoven and the second layer is composed from PAN electrospun fibres (e- fibres).
2. Experiment 2.1 Preparing of the PAN solutions Electrospinning was conducted from 13, 15 and 17 wt % spinning solutions of polyacrylonitrile (PAN) produced by Zoltek Rt, Hungary in dimethyl sulfoxide (DMSO). The intrinsic viscosity of PAN was equal to 1.3r0.02 dL/g. The surface tension of polymer solutions was determined using SIGMA 701, KSV tensiometer. The results of investigation of the value of surface tension are given in Table 1. Table 1. Surface tension of the investigated solution PAN/DMSO solutions Composition of samples 13% PAN
Surface tension [mN/m] 42.788
Standard deviation [mN/m] 0.078
15% PAN
43.422
0.021
17% PAN
43.734
0.207
2.2 Manufacturing nanofibres from PAN solution The web composed of PAN nanofibres was formed with the use of a laboratory prototype stand special designed for nonwonen manufacturing by the electrospinning technique. Two electrodes are the basic system elements, from which one, connected with a syringe for extruding the polymer, enables the polymer drops achieve a suitable electric potential. The next important element of this system is the second electrode, the take-up electrode, in relation to which the electric potential of the polymer is applied, and on which the fibres are deposed during the nonwoven manufacturing process. This electrode can be of different shapes; we proposed the shape of a flat plate. The both electrodes are mutually insulated. The whole system is insulated from external electric fields by a screen, which serves as a Faraday-cage and additional isolates against air whirls. The fibres were spun on the substrate in a form of PP melt-blown nonwovens of surface mass equal to 32.1g/m2. In the first stage of research, our interest was concentrated on investigation of the influence on fibre formability of technological parameters, such as: the polymer concentration in solvent, the voltage applied and the distance between the end of the capillary tube and the collecting electrode. The values applied of all three parameters are specified in the Table 2.
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Table 2. Specification of the technological parameters applied during the electrospinning process Type of technological parameter PAN concentration in solution Voltage Distance between capillary tube and collecting electrode
Values of technological parameter 13%,15%,17% 10kV, 15kV 10,20,25 cm
2.3. Methodology of characterisation of PAN nano-fibre filtering material To characterise the nano-fibre filtering materials, the following investigations were realised: x the diameter of the fibres obtained was determined using SEM method, x the filtering efficiency was determined according EN 143 method using sodium chloride aerosol and oil mist method, x the breathing resistance was determined according to EN143 method, x the bacterial penetration was determined according to an originally developed methodology by Majchrzycka and Gutarowska [23]. The penetration of aerosol particles through the filtration material is measured by the ratio of the aerosol particle concentration after and before passing the filter. Sodium chloride is used which represents an aerosol with dispersed solid phase. The test with oil mist is a tool for estimation of filtration efficiency against aerosols with dispersed fluid phase. A form of the dispersed medium with known particle sizes has been chosen to estimate the test -aerosol penetration. An aerosol of sodium chloride particles is generated by atomising a 1 % aqueous solution of NaCl salt and evaporating water. The aerosol produced by this method is polydisperse with a mass mean particle diameter of approximately 0.6 Pm. An aerosol of paraffin oil droplets is generated by atomising heated paraffin, oil which results in a median Stokes’ particle diameter value equal to 0.4 Pm. By ‘breathing resistance’ we mean the resistance which the respiratory protective equipment, or its elements, causes to the airflow through them. The breathing resistance is a parameter that determines the usability features of the respiratory tract protecting equipment. It represents the user’s ability to perform correct physiological breathing functions while using filters or filtration half-masks. The measuring principle is based on passing air at room temperature, at atmospheric pressure, and at a humidity which does not cause condensation, through the object tested. The air is passed through the filter at a rate of 30 and 95 l/min, and the pressure drop after the filter is measured in relation to the atmospheric pressure. The acceptable airflows to meet the tests correspond with minute lung ventilation during light and hard work, and are related to the inspiration phase. The bacterial penetration was determined using the method developed by Majchrzycka and Gutarowska [23]. The method is based on the analysis of penetration of microbiological aerosol flowing through the tested specimen and through the reference microbiological filter characterised by the filtering efficiency equal to 99.999%. The reference filter is placed behind the tested samples. The developed test allows to determine the amount of micro-organisms trapped by the filtering sample tested and by the reference microbiological filter. At the beginning of measurements,
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the amount of micro-organisms carrying by aerosol is evaluated by completing the test without the evaluated filtering materials. Based on the results obtained it is possible to calculate the filtering efficiency of micro-organisms by the materials tested. The filter performance was determined against the two types of micro-organisms: Escherichia coli type ATCC10536 and Staphylococcus aureus type ATCC6538. 2.4. Results and discussion The realisation of the experiment designed led to manufacturing the filtering materials presented in Figure 6.
Figure 6. View of the two-layer filtering material melt-blown / electrospun.
The samples were subjected to a series of laboratory tests according to the methodology described above. The results of investigations related to e-fibres and filtering materials designed are given in Table 3.
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Table 3. Characteristics of developed filtering material with a layer of e-spun fibres
Voltage 10 kV Polymer Concentration
13 %
15 %
17 %
13 %
15 %
17 %
Distance between electrodes
Diameter of fibres nm
10 cm 20 cm 25 cm 10 cm 20 cm 25 cm 10 cm 20 cm 25 cm
390 386 360 440 470 470 660 680 630
10 cm 20 cm 25 cm 10 cm 20 cm 25 cm 10 cm 20 cm 25 cm
400 350 310 420 400 380 480 510 570
Oil mist (%) NaCl (%) penetration penetration 60 l/min, 60 l/min, 12.2 cm/s 12.2 cm/s 3.87 1.86 3.11 1.06 2.11 0.99 1.62 0.36 4.35 2.47 3.96 2.59 7.58 5.88 6.52 4.12 2.78 2.28 Voltage 15 kV 6.35 6.09 1.37 0.28 3.65 1.57 3.05 1.41 0.51 0.09 4.32 2.81 5.05 4.96 2.82 1.24 1.78 0.96
Resistance (Pa) 48 l/min 9.8 cm/s 425.8 251.6 186.6 543.6 189.1 146.7 180.6 164.5 156.0
Layer of nanofibres g/m2
130.8 294.3 169.3 211.1 338.8 113.9 107.6 277.2 221.0
4 3.2 2.8 5.2 3,8 2,5 4.5 7.6 7.2
6.2 3.7 2.8 5.1 5.2 3.6 6.5 5.1 4.6
The results presented in Table 3 indicate that the fibre diameter changes as a function of the polymer concentration, the distance of collecting electrode from nozzle, and the value of applied voltage. Analysing the values of fibre diameter, generally we can conclude that the application of higher polymer concentration, lower distance between collecting electrode and nozzle, and lower value of voltage results in obtaining higher values of the e-fibre diameters. The fibres formed using a 17% polymer concentration in the solution are the exception form this rule. For this kind of concentration, the diameter of fibres increases with the increase in the collecting distance. The application of a 10 cm distance between the collecting electrode and the nozzle results in manufacturing many fibres adhering one to another. Therefore this value of the distance should be eliminated in further investigations. The results obtained of the area mass of the layer of nano-sized fibres indicate that the applied process is still not stable. We obtained different values of area mass of the e- spun layer, despite the fact that for each variant we used the same amount of polymer solution. Therefore it is very difficult to determine a correlation between the technological process’ parameters, the diameter of e- spun fibres, and the filtering properties of the developed material. Despite this fact, the main achievements of the experiment carried out, is the manufacturing such a variant of filtering materials whose properties are very close to those required for filtering material of class P3. This variant was manufactured under the following conditions: concentration of polymer solution was equal to 15%, the value of voltage applied was 15kV and the collecting distance was 20 mm. The filtration efficiency of NaCl aerosol for this variant was equal to 99.49%, the filtration efficiency of oil mist after one minute was equal to 99.91%, and
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the breathing resistance took the value of 338.8 Pa. The effect of enhancement of filtering efficiency of the material developed can be illustrated by comparing the characteristics of melt-blown nonwovens uncovered and covered with e-spun fibres. These characteristics are given in Table 4.
Table 4 Characteristics of covered and uncovered layers of melt- blown nonwovens with e- spun fibres Type of material
NaCl (%) penetration 60l/min, 12.2 cm/s 16.62
Melt- blown nonwovens
Melt- blown 0.51 nonwovens covered with e-spun fibres
Oil mist (%) penetration, 60 l/min 12.2 cm/s,1 min 19.40
Oil mist (%) penetration, 60 l/min 12.2 cm/s, 3 min 25.31
Resistance (Pa) 48 l/min 9.8 cm/s
0.09
0.11
338.8
37.3
The results of the filtration efficiency of the bio-aerosols by the filtering materials designed are given in Table 5. The characteristics presenting in Table 5 indicate that covering the melt-blown nonwovens with e-spun fibres results in the increase of the filtering efficiency of the bio-aerosols to the value of 99.966% for Staphylococcus aureus and to the value of 99.895% for Escherichia coli. Table 5. Filtration efficiency of bio-aerosols of covered and uncovered layers of meltblown nonwovens with e- spun fibres Type of material Melt- blown nonwovens Melt- blown nonwovens covered with e-spun fibres
Filtration efficiency of Escherichia coli 99.846%
Filtration efficiency of Staphylococcus aureus
99.895%
99.996%
99.988%
3. Conclusions Thanks to the experiments carried out, the preliminary investigation into the new materials for protection of respiratory tracts was completed. The material developed is composed of one layer of PP melt-blown nonwoven and one layer of electrospun PAN fibres. The main achievement of the experiment is the selection of a range of technological parameters which enables manufacturing filtering materials with high resistively for penetration of NaCl and paraffin oil aerosol. Especially promising results were obtained for the oil mist test completed during 3 minutes. This material was
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manufactured under the following conditions: concentration of polymer solution was equal to 15%, the value of applied voltage was 15kV and the collecting distance took the value of 20 mm. For this variant the filtration efficiency of NaCl aerosol was equal to 99.49%, the filtration efficiency of oil mist after one minute was equal to 99.91% and after three minutes took the value of 99.89%, and the breathing resistance took the value of 338.8 Pa. The analysis of the bio-aerosol penetration after application of the espun fibre layer showed out a decrease of the values of the parameters discussed for both micro-organisms i.e. Staphylococcus aureus o the value of 0.004% and Escherichia coli to the value of 0.105%. Acknowledgement We would like to thank the company Filter Service, Poland for kindly supporting our investigation. References [1] Davies C N (1973), Air Filtration Academic Press, London. [2] Feldhaus G M (1929), Schutzmasken in vergangenen Jahrhunderten, Die Gasmaske, 1, 104. [3] Albrecht F (1931), Theoretische Unterschungen über die Ablegerung von Staub und Luft und ihre Anwendung auf die Teorie der Staubfilter, Physik, Zeits, 32, 48. [4] Kauffman A (1936), Die Faserstoffe für Atemschutzfilter Z. Verein Deutsches Ing., 80, 593. [5] Langmuir I (1942), Report on Smokes and Filters, Section I, U. S. Office of Scientific Research and Development, no 865, Part IV. [6] Brown R C (1993), Air Filtration. An Integrated Approach to the Theory and Applications of Fibrous Filters, Pergamon Press. [7] GradoĔ L, Majchrzycka K (2001), Efektywna ochrona ukáadu oddechowego przed zagroĪeniami pyáowymi, CIOP, Warsaw, Poland. [8] Wente A (1956), Superfine thermoplastic fibres, Industrial Engineering Chemistry, 48, 13. [9] Buntin R R (1973), Melt-blowing a one step web process for new nonwoven products, Tappi, 56, 74. [10] NTI advances melt-blown nanofibre technology, Filtration and Separation, 2005. [11] Wehman M (2004), Innovative nonwovens in filtration, CD Proceedings of 7. Symposium ‘Textile Filter”, Chemnitz, Germany. [12] Zeleny J (1914), The electrical discharge from Liquid Points, and a Hydrostatic Method of measuring the electric intensity at their surface, Phys.Rev, 3, 69-91. [13] Taylor,G., Van Dyke, M., D., Electrically driven jets, Proc. Roy. Soc. London, vol.313, pp. 453-475, 1969. [14] Formhals A (1934) , Process and apparatus for preparing artificial threads. US Patent, No.1 975 504. [15] Taylor G I (1964), Disintegration of water drops in an electric field, Proc R Soc Lond A, 280, 383-397. [16] Schmidt K (1980), Manufacture and use polycarbonat felt pads made from extremely fine fibres, Melliand Textil., 61, 495-497. [17] Trouilhet Y. (1981), Advances in web formation, EDANA, Brussels.
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[18] Weghmann A (1982), Production of electrostatic spun synthetic microfibre nonwovens and applications in filtration, Proceedings of the 3 rd World Filtration Congress. [19] Jirsak,O., Cz Patent ,2003-2414 (2994274). [20] Yarin, A., Zussman, E., Upward needleless electrospinning of multiple nanofibers, Polymer, vol.45, 2977-2980, 2004. [21] BáasiĔska, A, KruciĔska, I., Chrzanowski, M, Dibutyrylchitin nonwoven biomaterilas manufactured using electrospinning method, Proceedings of World Textile Conference - 4th AUTEX Conference, Roubaix, France.. [22] Klata, E., Babeá, K., KruciĔska, I., Preliminary investigation on carbon nanofibres for electrochemical capacitors, Proceedings of World Textile Conference - 4th AUTEX Conference, Roubaix, France, 2004. 2004. [23] Majchrzycka, K, Gutarowska, B., private communicate.
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Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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Wearable Mechanosensing and Emerging Technologies in Fabric-based Actuation Danilo DE ROSSI1, Federico CARPI, Federico LORUSSI, E. Pasquale SCILINGO, Alessandro TOGNETTI Interdepartmental Research Centre “E. Piaggio”, University of Pisa, Italy Abstract. Kinesthetic and haptic interfaces between humans and machines are currently under development in a truly wearable form, using innovative technologies based on electroactive polymers. The integration of electroactive polymeric materials into wearable garments is a viable means to confer them strain sensing and actuation properties. The methodology underlying the design of kinesthetic and haptic systems with the combined use of new polymeric electroactive materials in configurations compatible with a textile substrate can provide new avenues toward the realization of truly wearable interfaces. In this chapter, the conception, early stage implementation and preliminary testing of fabric-based wearable interfaces endowed with spatially redundant strain sensing and simple actuation properties are illustrated with reference to preliminary prototypes. Keywords. Wearable, interface, fabric, mechanosensing, actuation, electroactive polymer.
Introduction Wearable kinesthetic and haptic interfaces between humans and machines are regarded today as systems capable of supporting a large number of activities in different healthfocused disciplines, such as biomonitoring, rehabilitation, telemedicine, teleassistance, ergonomics and sport medicine [1-9]. Such wearable interfaces are conceived as innovative fabric-based garments, integrating at least sensing and actuation devices [1-9]. Due to their multifunctional interactivity, enabled by wearable devices that are flexible and conformable to the human body, these kinds of interfaces may be considered as promoters of a higher quality of life and progress in several fields of application. In particular, disciplines dealing with a monitoring of body kinematics would considerably benefit from the implementation of wearable sensorised systems. In particular, garments with strain sensing capabilities would enable the tracking of posture and gesture of a subject and would permit analyses of 1 Corresponding author: Interdepartmental Research Centre “E. Piaggio”, University of Pisa, School of Engineering, via Diotisalvi, 2 – 56100 Pisa, Italy. E-mail:
[email protected].
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kinematic variables of interest [7]. Likewise, the integration into skin-adherent clothes of actuators represents a potentially useful tool for disciplines like rehabilitation [10]. Actuators may provide enduring mechanical support to lost motory functions (compensation of disabilities) or to their physiotherapeutic restoration. These actions could be performed either by following predefined tasks or by exploiting the strain and stress information produced by co-integrated sensors. The active support offered by wearable actuators could also favour the improvement of sports training techniques or the prevention of risks related to abnormal stress distributions and overloading. The long-term goal of our research is to develop a family of truly wearable and bidirectional (i.e. embedding sensing and actuating functions) interfaces. In order to achieve this distant goal, several methodologies and techniques still need to be developed, in terms of sensing (tactile and kinesthetic) and actuation. Promising recent developments in material processing, device design and system configuration push the concentration of efforts towards the realization of such wearable interfaces. In fact, sensors and actuators can be made of polymeric materials, in order to be suitably embedded into fabric substrates. In particular, the intrinsic sensing and actuating properties, elasticity, lightness, flexibility and relatively low cost of many electroactive polymers make them suitable materials for the realization of useful devices [9]. Although the realization of such fabric-based wearable interfaces is one of our main objectives, it can appear somewhat futuristic. Nevertheless, we have focused our efforts on this application and progressed towards preliminary prototypes. The aim of this chapter is to give a picture of the already-demonstrated or potential use of electroactive polymers for fabric-based strain-sensing and actuating devices.
1. Wearable Mechanosensing Biological kinesthesia is internally based on planning mechanical events by relying largely on the activity of the subject and on an inherent bidirectional flow between peripheral receptors and Central Nervous System (CNS). Artificial human-like kinesthetic systems should be able to adequately embed artificial signals referable to the joints possibly in a structured map of local inputs from a number of individual joints. Presently, however, human movement tracking systems generate only sparse real-time data [11]. Improvements in accuracy, spatial resolution and parallel processing will lead to devices suitable for tracking fine manipulations and complex gestural recognition. Trajectory tracking of joint should not depend on sensor technology and location. In available sensing gloves usually sensors in a finger are located to detect a planar movement for each degree of freedom; in several cases a single sensor on the back of each joint should unambiguously signal joint position and movement. However, joint surface geometry dictates some degree of associated rotation, unless an intended and undetected counterrotation cancels it. On the other hand, from a functional point of view, such rotation is not influential in the sense that it is a part of the only permitted movement. In this case, the sensor displays a one to one correspondence between the trajectories parameterized in a certain curvilinear frame (which includes rotations) to a set of values, which exactly reconstructs the position. A
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major problem is the embedding of this manifold into Cartesian space (i.e. the definition of the geometry, including rotation in the Cartesian frame). What we propose in section VI is in an identification procedure that permits the control system to test a redundant sensor set and reconstructs a global input-output function. This step could correspond to a learning phase in which the CNS also acquires knowledge on the muscular-skeletal system it has to control. 1.1. Wearable sensing system In biological systems the intrinsic noisy, sloppy and poorly selective properties of individual mechanoreceptors are largely compensated by redundant allocation, powerful peripheral processing and efficient and continuous calibration through supervised and unsupervised learning and training. A truly biomimetic sensing system should replicate these features to some extent not just as a mimicking exercise, but as a result of solid engineering reasoning. Guided by these arguments we investigated on strain sensing elastic fibers and fabrics to realize adherent wearable systems with excellent mechanical matching with body skin. Sensing fabrics are obtained by spreading a conductive solution, based on Conductive Elastomer (CE) composites, over cotton-Lycra threads. CE composites show piezoresistive properties when a deformation is applied and can be integrated into fabric or other flexible substrate to be employed as strain sensors. Integrated CE sensors obtained in this way may be used in posture and movement analysis by realizing wearable kinesthetic interfaces [6]. The CE we used is a commercial product by WACKER Ltd (Elastosil LR 3162 A/B) [12] and it consists of a mixture containing graphite and silicon rubber. WACKER Ltd guarantees the non-toxicity of the product that, after the vulcanization, can be employed in medical and pharmaceutical applications. According to the articular body segment to monitor, a suitable adhesive mask is realized and placed on the corresponding area on the fabric shirt, or however over a piece of fabric which afterwards will be used to sew the sensing garment. Smearing the conductive mixture over the mask it will fill the empty areas and after removing the mask the desired topology of sensors is left on the fabric. The mask is cut by a laser milling machine. After the CE deposition, the mask is removed and the treated fabric is placed in an oven at a temperature of 130°C to speed up the cross-linking process of the mixture. In about 10 minutes the sensing fabric is ready to be employed. 1.2. Sensing features A detailed characterization of CE sensors consisting in finding the relationship between the electrical resistance R(t) of a treated fabric sample and its actual length l(t) has been done, both in static and dynamic configuration. Moreover, an analysis of the thermal transduction properties and aging of the fabric has been performed. In terms of quasi-static characterization, a sample 5 mm wide shows an unstretched electrical resistance of about 1 kҏ per cm, and its gauge factor GF about 2.8 (GF=l(R-R0)/R(l-l0)), where R is the electrical resistance, l is the actual length, R0 is the electrical resistance corresponding to l0, which represents the rest length of the specimen. The temperature coefficient ratio is 0.08 K-1. Capacity effects showed by the sample are negligible up to 100 MHz.
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The dynamic characterization led us to address two main issues. The first one concerns the duration of the transient time, which can take up to several minutes. Human movements, hence, cannot be described using these sensors without a suitable signal processing aimed at compensating the intrinsically slowness. The latter issue refers to non-linearity of the electrical behavior of the analyzed specimens under certain working conditions, i.e. when fast strains are applied. Both shortcomings have been addressed and solved by means of a dedicated algorithmic strategy and a redundancy strategy. 1.3. Identification and inversion algorithm A redundant distribution of sensors can also cope with the complex identification of the movement trajectories of body segments to monitor. A suitable strategy has been arranged. It implies two phases: posture recording mode and identification. Preliminarily, some of the basic positions during the posture recorder mode are gathered by means of traditional devices (Figure 1) and used to construct a continuous function, which maps positions into sensor values. This map, obtained as an interpolation of the discrete function, which recognizes recorded posture, can be used to detect any position of the body segment (hand, arm, leg, etc.) (Figure 2), even though it has never been hold.
Figure 1. Recording phase of a predefined set of posture by means of conventional sensors.
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Figure2. Sensing fabric garments to monitor specific body segments.
Indeed, the identification algorithm is able to construct a model of the limb expressed in terms of sensor values. If the basic recorded positions are associated to a set of angle deviations for the joints of the limb, by means of a set of electrogoniometers, the inversion algorithm is able to reconstruct positions (in terms of angles) never assumed by the subject. Firstly, let us make some considerations on what does determination of human posture mean by using these wearable sensors and how sensor networks can be employed. To define formally a posture, it is necessary to develop a physical model for the particular subject holding it. We attribute a certain number of cartesian frames, one for each considered degree of freedom. In this sense, a posture is simply the set of the mutual positions with respect to the fixed frames. Obviously, not the entire set of the mutual positions is necessary to reconstruct a posture exactly, and a minimal set can be chosen in many different ways. The Denavit-Hartemberg formalism [13], for example, fixes exactly the number of relationships between frames and gives a standard method to write these positions in terms of rotation and translation affinities, for rotational and translational joints. In case that the topological structure of the kinematic chain under study cannot be linearly approximated, it is still possible to define a model by using more sophisticated non-linear approaches, [14], to describe the kinematics more accurately. For example, for the kinesiology of the hand, we refer to [15] and [16], while the model for the finger kinematic chains is substantially reported in [17]. The problem can be formalized as follows. Let us assume a fixed state space (described by a set of frames assigned and by their mutual coordinate transformations) which we will designate as the posture space and which admits a well defined topological model. To survey posture it is necessary to construct a metric on this space and then to relate the elements of the posture space to the electrical sensor configurations that span the space of sensor readings. It is assumed that they are able to detect a variation in subject posture and that there exists an invertible function that maps the space of the postures into the space of the sensor readings. As a consequence, the image of the posture space through the invertible function is a subset of sensor recordings space, which has the same dimension of posture space itself. Therefore, the inverse of this function can be used to infer the posture from the electrical readings. The construction of this function, or ”system identification”, is the crucial point of the method, and it is important from several points of view. It is worth
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pointing out that this phase is not a single sensor calibration, but a real identification of the entire system. In fact, for several reasons (the most important being the variability of body structure of the subject), the sensor location is not precisely known. However, adopting the described approach, this is no longer essential, neither is the map relating the size of a particular sensor to its electrical resistance. To better explain this point, one should consider that adherence of a sensorized fabric to the subject gives rise to intrinsic cross talk phenomena, due to the nature of the textile on which sensor are positioned. This fact, instead of being an inconvenience, is instrumental to the method we have developed, and ensures the possibility of reconstructing posture without the knowledge of the location of every single sensor. The identification concerns not only the set of sensors, but also the body structure of the subject. The same garment can be then used, in principle, to detect the posture of many different subjects with the prescribed accuracy, shifting all the variability on a different function. Metric introduction in the space of postures is realized simultaneously with the construction of the identification function. The basic idea is to relate information originating from a conventional measurement system (set of electrogoniometers, in this case) to the electrical state of a set of sensors. The former is obtained for a set of postures suitably chosen according to the topological structure of the posture space. This care is necessary because the posture space, related to anatomical variables such as bones and joint positions, is not directly accessible to the observer. Through multivariate interpolation techniques of the function mapping sensor measurements into postures, the subject postures have been successfully identified. Several experimental tests have been performed where actual postures measured by electrogoniometers have been compared with the output of the interpolating function and results have been encouraging and promising for future developments.
2. Emerging Technologies in Fabric-based Actuation In order to endow fabrics with macroscopic actuating functions, the sole technology currently available today is offered by fibres made of shape memory alloys (SMAs). Nitinol is the most common representative of this kind of materials. SMAs show the shape-memory effect: after having been deformed in a permanent state at low temperature, they are able to recover their original shape if heated up to a characteristic transition temperature. In particular, the material shows two stable phases: a low temperature phase called martensite and a high temperature phase called austenite. While the SMA is in the martensite phase, it can be deformed; however, it can recover its primary form by the reverse transformation upon heating. According to this shape-memory effect, these adaptive materials are able to convert thermal energy into mechanical work. Temperature variations can be induced either by direct heating or by Joule effect (by imposing an electrical current along the fibre). The second case is more practical and enables an electrical driving of the actuators. SMA fibres have been demonstrated to be able to provide actuating functions to textile substrates. As an example of application, they have been inserted into curtains, so that to make them able to respond to temperature variations by modifying the woven structure of
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the textile. In particular, the temperature increase up to the typical activation threshold (induced either by an applied electric current or by environmental conditions) can activate the fibres and ‘invigorate’ the textile. Accordingly, the textile structure can be switched between ‘open’ and ‘closed’ states, suitable for controlled heat and air diffusions or light propagations [18,19]. A different type of application has been proposed by D’Appolonia, by integrating into fabrics some Nitinol fibres with thermal memory effect [20]. This company has developed a shirt with woven SMA yarns, providing shape recovery capabilities. The sleeves of the shirt are capable to roll up when the environmental temperature becomes too warm, as presented in Figure 3. Despite these few examples, no successes towards an effective and comfortable embedding of actuating functions into textiles have been substantially reported so far. In this respect, it is opportune to underline that SMA fibres are basically metallic wires, which inevitably stiffen the textile substrate, decreasing the comfort of the wearable system. Furthermore, the shape-memory effect relies on heat diffusion across the material: this determines response speeds limited by the time constant of the diffusion process. Finally, the presence of hysteresis can be responsible of a tendency to thermal saturation, which negatively affects the actuation performance. For these reasons, different solutions for the embedding of efficient actuating functions into fabrics are demanded. Electroactive polymer (EAP) based actuators may be employed for such a purpose. In recent years, the development of EAP actuators in suitable fibre forms has been investigated in our laboratory as a first challenging solution to this problem. The fabrication of actuating devices with polymers in fibre geometry implies the need of overcoming several difficulties, such as the identification of efficient principles of operation and suitable configurations, selection of high-performance materials and implementation of custom fabrication processes. In this context, fibre-like EAP actuators made of conducting polymers and carbon nanotubes have been fabricated and tested. Conducting polymer (polyaniline) fibres [21] have been shown to exhibit sizeable active strains of the order of 1%, active stresses up to tens of MPa, driving electrical potential differences of few Volts and built-in tunable compliance. However, despite recent improvements [22,23], at present the use of such actuators is limited by the high value of their response time constants and their short lifetimes, both factors being determined by the need for an electrochemical driving force. Likewise, carbon nanotube fibres have been fabricated and preliminarily characterised as actuators.
Figure 3. D’Appolonia shirt with thermal memory effect (adapted from [20]).
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The projected superior mechanical and electrical properties of carbon nanotubes (high actuating stresses, low driving voltages and high energy densities) suggest that high actuating performances may be expected [24]. However, despite the very recent development of high-quality fibres and yarns [25], the actuation technology based on carbon nanotube fibres has still to be greatly improved, to be practically useful for macroscopic applications. As a remark, it is here underlined that, regardless the type of material employed for the development of actuating fibres, mechanisms for mechanical amplification of their strain can be taken into consideration. As an example, a bundle of fibres may be arranged in a configuration inspired to the McKibben pneumatic muscle [26]. In particular, a bundle of active fibres may be covered by a braid mesh (with flexible but not extensible threads), clamped at one end. Following an electrically-activated radial strain of the bundle, the system may be able, in principle, to change dimensions, by increasing its diameter and decreasing its length. This corresponds to a variation of the angle D between the axis of the system and the threads. It has been theoretically shown that, if the initial value of D is larger than S/4, the radial expansion is transduced into a linear contraction with an amplification factor larger than 1 [27]. Despite these studies, the fibre-oriented approach has to be currently considered as a long-term possible solution for the development of efficient fabric-based actuators. A large number of very challenging issues need to be addressed for such a purpose and it is hard to predict today whether this approach will be one day actually successful or not. Accordingly, we are currently performing parallel evaluations of different approaches, which may lead to short-term interesting results. In this regard, we are investigating the feasibility of using dielectric elastomer actuators with suitable planar configurations. This type of materials, belonging to the EAP family, can be used for electromechanical actuation, according to a simple principle of operation. The elementary form of such a device consists of two parallel compliant electrodes separated by a dielectric elastomer, which is deformed by the application of a high electric field between the electrodes. The thickness of the elastomer decreases while its surfaces expands [28,29]. Silicone rubbers are being tested as dielectric elastomers capable of high-strain wearable actuators. Dielectric elastomers possess several advantages: actuation strains up to the order of 100%, fast response times (down to tens of milliseconds) and generated stresses up to the order of 1 MPa. The price for achieving such performances is represented by the very high driving electric fields needed (order of 100 V/μm) [29]. We are currently developing the integration into fabrics of planar dielectric elastomer actuators. The idea is to combine the compliance of the actuator itself with that of suitable elastic fabrics, in order to be able to modify their shape or dimensions. For this purpose, we are using Lycra/cotton textiles as substrates for the deposition of layers of dielectric elastomer, as shown in Figure 4.
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Figure 4. Schematic drawing of a textile fabric substrate with deposited dielectric elastomer planar actuators.
Several materials, deposition methods and actuating configurations are under evaluation, in order to identify the best performing combination for the application of interest. This approach may provide a viable means to confer elementary actuating functions to fabrics for simple and low-force actuation tasks. 3. Conclusions This chapter has highlighted some basic issues related to the development of ready-to-use truly wearable systems, to be employed as kinesthetic and haptic interfaces between humans and machines, integrating sensing and actuation devices. Electroactive polymer based devices to be embedded into elastic fabrics have been shown to represent the best candidates for such a purpose. The advanced state of development of fabric based strain sensors enables at present the fabrication of prototypes of sensorised garments, satisfying several relevant needs. This contributes to make realistic the scenario towards the short-term realization of highperformance wearable interfaces. Nevertheless, much more work has to be done before efficient, reliable and small-size actuators can be fabricated and integrated into fabrics, in order to embed actuating functions into interactive interfaces. References [1] [2]
[3]
D. De Rossi, A. Della Santa, A. Mazzoldi, Dressware: wearable hardware, Mat Sci Eng C 7 (1999), 31-35. D. De Rossi, F. Carpi, F. Lorussi, A. Mazzoldi, E. P. Scilingo, A. Tognetti, Electroactive fabrics for distributed, conformable and interactive systems, Proc. IEEE Sensors 2002, Hyatt Orlando, Florida, October, 2002. D. De Rossi, F. Lorussi, A. Mazzoldi, P. Orsini, E. P. Scilingo, Active dressware: wearable kinesthetic systems, in Sensors & Sensing in biology & Engineering, J. Secomb Ed. New York: Springer Verlag (2003), 381-394.
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D. De Rossi, F. Carpi, F. Lorussi, A. Mazzoldi, R. Paradiso, E. P. Scilingo, A. Tognetti, Electroactive fabrics and wearable biomonitoring devices, AUTEX Research J. 3 no. 4 (2003), 180-185. A. Tognetti, F. Carpi, F. Lorussi, A. Mazzoldi, P. Orsini, E.P. Scilingo, M. Tesconi and D. De Rossi, Wearable Sensory-Motor Orthoses for Tele-Rehabilitation, Proc. of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Cancun, Mexico, September, 2003. F. Lorussi, W. Rocchia, E. P. Scilingo, A. Tognetti and D. De Rossi, Wearable, Redundant Fabric-Based Sensor Arrays for Reconstruction of Body Segment Posture, IEEE Sensors J., 4 no. 6 (2004), 807-818. A. Tognetti, F. Lorussi, R. Bartalesi, S. Quaglini, M. Tesconi, G. Zupone and D. De Rossi, Wearable kinesthetic system for capturing and classifying upper limb gesture in post-stroke rehabilitation, J. NeuroEngineering and Rehabilitation (2005), 2:8. D. De Rossi, F. Carpi, F. Lorussi, R. Paradiso, E. P. Scilingo, A. Tognetti, Electroactive fabrics and wearable man-machine interfaces, in Wearable electronics and photonics, X.-M. Tao Ed. Cambridge: Woodhead Publishing Limited, 2005. F. Carpi and D. De Rossi, Electroactive polymer based devices for e-textiles in biomedicine, IEEE Trans. On Information Technology In Biomedicine, In press. P. F. Binkley, Predicting the potential of wearable technology, IEEE Eng Med Biol 22 no. 3 (2003), 23-27. Mulder A., Human movements tracking technology. Hand Centered Studies of Human Movement Project. Tech. Rep., Simon Fraser University, school of kinesiology (1994). http://www.wacker.com J. Denavit, R.S. Hartenberg, A Kinematic Notation for Lower-Pair Mechanism Based on Matrices, Journal of Applied Mechanics (1955), 215-221. D. J. Montana, The kinematics of contact and grasp. Int. J. of Robotics Research, 7 no. 3 (1988), 17-32. I. A.Kapandji, Physiologie articulaire. Sch´emas comment´es de m´echanique humaine. Tome 1: Membre Superieur, Ed. Maloine Paris (1999). M.A. McConnail ,J.V. Basmajian., Muscles and Movements. Krieger, New York (1977). E. Y. Chao ,A. Kai-Nan, Y-S Chao, Biomechanics of the Hand: A Basic Research Study, World Scientific Pub Co. (1987). Y.Y.F. Chan and G.K. Stylios, Designing Aesthetic Attributes with Shape Memory Alloy for Woven Interior Textiles, Technical document, Heriot-Watt University, RIFLEX Institute, Galashiels, Scotland. Y.Y.F. Chan, R.C.C. Winchester, T.Y. Wan, G.K. Stylios, The Concept of Aesthetic Intelligence of Textile Fabrics and Their Application for Interior and Apparel, Technical document, Heriot-Watt University, RIFLEX Institute, Galashiels, Scotland. S. Carosio, A. Monero, Smart and hybrid materials: perspectives for their use in textile structures for better health care, Proc. of International Workshop: New Generation of Wearable Systems for e-Health: Towards a Revolution of Citizens' Health and Life Style Management?, Lucca, Italy, 2003, 271-280. A. Mazzoldi, C. Degl’Innocenti, M. Michelucci, D. De Rossi, Actuative properties of polyaniline fibers under electrochemical stimulation, Mat. Sci. Eng. C 6 (1998), 65-72. W. Lu, A. G. Fadeev, B. Qi, E. Smela, B. R. Mattes, J. Ding, G. M. Spinks, J. Mazurkiewicz, D. Zhou, G. G. Wallace, D. R. MacFarlane, S. A. Forsyth, M. Forsyth, Use of ionic liquids for S-conjugated polymer electrochemical devices, Science 297 (2002) 983-987. B. Mattes, Electronic textiles based on intrinsically conducting polymer fiber, Proc. of International Workshop-New Generation of Wearable Systems for e-Health: Towards a Revolution of Citizens' Health and Life Style Management?, Lucca, Italy, 2003, 245-247. R.H. Baughman et al. Carbon nanotube actuators, Science 284 (1999), 1340-1344. M. Zhang, K. R. Atkinson, R.H. Baughman, Multifunctional Carbon Nanotube Yarns by Downsizing an Ancient Technology, Science 306 (2004), 1358-1361. C.P. Chou, B. Hannaford, Measurements and Modeling of McKibben Pneumatic Artificial Muscles, IEEE Trans. On Robotics and Automation 12 no. 1 (1996), 90-102. D. De Rossi, F. Lorussi, A. Mazzoldi, W. Rocchia, E. P. Scilingo, A strain amplified electroactive polymer actuator for haptic interfaces, in Smart Structures and Materials 2001: Electroactive Polymer Actuators and Devices, Y. Bar-Cohen, Editor, Proceedings of SPIE, Bellingham, 4329 (2001), 43-53. R.E. Pelrine, R.D. Kornbluh and J.P. Joseph, Electrostriction of polymer dielectrics with compliant electrodes as a means of actuation, Sens. Actuator A 64 (1998), 77-85. R. Pelrine, R. Kornbluh, Q. Pei and J. Joseph, High-speed electrically actuated elastomers with strain greater than 100%, Science 287 (2000), 836-839.
Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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Flexible Displays on Textiles for Personal Protection Vladan KONCAR and François BOUSSU GEMTEX, ENSAIT Ecole Nationale Supérieure des Arts et Industries Textiles, 9, rue de l'Ermitage, BP 30329, F-59056 Roubaix, France
Abstract. In the first part of this article basic definitions of communication apparel, describing the process of conception and its main components are introduced. Building blocks that have to be used in order to realize these generations of apparel are then mentioned and analyzed from the point of view of textiles. A classification of innovative communicative and intelligent functions attributed to communication apparel is also developed together with three different approaches to camouflage fabrics creation. In the second part of the chapter, a new development methodology of flexible textile display fabric is described. The screen matrix is produced during the weaving process, using the texture of the fabric. A small electronics device integrated into the system controls the LEDs that light groups of fibers. Each group provides light to one “pixel” on the matrix. A specific control of the matrix is then performed by wireless telecommunication services, providing instant access to the downloading of various patterns and cartoons inside the clothing. Initially developed in the field of communicative clothing, this new kind of display can also be applied to any field that requires compact and flexible devices. Moreover, it is also possible to produce large-sized displays using this technology. Various applications are to be considered, namely in the fields of personal flexible displays, camouflage fabric realization and many others. Keywords. Flexible display, Optical fibers, Camouflage
Introduction The armed and security forces have been experimenting with weaving computer and communications technology into uniforms. Future combat dress also might keep soldiers warm or cold and fight off germs, and eventually detect and fight chemical and other dangerous agents. The protective clothing industry plays a crucial role in the protection of firemen, police officers, military personnel, and industrial workers. Concerns for general worker safety, including protection from death and disabling injuries and illnesses, as well as protection from the specific threats of chemical agents and splashes, fire, and bullets, have resulted in an entire industry devoted to personal protective equipment. This equipment includes everything from chemical protective garments and suits to firefighters' turnout gear to industrial fire retardant garments to bullet-resistant vests to respirators. In addition to these changes, the terrorist events of September 11, 2001 and those more recent in Europe have spurred growth in some segments of this industry. While
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this growth is considered to be an anomaly by some industry experts, it is expected to last for at least the next 5 years. The protective clothing industry is undergoing significant growth in many areas as a direct result of the terrorist activities that occurred on September 11, 2001. Tracking and predicting growth related to these events, as well as examining offsetting growth factors, is one of the reasons for doing this study. The soldier could communicate with others either by a fabric keyboard that might be unrolled from the pocket of a uniform, or simply sewn or woven in as part of the uniform's sleeve. On the other side, it is necessary to conceive flexible display and to integrate it in the structure of clothing in order to facilitate different textual and graphic information reading or watching in hostile environmental conditions. If electronics and optical technologies could be integrated successfully into textiles, there could be a striking improvement in battlefield communications. Another interesting and necessary application of security clothing and uniforms is camouflage function. This function may also be generalized to large camouflage fabrics enabling visual protection of larger objects as vehicles, tanks etc. One such project, the Battle Dress Uniform, gives soldiers camouflage and environmental protection, but it also may become a wearable electronic network to send and receive data. In this article the textile fabric obtained by weaving of optical fibers mixed with other textile yarns as cotton, polyester etc. is presented. Then, flexible displays can be created on textiles by producing a screen matrix using the texture of the fabric during the weaving process. A small electronic device that is integrated into the system controls the Light Emitting Diodes (LEDs) that illuminate groups of fibers. Each group provides light to one pixel on the matrix. The dimensions of these structures may be very different. Possible applications are going from personal displays integrated to clothing to large fabrics that may change colors and patterns. Moreover, these displays are very thin and ultra lightweight—two characteristics that could enable many innovative applications as camouflage uniforms. In following section the concept of intelligent apparel is introduced including all building blocks as keyboards, displays etc. Then, several existing approaches to camouflage fabrics are presented in order to situate the problem and to indicate another possible applications of fabrics based on optical fibers. Finally, in the fourth section the principle of optical fiber fabrics is exposed together with weaving technique, the mechanical and chemical treatment of cladding enabling the creation of display matrixes. The connections with LEDs and electronic interfaces are also shown.
1. Intelligent Apparel The term ‘intelligent apparel’ describes a class of apparel that has active functions in addition to the traditional properties of clothing. These novel functions or properties are obtained by utilizing special textiles or electronic devices, or a combination of the two. Thus, a sweater that changes color under the effect of heat could be regarded as intelligent clothing, as well as a bracelet that records the heart rate of an athlete while he/she is exercising. Intelligent clothing can therefore be classified into three categories [1]:
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Clothing assistants that store information in memory and carry out complex calculations; Clothing monitors that record the behavior or the health of the person; Regulative clothing, which adjusts certain parameters, such as temperature or ventilation.
Finally, all intelligent clothing can function in manual or automatic mode. In the case of manual functioning, the person who wears the clothing can act on these additional, intelligent functions, while in the automatic mode the clothing can react autonomously to external environmental parameters (temperature, humidity, light, etc.). 1.1. Communication apparel Communicative clothing can be perceived either as an extension, or as the next generation, of intelligent clothing. Although all clothing communicates intrinsically by virtue of its appearance, the type of communication referred to here is that of information coded and transmitted by means of electronic components in clothing. In addition to the first examples of the integration of portable telephones and miniature PCs, many applications are being studied and have yet to be imagined. Communication can indeed be achieved between clothing and the person who wears it, or between clothing and the external environment and other people. In both cases, ‘communicative’ clothing refers to any clothing or textile accessory that receives or emits information out of the structure that composes it. 1.2. Potential targets and applications Everyone wears clothing, and most people are concerned with the appearance of communication apparel. However, the needs will be different within any given group of people. Let us simply note that the broad, principal topics are: • • • • •
Professionals [2,3] (the need for ‘free hands’ functions, safety, data exchanges); Health care [4] (monitoring, training, remote diagnosis); Everyday life [5] (telephony, wellness); Sports [6,7] (training, performance measurement); Leisure (aesthetic personalization, network games).
1.3. Technical elements enabling the production of communication apparel Previous sections have described communication apparel as an extension of the functionality of intelligent clothing. A study of the various technologies involved in the process of producing intelligent clothing can help to anticipate the new uses and new communication services that could be added to clothing. It is therefore advisable to have a vision of the various techniques likely to confer an unspecified form of intelligence on clothing. In the following sections the building blocks for integration are developed.
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1.4. Various building blocks for integration 1.4.1. Peripherals The main peripherals supposed to be used in communication apparel are mentioned and quickly analyzed in next few paragraphs. 1.4.2. Control interfaces - Near the ‘human interfaces’ The use of clothing as supports of control interfaces is interesting because the control interfaces can be close to the parts of body that are concerned [8,9] for example, earphones in a collar or a bonnet, a microphone in a collar or a keyboard applied to the sleeve of a jacket. Another interesting example is, of course, voice recognition [10-13]. The ergonomic adaptation to clothing of all of these control interfaces is also very important. In contrast to certain miniaturized communicative devices, clothing has a greater surface area, which enables it to offer more functionality. For example, the small keyboard of a mobile phone that fits in the palm of one’s hand becomes much more readable when transposed to the surface of a piece of clothing that is three times larger. On the other hand, the lightness and flexibility that also characterize clothing implies a need to redefine the forms and materials employed for these new interfaces. New properties guaranteeing resistance to wear and to washing must also be taken into account. 1.4.3. Sensors Since clothing accompanies every body movement, and is sometimes in direct physical contact with the person, it has become an ideal physical support for translating and interpreting human activity by means of sensors. Clothing could be used to detect different actions, in particular the recognition of gestures, in order to facilitate certain commands that are intuitive, as with the automatic release of a phone call when one moves the collar of clothing to the ear [14,15]. Moreover, when these sensors are associated with computing and with the control unit, they may allow the recognition of situation and context for a better interpretation of reality. Sensors in communicative clothing could also be used as psychological sensors for various parameters. This term refers to the sensors used to record health or person parameters in a broad sense. The applications rising from the use of these sensors are numerous. We can, for example, use sensors to provide a physical performance analysis of an athlete, or to conduct a patient medical follow-up in real time. 1.4.4. Interfaces of information restitution In many applications, it is necessary to display or reproduce the information produced by communicating systems integrated into clothing. Therefore, traditional interfaces such as displays, screens or loudspeakers have to satisfy the same ergonomics and mechanical resistance criteria as those quoted in the case of control interfaces. Concerning color liquid crystals screens, for example, the aspects of rigidity, weight and consumption, which characterize them at the present time, have to be adapted. Solutions containing micro-screens in glasses or using technologies, including flexible supports, have begun to appear.
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In addition, the proximity of clothing and textile accessories to the natural human senses opens new possibilities for the transmission of information. Visual and auditory ways of collecting information (such as screens and loudspeakers), which are today largely developed because they do not require direct contact with the user, could soon be joined by tactile and olfactory methods. The T-shirt with a collar that translates environments by diffusing a combination of perfumes is about to leave the realm of science fiction. 1.4.5. Data processing The material supports of memory, computation and data processing (RAM, hard disks and processors) will certainly not evolve much in the short term unless they do so in the direction of miniaturization. Even if developments are achieved on flexible substrates, they remain fragile and require partly rigid protection in order to be integrated into communication apparel. However, their integration has become entirely possible, as seen in the incorporation of a micro PC into the loop of a belt. It is also possible to imagine that only a small quantity of information is processed locally in communicative clothing, and that more complex functions and more significant memory capacities are handled by higher-powered remote servers. This difference between local and mass treatment involves the development of specific algorithms, as is the case for intelligent vehicles. 1.4.6. Connectors Connection problems are another major issue in state-of-the-art communicative clothing. The principal question is how to transport information and energy among the various components of the electronic system with optimal efficiency. The concepts of weight distribution and ergonomics must be taken into account in distributing the various components on various zones of the body. Diverse techniques of wireless transmission exist; for example, infrared or radio operator waves using various standards (IEEE 802.11, Bluetooth, etc.). If these modes of transmission are to free communicative clothing from the need for physical connections, several additional constraints must be taken into account. For example, the energy consumption necessary to their operation may be important. Moreover, when it is a question of simple information transport (such as an open or closed contact or something similar) or of energy transport, wired connections become indispensable. The wireless connections mainly have to be used to connect the user to the external environment. In addition, it seems interesting to have only one energy source distributed to the disparate electronic interfaces, thus allowing better energy management. On the other hand, each electronic interface could have its own computation and storage capacities, which would allow resources to be allocated and weight to be distributed. It is important to examine the problem of control and the centralization of information restitution. In fact, to be able to manage all of the functions of a complex communicating device, it is necessary to centralize outgoing controls and incoming information on a single interface. This means that the accessing of emails or a direction on a cartographic site, for example, must be done on a single screen.
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1.4.7. Energy Autonomy in energy is still a main handicap of the majority of mobile electronic devices. Many users of wireless devices have no doubt dreamt of never having to reload their mobile phones. Even if electronic circuits require increasingly less energy, new possibilities appear and create an additional need for energy (a larger screen size implies a need for greater power consumption). Even in the case of communication apparel, autonomy versus weight and volume is once again a compromise that must be made. Battery technologies evolve (e.g., Lithium-Polymer) but, unfortunately, the batteries are still often the heaviest part of portable devices. The advantage of communication apparel is that the weight distribution in clothing will make it possible to be partly freed from this constraint. Another interesting alternative seems to be the use of renewable energy sources. Solar energy and wind are relatively poorly adapted to clothing because they require large surface areas to be truly effective. On the other hand, many studies have been carried out on techniques that will make it possible to recover the energy released by the physical activity of the human body during the day. And, once more, clothing is an ideal support for these new recharging systems. 1.4.8. Conclusion In this chapter, several basic definitions relating to communication apparel from our point of view were given. A classification of functions attributed to traditional apparel, and new innovative functions that should upgrade this traditional apparel to intelligent and communication apparel, were outlined and described. Technical elements enabling communication apparel, including peripherals, data processors, connectors and energy supplies to be produced were then examined and analyzed. Finally, it is important to note the distinction between wearable communication and ‘wearable computers’, which are not incorporated into the clothing itself, but transported as objects. Wearable communication also differs from ‘intelligent clothing’, which reacts to exterior or physiological stimuli to regulate and control the user's wellbeing, like the Vitamin C distributing T-shirt, for example.
2. Camouflage fabrics & apparel Three different existing approaches to camouflage textiles structures are presented in this section. • A multidimensional camouflage outer wear garment system including garments made of various combinations of two-dimensional and threedimensional camouflage material. The two-dimensional and threedimensional camouflage materials are positioned within garments so as to distort the smooth line silhouette of the wearer [16]. •
Digital patterns apparently started in Canada around 1995. The pattern had to be reproduced on fabric with exacting accuracy to ensure integrity of the “pixellation”. This pixellation is a key element of camouflage fabric overall effectiveness [17].
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Optical camouflage is a kind of active camouflage. This idea is very simple. If you project background image onto the masked object, you can observe the masked object just as if it were virtually transparent [18].
2.1. Multidimensional camouflage Zones of three-dimensional material are disposed across limited selected regions of the garments to maintain continuity of silhouette distortion while two-dimensional material is disposed over predefined extended regions adjacent the zones of three-dimensional material as shown in the Figure 1.
Figure 1. Multidimensional camouflage outer wear garment system
A multi-dimensional camouflage outer wear garment system comprising: a jacket portion for covering the torso and arms of a wearer wherein the jacket portion comprises two-dimensional camouflage material arranged in patterned combination with three-dimensional camouflage material to form an outer visible jacket surface, said three-dimensional camouflage material being disposed across a forward shoulder covering region of the jacket portion and across exterior sleeve regions of the jacket portion covering the outer arms of the wearer such that said three-dimensional camouflage material disrupts the silhouette of the wearer, and wherein said twodimensional camouflage material is disposed across a back covering region of the jacket portion such that at least a portion of said back covering region is of substantially flat two-dimensional character. The use of manufactured camouflage material is an extension of the use of natural materials to cause a structure or individual to blend into its natural background and
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escape visual detection. The development of camouflage materials has led to the manufacture of clothing with the same purpose as the use of natural materials, causing the wearer to blend into the natural background with emphasis on vegetation and terrain. For purposes of this invention, camouflage material is divided into two distinct categories: two-dimensional material which is generally flat in profile having a length dimension and a width dimension, but a negligible thickness dimension, and threedimensional material having length, width, and a significant thickness dimension. Twodimensional materials may be made from woven, knit or other fabric constructions as will be well known to those of skill in the art as well as from non-fabric constructions. Although the two-dimensional material may be a solid camouflage color, most frequently the material is dyed or colored in a multi-colored pattern to simulate the pattern and coloration of the terrain and vegetation in which the camouflaged item is to be used. In addition to the benefits of coloration and pattern provided by two-dimensional material, three-dimensional materials provide the additional feature of disrupting the outline or silhouette of an object when viewed from a reasonable distance. Such material not only looks like the native vegetation, but the three-dimensional aspect of the material allows it to move like native vegetation and to disrupt the normal silhouette of the wearer. It is known to create a three-dimensional fabric by utilizing a two layered structure and cutting the exposed outer layer in flaps, loops and similar shapes that simulate the shapes and sizes of natural vegetation, such as leaves, twigs, branches, and open spaces. As will be appreciated, cut pieces create the third, thickness dimension of the three-dimensional camouflage material. 2.2. Digital patterns camouflage fabrics Recently the new Canadian Camouflage pattern CADPAT (Figure 2.) and the U.S. Marines pattern MARPAT (Figure 3.) based on the Canadian developed pattern, have garnered allot of attention as the pattern is made up of a digitized image using four colors. This digital effect generates a dithering effect between colors (no solid lines) and works well within 100 yards of an adversary. However, this advance in camouflage is minimal as the colors tend to blend into each at farther distances, if this blended color of the uniform is different than the background the human shape is revealed at these distances. While CADPAT and MARPAT may be the current top patterns under field tests they still have limitations which can be overcome.
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Figure 2. Canadian Camouflage Pattern
Figure 3. U.S. Marines pattern
What is missing in the new generation digital camouflage is a pattern that works both close and distant, usually there is a tradeoff when choosing a spatial frequency (size of the blotches). Why would an army want to change from Olive Drab (OD) or flat colors, they test well in camouflage research? As good as the flat colors are (OD, Gray or Khaki), they do essentially lack the disruptive element which is crucial when there is available cover, and where ranges of engagement exceed those of built up populated areas. Canadian CADPAT is 30% more effective than Olive Drab in field testing. The CADPAT soldiers could get 30% closer than the minimum ID range for a user wearing OD. What about all the hunting camouflages that use many colors to look almost photo realistic? Camouflages used in most militaries range from 4-6 colors this is due to cost increases with printing additional colors. When making a few 100,000 uniforms each additional color adds huge costs with current printing techniques. Testing by the US Marines on hunting camouflage showed that it worked well in specific regions of similar background but only within those areas, military camouflage was better suited for wider regional applications.
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It is important to notice that while one fighter jet can average over 20 million dollars, camouflage research and development for ground soldiers is one of the most under-funded and overlooked areas in the many nations militaries. Many countries in the past few years have recognized this problem and thrown millions into pattern development. The point of camouflage is tactical effectiveness - not aesthetic appearance. To get around many of the current development limitations a mutifractal patterns have been introduced. A fractal is any pattern that reveals greater complexity as it is enlarged. Fractals describe many real-world objects that do not correspond to simple geometric shapes All fractals are derived from a 'positive feedback loop' when the output is fed back into the system as input and looped over and over. A fern is a good example of a fractal found in nature; the individual leaves on a fern branch are miniatures of the larger leaf and so on... These elusive multifractals for camouflage have now been discovered and patterns have now been developed using a proprietary graphics techniques known as C2G (Camouflage Designated Enhanced Fractal Geometry CDEFG). The results are Advanced "Camouflage Fractures" (Fractal + Nature = Fracture). Several examples of fracture generated patterns are shown in Figures 4 and 5.
Figure 4. Forest 1 and 2 & Desert digital camouflage
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Figure 5. Two different digital camouflage patterns
The problem with the digital or any other types of passive camouflage fabric is that there are many possible patterns in function of environmental conditions. Therefore, it is necessary to have many uniforms and to adapt to different situations. 2.3. Optical Camouflage Optical camouflage is a kind of active camouflage. This idea is very simple. If you project background image onto the masked object, you can observe the masked object just as if it were virtually transparent. This shows the principle of the optical camouflage using X'tal Vision. You can select camouflaged object to cover with retroreflector. Moreover, to project a stereoscopic image, the observer looks at the masking object more transparent. Optical camouflage can be applied for a real scene. In the case of a real scene, a photograph of the scene is taken from the operator’s viewpoint, and this photograph is projected to exactly the same place as the original. Actually, applying optical camouflage to a real scene requires image-based rendering techniques.
Figure 6. Optical active camouflage
How does it work?
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First, putting the video camera behind the person in the cloak, and capturing his background. Then, the captured image is projected onto the cloak from the projector. So, if you see from the peephole, you will see as if the cloak is transparent. Because the image is projected by the technology called Retro-reflective Projection Technology (RPT), you can see the reflection only on the cloak and clearly even in brightness. Cloak’s secret! The special material is used as screen for RPT. That’s different from the screen in the cinemas. This material is called ‘Retro-reflective Material’ (Figure 7), and also used for the cloak. The surface of Retro-reflective Material is covered with very small beads. If the light strikes the material, the light reflects only in the same direction as it has come. So, the image is reflected clearly even in brightness. In fact, you can find a lot of things using Retro-reflective Material around you. Traffic signs, bicycle’s reflector and the lighting part of the raincoat are made from Retro reflective Material. As like the transparent cloak, it can be seen from far away because they shine brightly by little light of the cars.
Figure 7. Retro reflective material
The light scatters in various directions. Retro-reflective Material The light reflects only in the same direction as it has come.
3. Textile based display 3.1. Introduction Several different projects dealing with flexible displays and screen development have been carried out over the past decades. The final objective is to obtain sufficiently bright and flexible displays in order to facilitate their integration into communicative clothing. Different approaches have been developed involving new textile materials or using the optical fibers in the textile structures. These approaches are discussed in the next sections.
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3.2. Textile-based flexible displays Concerning textile-based displays, several approaches exist. The research project developed at Auburn University [19] deals with photo-adaptive fibers for textile materials. Moreover, the aim of this project is to develop photo-adaptive fibers that can undergo photo-induced reversible optical and heat reflective changes. Early on, thin and optically transparent polymer films were prepared to study the kinetics of particle evolution occurring in photosensitive fibers. The films were optimized for speed in metal particle formation and were prepared exclusively at high light intensities. These films will be used to study the chemistry of interfacial regions, which seem to have similar properties to the fibers. This approach will then be generalized to produce photo-adaptive fibers in order to make flexible displays using this type of fiber. Another very interesting research project, in the field of ‘chameleon fibers’, has been developed at Clemson University’s School of Textiles [20]. The aim of this project is to create modifiable color fibers and fiber composite structures. This is supposed to be accomplished by incorporating molecular or oligomeric chromophoric devices capable of changing color over the visible portion of the electromagnetic spectrum into (or onto) fibers. This is done by the application of a static or dynamic electrical field. Deliverables envisioned for this type of material include wall and floor coverings that change color, and also ‘smart’ and communicative clothing with flexible displays. Research on this subject has been conducted in a complementary manner in the laboratories of Furman University, Clemson University and the Georgia Institute of Technology [21]. Color change is due to the absence of specific wavelengths of light, which will vary with the application of an electromagnetic field due to structural changes. Electrically conductive fibers can be used to provide a source for generating the electrical field necessary for color change. Films also have the potential to be applied directly as coatings or polymerized directly on fiber or textile substrates by in-situ processes [22]. The electrical field strength necessary to bring about dynamic color change will depend on the choice of oligomer or molecular species, either attached to the fiber or to the surface of the film or embedded within the matrix of the material. A color change from green to light blue has already been demonstrated for a film containing an oligomeric species in a small applied electric field. A Visson company has also recently developed display prototypes based on a 0.2 mm thin textile fabric [23]. The display is an assembly of wire conductors woven in an X –Y structure, in order to create a rows-and-columns electrodes network. Each one of these conductive fibers is covered with a very fine layer of electro-luminescent material. By addressing an electric voltage to one column and one row simultaneously, the electric field created at the intersection of the corresponding fibers causes electroluminescent material to be emitted at this point. Some interesting studies also deal with nanocomposite fibers that could be used to develop the flexible displays. The project is the development of biphasic fibers with properties that leapfrog those of the matrix polymers. For example, the improved hightemperature mechanical performance, useful optical properties, and electrical or barrier properties of these fibers will have a major impact on titre reinforcement, electrooptical devices and other applications [24].
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3.3. Optical Fibers in Textiles Optical fibers are currently being used in textile structures for several different applications. They are first often used as sensors exploiting the Bragg Effect. At The Hong Kong Polytechnic University, X. Tao has developed several very important applications using optical fibers to measure strain and temperature in composite structures [25-28]. These fiber optic sensors have also been used in smart textile composites [29]. Actually, fiber optic Bragg grating sensors are attracting considerable interest for a number of sensing applications [30, 31] because of their intrinsic and wavelength-encoded operation. There is great interest in the multiplexed sensing of smart structures and materials, particularly for the real-time evaluation of physical measurements (e.g., temperature, strain) at critical monitoring points. In order to interrogate and demultiplex a number of in-fiber Bragg grating sensors, whether or not they are in a common fiber path, it is necessary that the instantaneous central wavelength of each sensor can be identified. S. Jayaraman [32] research team at Georgia Tech developed a smart shirt called the Georgia Tech Wearable Motherboard that uses optical fibers to locate the exact position of a bullet’s impact. Among other interesting functions, this property of location enables a soldier or policemen to carry out health and vital function analysis in a combat situation. In the present study, optical fibers in textile structures are used to create flexible textile-based displays based on fabrics made of optical fibers and classic yarns [33-38]. The screen matrix is created during weaving, using the texture of the fabric. Integrated into the system is a small electronics interface that controls the LEDs that light groups of fibers. Each group provides light to one given area of the matrix. A specific control of the LEDs then enables various patterns to be displayed in a static or dynamic manner. The basic concept of flexible display is described. It includes the weaving phase, the optical fiber processing procedure that creates the pattern matrices, the electronics interface that controls these matrices, and several applications of flexible displays. The two main interesting characteristics of this new flexible device are its very thin size and the fact that it is ultra lightweight. This leads one to believe that such a device could quickly enable innovative solutions for numerous applications.
4. Optical Fiber Flexible Display (OFFD) Flexible displays can be created on textiles by producing a screen matrix based on the end and pick densities of the fabric. A small electronic device that is integrated into the system controls the Light Emitting Diodes (LEDs) that illuminate groups of fibers. Each group provides light to one pixel on the matrix. These displays are very thin and ultra lightweight—two characteristics that could enable many innovative applications. Although initially developed for clothing, the displays could be used to exhibit information or designs in cars, portable electronic devices and even houses and buildings. Indeed, research on the design and development of flexible displays based on processed optical fibers has opened up new frontiers in fashion, public safety, automotive equipment and home furnishing. In this section, the process to design and realize an optical fibers flexible display is discussed in detail.
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4.1. Weaving Optical Fibers Poly(methyl methacrylate) (PMMA) optical fibers possess a rigidity and fragility that make them different from most traditional textile fiber threads and filaments. With regard to section diameter, a good compromise must be reached: A diameter that is too large can cause inflexibility, while a too-small diameter induces a low shear resistance and loss of light intensity. We used fibers with a diameter of 0.5 mm to make the first prototypes. We have also conducted tests on fibers with a diameter of 0.25 mm, but further developments in the process of weaving are still required to ensure sufficient fabric resistance in bending. Weaving takes place on a traditional two-dimensional looms (manual and automated) shown in Figure 8 modified in order to make possible automated introduction of optical fibers mainly in the weft direction.
Figure 8. Manual Shuttle hand-weaving loom (ARM) and Automatic Rapier weaving loom (Dornier)
The optical fibers can be woven in two directions (warp and weft) in addition to other kinds of yarns. Therefore, it is theoretically possible to obtain an optical fiber XY network. However, this would present several disadvantages: • • •
The grid (and, hence, the resolution) would not be very dense and the fabric would be extremely rigid because of the relatively high radius of curvature of optical fibers. Constituting a warp beam of optical fiber is very long and very expensive. The resolution would be tiny.
It is also possible that a three-dimensional structure in weaving would not bring any significant advantages except in the case of specific camouflage structures.
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Thus, our initial plan was to develop a fabric comprising optical fibers for picks and silk yarns for ends. Other natural, artificial or synthetic yarns could also have been used to constitute the warp. Warp threads must be significantly chosen with the aim of achieving good flexibility in the fabric, fine count yarn and an improved capacity to diffuse and reflect the light emitted by optical fibers for better legibility of information. An example of an optical fiber fabric display (OFFD) using a specific weaving diagram is shown in Figure 9. Different textile finishing methods are being tested—either in printing or in coating—to guarantee grid stability and flame resistance and to enable optimal light emission intensity and contrast.
Figure 9. Part of OFFD weave diagram
4.2. Display Matrix Design The screen for fabric displays comprises a number of surface units, or pixels; each one can be illuminated by a light source emitted from one side of the fabric by one or several PMMA optical fibers with discrete index variation. The pixels are directly formed on optical fibers while transversely forming a spout of light on the fabric. The process consists of generating micro-perforations that reach into the core of the fiber (Fig. 10). The remainder of the optical fiber, which did not receive any specific processing, conveys the light without being visible on the surface.
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Figure 10. Treated optical fiber
Two processing techniques have been developed for optical fibers. The first is a mechanical treatment using the projection of micro particles with different velocities on the optical fiber’s cladding. The result is presented in Fig. 11. The second technique uses different chemical solvents to make these micro perforations; this method seems to produce a better final result. (A chemically processed cladding surface is shown in Fig. 12). Finally, Figure 13 shows the chemically processed fiber surface picture obtained by a scanning electron microscope.
Figure 11. Micro perforation in of cladding obtained by mechanical treatment (AFM image)
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Figure 12. Micro perforation in of cladding obtained by chemical treatment (AFM image)
Figure 13. SEM image of optical fiber surface, chemical treatment
The difference between the light intensities of mechanically and chemically treated optical fiber fabric is shown in Figure 14. There are three methods that are used to light ON and OFF static patterns on the fabric (texts, logos and scanned pictures), which we adapted to develop our own technique. A basic fabric is used in the first method. The lighting zone to be processed, which is composed of optical fibers, is delimited by a stencil key. The picture remains static—with eventual color changes—but can offer quite a high resolution.
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Figure 14. Light intensity - Chemically treated OF Fabric (top) and mechanically treated OFF (low)
In the second method, the area to be lit is formed during weaving on a Jacquard loom before being processed. The remaining, inactive fabric is composed of the floating fibers on the back of the fabric. A third method uses a two-layer adapted basic-velvet fabric that makes optical fibers as visible as possible, but with sufficient consistency of fabric structure. Prior to the weaving process, the optical fibers are chemically treated, enabling the specific dynamic lighting areas to be created. We modified these techniques by creating specific weaving diagram and an adapted lighting control in order to generate variable information on the same fabric area. We developed a matrix that makes it possible to display a great deal of basic information, such as texts, logos or other patterns, in a static or dynamic way. Because a fabric display can only be produced by columns made of a single optical fiber or group of fibers, we had to create lines artificially. Similar to the process that would be used with two superimposed patterns to be lightened on the same column, this involves alternating two consecutive weft fibers—one for the first pattern, and the other for the second. Each is processed on a precise section in order to re-emit light at a specific place. The principle is the same for three superimposed patterns, except that one fiber is taken out of three for each pattern. When the weaving is sufficiently tight, a visual impression is given of full, enlightened zones. Chain wires will be able to help diffuse the light toward the dark zones between lightened segments. The number of rows to be produced seems limited by the technique, insofar as, on the same unit area, more dark areas are produced than lightened ones. The appreciation of the definition will then be based on the size of the pixels and the screen, in addition to the distance from which people watch the screen. Various light sources can be used to feed the matrix. The choice mainly depends on the number of fibers connected to each source and the level of power consumption. For the first prototypes, we used high luminous LEDs that are 3 mm in diameter. LED technology has many advantages, as diodes can be easily driven by electronics under low voltages (2V to 4V, depending on the color). Therefore, many “light effects” can be generated on the display, such as flashing or varying the intensity of the light, providing all kinds of animated movies. Figures 15 and 16 show two different OFFD. These displays have been realized in collaboration with France Telecom® Company. They are each made using 0.5 mm and 0.25 mm diameter optical fibers. Each pixel is composed of four fiber segments and is controlled by one LED located in the lining of the cloth, on one side of the OFFD. The color of the pixels is determined by the corresponding LEDs.
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Figure 15. Flexible display, LED connected to fabric
Figure 16. Flexible display – Jacquard weaving
OFFDs offer another possibility: Although the definition is limited to the number of rows, it is possible to repeat on fabric the same line of characters or patterns in the direction imposed by optical fibers. The fixed or animated pattern reproduction can be used for purely decorative applications; for example, to create a tapestry adapting its colors to the clothes worn by the occupants of a room. 4.3. Implications and Applications Optical fiber screens provide access to simple and animated visual information, such as texts or pictograms. It is possible to download, create or exchange visuals via the appropriate Internet gateway. Conceivably, images or text could be sent using wireless technology from a computer or a mobile Internet terminal to an article of clothing.
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The main functions of the new prototypes related to textiles and apparel for personal protection are: • • • •
To “be seen,” for security (flashing light on security clothing, www.vfic.net, see Figure 17); To facilitate communication in dangerous environmental conditions; To help organization and to synchronize actions; To realize camouflage patterns in function of external conditions (wood, desert, streets …) .
OFFDs can also be used as displays for mobile phones, PDAs (personal digital assistants), wearable computers and other portable electronic devices.
Figure 17. Flashing lamp for security clothing
There is also enormous potential for firefighting and police applications. For example, information and warnings could be displayed on clothes—which could both increase public safety and help officers and firefighters to operate in remote and challenging conditions. Concerning camouflage applications, many possibilities have to be explored involving traditional camouflage fabrics combined with OFFDs that may adapt in function of environmental conditions. In this digital age, information is virtually everywhere and a multitude of screen and display technologies will be necessary to keep up with the demand. OFFDs have shown great promise as a new and interesting way to present images and information.
5. Conclusion and Future Investigations The existing technologies on the weaving and specific processing of optical fibers have been adapted by creating a matrix within the fabric and an accordingly developed electronic control network of LEDs to produce an extremely fine, flexible and bright textile display. The structure and the textile materials used suggest a new approach in
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the field of displays, and more particularly, flexible displays. Generally, textiles have all the basic tools, which are suitable, to enable the creation of new designs and new apparatuses that will lead to new solutions for specific applications. It is obvious that information is virtually everywhere and that screens and displays have to adopt a multitude of technologies and forms dedicated to targeted applications in public or private places. For this reason, bright optical fiber fabric displays have a significant role to play, particularly in the field of very large-sized flexible displays. Acknowledgements We would like to thank Dubar Warneton [39], Cédric Brochier Soieries [40] and Audio Images [41] for their contribution to the development of the Optical Fiber Fabric.
References [1] V. Koncar, B. Kim, E. B. Nebor, X. Joppin Intelligent Life Clothing - FICC (Floatable Intelligent and Communicative Clothing) Project, proceedings of 8t International Symposium on Wearable Computers, in Arlington, VA (Washington DC metro area) USA, October 31 - November 3, 2004. [2] Bauer M, Kortuem G, Segall Z, Where are you pointing at? A study of Remote Collaboration in Wearable Videoconference system, proceedings of 3rd International Symposium on Wearable Computers, San Francisco, USA, IEEE, 18-19 October 1999. [3] A. Smailagic, D. Siewiorek, D. Bass, B. Iannucci, A. Dahbura, S. Eddlesto, B. Hanson, E. Chang, ‘MoCCA: A mobile communication and computing architecture’, proceedings of 3rd International Symposium on Wearable Computers, San Francisco, USA, IEEE, 18-19 October 1999. [4] Vital Signs Monitor, Fitsens, http://www.fitsense.com/, FitSense Technology21 Boston Road, PO Box 730, Southborough, MA 01772 [5] J. Yang, X. Yang, M. Denecke, A. Waibel, Smart sight: A tourist assistant system, proceedings of 3rd International Symposium on Wearable Computers, San Francisco, USA, IEEE, 18-19 October 1999. [6] J. Farringdon, A. J. Moore, N. Tilbury, J. Church and P. D. Biemon, ‘Wearable Sensor Badge and Sensor Jacket for Context Awarness’, proceedings of 3rd International Symposium on Wearable Computers, San Francisco, USA, IEEE, 18-19 October 1999. [7] Sangle-capteur de Polar, http://www.randburg.com/fi/polarele.html, Polar Electro Oy Professorintie 5, FIN-90440 Kempele, Finland [8] Z. T. Hon, A. Pentland, ‘Tactual displays for wearable computing’, The Medialab Massachusetts Institute of Technology, proceedings of 1st International Symposium on Wearable Computers, Boston, USA, IEEE, 18-19 October 1997. [9] B. Thomas, K. Grimmer, D. Makovec, J. Zucco, B. Gunther, Determination of placement of a body-attached mouse as a pointing input device for wearable computers, 3rd International Symposium on Wearable Computers, San Francisco, USA, IEEE, 18-19 October 1999.
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[10] A. Vardy, J. Robinson, L. T. Cheng, The WristCam as input device, proceedings of 3rd International Symposium on Wearable Computers, San Francisco, USA, IEEE, 18-19 October 1999. [11] Project: the Spyglass: an interface for I-wear, I-Wear Consortium Meeting, Brussels, Belgium, Starlab, 30-35, 6-7 June 2000. [12] G. Cleveland, L. McNinch , Force XXI land warrior: Implementing spoken commands for soldier wearable systems, proceedings of 3rd International Symposium on Wearable Computers, IEEE, 18-19 October 1999. [13] A. Smailagic, D. Siewiorek, R. Martin, D. Reilly, CMU wearable computers for real-time speech translation, proceedings of 3rd International Symposium on Wearable Computers, San Francisco, USA, IEEE, 18-19 October 1999. [14] J. Kangchun Perng, B. Fisher, S. Hollar, K. S. Pister, Acceleration sensing glove, proceedings of 3rd International Symposium on Wearable Computers, San Francisco, USA, IEEE, 18-19 October 1999. [15] V. R. Pratt, Thumbcode: A Device-Independent Digital Sign Language, Stanford University Report, USA, July 1998, http://wearables.stanford.edu [16] J. C. Egnew, Multidimensional camouflage outer wear garment system, U.S. Patent 6,499,141, December 31, 2002 . [17] G. Cramer, President HyperStealth Biotechnology Corp, http://www.hyperstealth.com/CADPAT-MARPAT.htm. [18] S. Tachi, Telexistence and Retro-reflective Projection Technology (RPT), Proceedings of the 5th Virtual Reality International Conference (VRIC2003), pp.69/1-69/9, Laval Virtual, France, May 13-18, 2003. [19] G. Mills, L. Slaten, R. Broughton, K. Malone and D. Taylor, Photoadaptive Fibers for textile Materials, National Textile Centre Research Report M98-A10, Volume 8, November 2000. [20] R. V. Gregory, R. J. Samuels and T. Hanks, Chameleon Fibers: Dynamic Color Change From Tunable Molecular and Oligomeric Devices, National Textile Centre Research Report M98-C1, Volume 8, November 2000. [21] R. V. Gregory, W. C. Kimbrell and H. H. Kuhn , Synth Met, 28, 1&2, 1989, c823. [22] T. R. Skotheim, R. L. Elensbaumer, Reynolds, Handbook of Conductive polymer, 2nd ed., Portland, OR, Marcel Dekker, 1998. [23] Visson Israel Ltd.1 Bezalel Street, Ramat Gan 52521, Israel, www.visson.net. [24] Y. K. Kim, S. Warner, A. Lewis and S. Kumar, ‘Nanocomposite Fibers’, National Textile Centre Research Report M00-D08, Volume 8, November 2000. [25] C. W. Du, X. M. Tao, Y. L. Tam and C. L. Choy, ‘Fundamentals and Applications of Optical Fiber Bragg Grating Sensors to Textile Composites’, Journal of Composite Structures, 1998, Vol.42, No.3, 217-230. [26] L. Q. Tang, X. M. Tao, W. C. Du and C. L. Choy, Reliability of Fiber Bragg Grating Sensors in Textile Composites, J. Composite Interfaces, 1998, Vol.5, No.5, 421-435. [27] W. C. Du, X. M. Tao and H. Y. Tam, ‘Fiber Gragg Grating Cavity Sensor for Simultaneous Measurement of Strain and Temperature’, IEEE Photonics Technology Letters, 1999, Vol.11, No.1, 105-107. [28] X. M. Tao, ‘Integration of Fiber Optic Sensors in Smart Textile Composites Design and Fabrication’, J. Text. Inst., 2000, 91, Part 1, No.2.
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[29] D. A. Jackson, A.B. Ribeiro, L. Reekie, J. L. Archambault, and P. St. Russell, Simultaneous interrogation of fiber optic grating sensors. Proc.OFS'9, Florence, Italy, 1993. [30] A. D. Kersey, M. A. Davis, and W. W. Morey, Quasi-distributed Bragg-grating fiber-laser sensor, Proc. OFS'9, Florence Italy, 1993, postdeadline paper PD-5. [31] M.G. Xu, L. Reekie, Y. T. Chow, and J. P. Dakin, ‘Optical in-fiber grating high pressure sensor’, Electron. Lett., 1993, 29, (4), 398-399. [32] S. Jayaraman, ‘The first fully computerized clothing: A higher quality of life through technology’, 2nd International Avantex Symposium, Frankfurt, Germany, 2002. [33] E. Deflin, V. Koncar, ‘For communicating clothing: The flexible display of glass fiber fabrics is reality’, 2nd International Avantex Symposium, Frankfurt, Germany, 2002. [34] E. Deflin, A. Weill, V. Koncar, H. Vinchon, ‘Bright Optical Fiber Fabric – A New Flexible Display’, Proceedings of The 6th Asian Textile Conference, 22-24 Août 2001. [35] F. Veyet and V. Koncar, ’Innovation Textile : Les parapluies intègrent les écrans lumineux’, Rapport de Projet de Fin d’Etudes, ENSAIT, Roubaix, France, June, 2002. [36] V. Koncar, Optical fiber fabric display – OFFD, Optics & Photonics News, The Optical Society of America, April 2005, pp 40-44. [37] A. Bernasson and H. Vergne, Optical Fiber with Multiple Point Latéral Illumination, International Patent no. PCT/FR94/01475, 1998. [38] E. Deflin, A. Weill, G. Ricci, J. Bonfiglio, Dispositif lumineux comprenant une multiplicité de fibers optiques optiques à segments lumineux, brevet n°0102623 déposé en France par France Télécom le 27/02/01 [39] H. Vinchon, Dubar Warneton, 136, rue Jules Guesde B.P.189, 59391 WATTRELOS CEDEX – FRANCE, http://www.dubar-warneton.com [40] Cedric B, Soieries 33, rue Romarin 69001 LYON, http://www.cedricbrochiersoieries.com [41] A. Bernasson, Sarl AUDIO – IMAGES, Parc Ind. du Maréchat, 2 rue A. Einstein, 63200 RIOM – France, http://www.excel-ray.com
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Conductivity Based Sensors for Protection and Healthcare Lieva VAN LANGENHOVE 1 and Carla HERTLEER Ghent University, Department of Textiles, Belgium Abstract. Conductive fibres have become available over the last years. Arranging them in different ways in textile structures can provide several functionalities to the textile material, like sensing. This paper will give an overview of the principles on which such sensors can be based. The sensors should have a full textile character, including resistance against multiple deformation and laundry. Research shows that for many textile structures the sensor capacity decreases during use.
Introduction Smart textiles are an emerging area in textiles. They allow monitoring on a permanent base without affecting the comfort of the person wearing them. They will generate a real breakthrough in the area of protection and healthcare. Indeed increase of risks can be detected in the earliest possible phase, allowing a fast and adequate reaction. Consequently it will become an important tool in view of prevention. However, many problems need to be solved before such smart systems will be actually on the market. At this moment, the materials are not always good enough in several aspects, current data processing techniques do not allow full extraction of the information, long term behaviour is poor. Extensive multi-disciplinary research is required to solve all these aspects.
1. Smart Textiles 1.1. Why Textiles? The first question we should ask ourselves is why we would use a textile structure as a carrier for intelligence.
1
Corresponding author: Lieva Van Langenhove, Ghent University, Department of Textiles, Technologiepark 907, 9052 Gent (Zwijnaarde), Belgium, E-mail:
[email protected].
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Although not of prime importance for all applications textile materials as such show a vast number of clear advantages: • • • • • •
They are omnipresent, everybody is familiar with them They are easy to use and to maintain Clothes have a large contact with the body They make us look nice They are extremely versatile in terms of raw materials used, arrangement of the fibres, finishing treatments, shaping etc. They can be made to fit
Typical applications where textile structures are to be preferred are: • • • •
Long term or permanent contact without skin irritation, Home applications, Applications for children: in a discrete and careless way, Applications for the elderly: discretion, comfort and aesthetics are important.
1.2. Functions of Smart Textiles The functionalities of smart textiles can be classified in 5 groups: sensoring, data processing, actuation, communication, energy. At this moment, most of the progress has been achieved in the area of sensoring. Many type of parameters can be measured: • • • • • • • • • • •
Temperature Biopotentials: cardiogram, myographs, encephalographs Acoustic: heart, lungs, digestion, joints Ultrasound: blood flow Biological, chemical Motion: respiration, motion Pressure: blood Radiation: IR, spectroscopy Odour, sweat Mechanical skin parameters Electric (skin) parameters
Some of these parameters are well known, like cardiogram and temperature. Nevertheless, permanent monitoring also opens up new perspectives for these traditional parameters too. Indeed today evaluation is usually based on standards for global population groups. Permanent monitoring supported by self learning devices will allow the set up of personal profiles for each individual, so that conditions deviating from normal can be traced the soonest possible. Also diagnosis can be a lot more accurate.
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Apart from the actual measuring devices data processing is a key feature in this respect. These type of data are new. They are numerous with multiple complex interrelationships and time dependant. New self learning techniques will be required. The introduction of such an approach will be slow, because no evidence of the benefits are available at this moment. “We don’t measure because we don’t know the meaning, we don’t know the meaning because we don’t measure”. Actuation is another aspect. Identification of problems only makes sense when followed by an adequate reaction. This reaction can consist of reporting or calling for help, but also drug supply and physical treatment. A huge challenge in this respect is the development of high performance muscle like materials. 1.3. Smart Textiles for Health Care and Protection As stated in previous chapter, the potential of smart textiles for health care is still largely unexploited. A particular application area is public health. Researchers warn for world wide epidemia. In the past particular types of flue have caused enormous casualties. With our society of huge mobility pandemic diseases will spread far quicker than ever before. Smart textile suits can play a role in remote monitoring, diagnosis and advanced protection. For protection, very smart textile materials can play a role in many aspects. Also the textile can react when necessary, in a passive way or by active control mechanisms. Passive protection systems as are being used today usually have an important impact on comfort, aesthetics and freedom to move. Just look at fire suits where the insulation level is so high that the firemen fade because of overheating caused by their own body heat, irrespective of the external fire. Or hip protectors for the elderly that make people look like M. Michelin. So in general smart clothes offer the possibility of adapting itself to the environment, allowing to provide protection only when required, for instance when temperature is too high, when harmful chemicals or micro-organisms have been detected and so on. The smart suit can detect increased risk and react on it in order to prevent accidents to take place. It can protect against hazards and assess the impact of accidents. Consequently it can provide instant aid as well as long term support to rehabilitation. 1.4. Networks and Organizations: Structure, Form, and Action Let’s look at a scenario for protecting against falling. The suit will help to avoid risky situations. The suit detects a person has an increased risk on falling. It sends out a warning in order to inform the person and his relatives. The suit can supply drugs should this be necessary. It communicates with the house in order to switch on the light when entering a room. It informs objects are lying on the ground. Integrated artificial muscles help to maintain one’s equilibrium. When detecting an actual fall, the suit instantaneously turns into an impact absorbing material.
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After the fall, it assesses whether help is needed. It calls for help and sends out information on the situation. It treats wounds and provides a splint should this be necessary. It provides help to rehabilitation, for instance by stimulating the healing process or by keeping the body in shape during immobilization. And all this in a discrete way, without any special care or loss of comfort. In case of fire men heat protection is required only a very small fraction of time. So the self adapting heat protection level considerably contributes to comfort during most of the operations. However the real threat is the sudden stroke of heat. A smart suit can help to follow up adequately when the risk is rising and it’s time to go. Such a suit is equipped with several sensors at different positions on the body and inside the suit. This allows adequate follow up of the status of the person but also of the suit. As a result the intervention time can be prolonged without loss of safety. Drivers’ attention can be monitored and actions can be taken before accidents happen. Here the main challenge is to identify relevant body information from which attention can be calculated in a quantitative way.
2. Conductive Fibres and Fibrous Materials 2.1. Conductive Fibres Polymer materials and fibres in particular do not conduct electrical currents. They are considered to be insulating materials. Metallic fibres on the contrary show good conductivity. Conductive polymers have been developed quite some time ago, but unfortunately their conductivity is low as compared to real conductors like cupper. Polyanilin, polythyophene and polypyrole are such polymers. The levels of conductivity are illustrated in table 1. Table 1. Volumetric resistance of various conductive fibres.
Fiber Silver Copper Stainless steel Carbon Polymers PANI (panion™) PA charged with nanoparticles
Volumetric resistance (ohm.cm) 1.63 · 10–6 1.72 · 10–6 72 · 10–6 from 2.2 · 10–4 till 10 · 10–3 10–2 – 10–3 10–3 6.5 · 10–4
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Not only the conductivity of so called conductive polymeric fibres is limited, they also have poor mechanical properties and therefore they are usually applied on a textile substrate [1]. Some of the problems with current conductive fibres: • • • •
Conductivity of polymers is not so good, as well as long term stability; they are slightly harmful Metal and metallised fibres are expensive; their mechanical properties are quite different from polymeric fibres Some fibres have dark colour (metallic, carbon) Adding conductive particles may considerably affect on processing and/or fibre properties [2]
Electro-conductive fibres are used on a large scale for a variety of functions: antistatic applications, electromagnetic shielding (EMI), electronic applications, infrared absorption, protective clothing in explosive areas, etc. Their use as a sensor however is a rather new field of application. 2.2. Conductive Fibrous Structures Arranging conductive fibres in a structure like textiles generates a material with a complex behaviour in terms of conductivity. Fibre length being limited, the electron flow has to be transferred from one fibre to the other, from one yarn to the other. Contact resistance between fibres plays a determining role here. Contact resistance usually is quite high as compared to the intrinsic conductivity of the material. Any rearrangement of the fibres in a textile may affect the global conductivity of the structure. It changes the contact resistance, number of contact points, path followed by the current For some applications this is a source of error, for other it is the base of sensor properties.
3. Fibrous Sensors 3.1. Fibre Sensors Conductive fibres show piezo-resistive effects. By extending the fibres, fibre cross section is reduced causing the electrical resistance to go up. Secondly the fibre length increases again causing resistance to increase. As a result resistance becomes an indicator of its extension. However, the level of this type of piezo electric effect is insufficient to allow accurate readings.
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Additional piezo electric effects have to be achieved using other principles. Such principles for instance exploit mechanisms of conductivity as described by Mattes [3]. Further on inclusion of conductive nanoparticles can generate piezo-electric effects, as conductivity will depend on the distance between the nanoparticles [4]. This distance will change due to fibre extension. 3.2. Fibrous Textile Structures Conductive fibres are being used as passive sensors for monitoring biopotential, mainly heart rate. Several research projects have been carried out on this topic [5,6,7,8]. The feasibility has clearly been demonstrated, although the sensor needs to be optimized and practical problems need to be solved (table 2).
Table 2. Textile electrodes for measuring heart rate.
Name Smartex Intellitex VTAM Wearable motherboard
Application Health care Children’s health care Health care Health care, military
Level of transformation Woven/knitted textile sensors Knitted textile structures, textile antenna Partly textile structures Partly textile structures
As explained in paragraph 1.2 and 2.1 several mechanisms cause the resistance to go up or down due to extension of the material. The global effect of these combined mechanisms depend on the type of material and its structures. The conductivity of the textile materials for applications as passive sensor, should be as consistent as possible, so their piezo-resistive effect is a source of error. This can be achieved by careful selection of fibre type and proper design of the textile structure. The resistance of such a structure is constant when for instance a cyclic extension is applied as a simulation of the breathing movement (fig. 1).
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Figure 1. Textile structure without piezo-resistive effect.
On the contrary the same piezo-resistive effect makes the textile a versatile tool for a broad range of sensor applications where extension is a crucial parameter. This is the case for instance for respiration measurements (expansion/contraction of the chest), all kinds of movements (dance, sports, …) as well as volumetric changes like volume of inhaled air. 3.3. Smart Textile Structures The applications mentioned in the previous section are rather straightforward. Careful design of the textile structure enables more advanced sensing properties. The basic mechanisms are related to conductivity, changes in conductivity, currents or change in currents and so on. Any mechanism that affects such parameters is useful. Electrochemistry is an extremely important discipline in this respect. A set of fibres, yarns or fabrics separated one way or another can be considered as a double electrode system. Such a system can be used to detect water. The presence of water will be reflected in an increase of conductivity between the two electrodes. The increase will be bigger when the water contains salt. The reaction of such a textile sensor (i.e. resistance as a function of time), consisting of 2 conductive yarns, on wetting with water with different salt concentrations is given in fig. 2 [9].
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R (Ohm)
5,00E+05
4,00E+05
3,00E+05
2,00E+05 3 1,00E+05 1 2
0,00E+00 -4
-2
0
2
4
6
8 normalized t
Figure 2. Decrease of electrical resistance due to wetting of the sensor.
Impedance spectroscopy has been used to optimize the test set up. A double set of such a 2-electrode system of which one is coated with a coating that is impermeable to the salt but permeable to water allows separation of the quantity of water and the quantity of salt. Coatings with selective permeability can be the base for a huge number of specific sensors, for instance for a qualitative as well as quantitative analysis of sweat. This basic method is suited for a huge range of applications, provided the right electrode configuration, measuring conditions and textile configuration are selected. Electrode configuration for instance includes diameter of the fibres or yarn electrodes and distance between the electrodes. Another approach to design conductive fibre based sensors is based on the piezoresistive effect, whereby the separation of conductive (nano)particles is not achieved by fibre extension, but by fibre swelling. In this case as well one basic technology is capable of generating an enormous range of sensing capabilities. Selection of adequate polymeric materials for the fibres or inclusion of swelling components like gels must be adapted to the triggering agent. In addition coatings with selective permeability can be applied to increase selectivity and specificity of the sensor system. These are just two examples of relatively simple systems with an enormous range of applicability.
4. Strain Sensors The main advantage of smart textiles, sensors or actuators, is that textile materials in general are common products that are comfortable materials that are easy to use. Thanks to these properties it becomes possible to wear the sensors and actuator in an imperceptible way.
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Of course the smart character of the textile should not affect these advantages. Experience shows that two problems arise. The first is the flexibility that on the one hand it is necessary for achieving a good level of comfort, but on the other hand enables multiple deformation of the material. The other are chemical effects. Laundry for instance combines multiple deformation and chemical effects. 4.1. Physical Effects Conductive fibres often have mechanical properties that are quite different from those of “regular” textile fibres. This causes them to react differently to deformation, bending, extension. As a result a slow but consistent migration of those fibres occurs. This eventually leads to separation of both components and this effect may become clearly visible after long term use as for instance breathing sensor (fig. 3).
Figure 3. External loops formed by stainless steel yarns due to repeated extension.
This effect is obviously not welcome because of several reasons: • •
It negatively affects the aesthetic aspect of the fabric It may affect the sensor function
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• •
Contacts may occur with the skin or the environment, leading to false signals, increased noise etc. Fabric feel may be affected
Rearrangement of the fibres happens mostly in the initial phase of use. As a result resistance of a fabric will experience its fastest changes at the beginning of deformation tests later on it will stabilize more or less (Fig. 4).
Figure 4. Change of resistance of a conductive yarn during initial phase of use.
4.2. Fibre Breakage Apart from the quite obvious macroscopic effect described in previous paragraph more complex phenomena influence the sensor function of textile sensors. Stainless steel fibres for instance are rather brittle, so repeated extension and bending will cause them to break. Consequently, the number of fibre to fibre switches will increase with each fibre breakage and contact resistance being the biggest resistance by far, overall resistance of the textile structure will drastically increase. Particularly during laundry deformation is quite intensive, and laundry is of course a very relevant operation so it is a good way to test on impact of defeormation. Measuring changes in length of fibres in an actual textile structure is very difficult, because the fibres are embedded in the textile structure and its unraveling may cause more fibres to break. Fibres may also be crimped considerably so the length measurement in itself gets difficult. An indirect method to evaluate fibre length is yarn strength as this relationship has been demonstrated in numerous studies (fig. 5).
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19,0
Mean of Force_N
18,0
17,0
16,0
15,0 0
5
10
25
Washing cycles
Figure 5. Influence of repeated extension during washing on yarn strength as a measure of fibre breakage.
Mechanical damage of fibres has also been reported by Tao [10]. This work describes the appearance of cracks at the surface of PANi and PPY coated fibres at extensions from 6% onwards. It is quite clear that all factors that affect the conductivity of the material, also affect its proper functioning in the intelligent textile (Fig. 6). Mechanical damage due to multiple deformation in general is an important problem for all kinds of conductive textile materials. Also interconnections between different components (sensors, actuators, electronics, battery, wires) have been reported in many studies as weak spots, in particular at places where soft (textile) and hard (electronics) elements are connected.
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1,20
Mean of lnResistance
1,10
1,00
0,90
0,80
0,70
0,60 0
10
25
Washing cycles
Figure 6. Effect of fibre breakage due to multiple deformation on yarn resistance.
4.3. Resulting Long Term Behaviour of Textile Strain Sensors As explained before several factors may affect the proper sensor function of textile strain sensors. To test this a cyclic loading was applied whilst measuring the resistance of the textile structure [11]. This resistance should go up and down with extension and the amplitude should be high enough for an accurate sensor (Fig. 7).
Figure 7. Variation of resistance due to cyclic loading of the textile strain sensor.
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For many textile structures this amplitude slowly goes down turning the textile material into an unreliable sensor (fig. 8).
Figure 8. Loss of sensor capacity due to multiple deformation.
Surprisingly the amplitude temporarily increases after washing. This is probably due to a sort time rearrangement of the fibres after washing following the considerable fibre rearrangement during washing. (Fig. 9).
Figure 9. Effect of washing on sensor capacity of a textile material.
So the sensor sensitivity of some textile structures actually improves due to washing. This can be represented by expressing the amplitude relative to the value of the actual resistance, for instance at the maximum extension (Fig. 10).
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Figure 10. Impact of washing on textile strain sensor sensitivity.
It can be concluded that textile structures behave in a very complex way as sensor. Depending on the actual fibre type and the fabric structure a wide range of responses can be found. 4.4. Textile Electrodes Textile sensors to be used for medical purposes are usually in contact with the skin. This is particularly the case for electrodes used for monitoring heart signals (cardiogram). In order to test the performance of textile structures for this application an actual cardiogram can be recorded; one of the main problems here is the extreme variability of the skin properties. Even for one person skin conductivity changes from moment to moment making objective testing very difficult. Therefore a phantom test set up has been developed [12]. In this method an electrolyte is used to simulate body fluids, separated from the textile electrodes by polymeric membranes mimicking the skin. (Fig. 11)
electrolyte solution
membranes
textile electrodes PVC tube
Figure 11. Impedance spectroscopy for characterizing textile electrodes.
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Signal transfer is analysed using impedance spectroscopy. This method allows to separate the impedance of the separate components of the system. By varying different parameters, their influence on resistivity can be studied quite easily in an accurate and reproducible way. Obviously, heart rate sensors are in permanent contact with the skin. This means that they will be wetted by sweat. Although stainless steel fibres resist corrosion due to for instance NaCl, at the skin a voltage also occurs, causing electrochemical attack. As a consequence the electric resistance increases in time when the material is in contact with artificial sweat (measured using the set up described above) [8] (Fig. 12).
450
R (ohm
400 knitted
350
woven 300
non woven
250 200 0
100
200
300
400
500
600
time (h)
Figure 12. Effect of corrosion of stainless steel fabrics on electrical conductivity.
This graph clearly demonstrates that corrosion has a significant impact on the conductivity of the sensor: the resistance nearly doubles in a couple of weeks time. This means that the accuracy of the sensor will be reduced significantly.
5. Conclusions Smart textile structures are here to stay. They have demonstrated their feasibility both from the point of view of technical specifications as well as regarding their textile character.
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The enormous versatility of textiles in terms of (combinations of) fibre types to be used, processing technologies and textile structure is at the same time an opportunity to be exploited but also a confusing space of possibilities. Different textile materials may show different, even opposite behaviour. It is a huge challenge to find the right set of materials for each particular application. Properties that are beneficial for one application may be disruptive for another one. Technical features may be in contrast to textile characteristics so a balance may have to be looked for. Objective testing is another field of research. No evaluation is possible without an accurate and reliable test method. But the result will be worthwhile, as it will definitely lead to a better quality of our lives.
References [1] P. Xue, X.M. Tao, K.W.M. Kwok et al., Electromechanical behaviour of fibres coated with an electrically conductive polymer, Textile Research Journal 74 (10): 929–936 (2004). [2] Yanagizawa H., Kodaira T., Dependence of electrical conductivities of carbon black filled nylon-12 fibers on spinning conditions Sen-I Gakkaishi 60 (7): 203–212 JUL (2004). [3] B.R. Mattes, Electronic textiles based on intrinsically conducting polymer fibre, New generation of wearable for e-health: towards a revolution of citizens’ health and lifestyle, December 11–14 Lucca, Italy (2003). [4] E. Devaux, D. Saiha, C. Campagne, C. Roux, B. Kim, M. Rochery, V. Koncar, Nanocomposite fibres for the processing of intelligent textile structures, 5th World textile conference AUTEX, (2005), 2–8. [5] L. Van Langenhove, C. Hertleer, Smart textiles for medical purposes, MEDTEX 03, International Conference and Exhibition on Healthcare and Medical Textiles, July 7–9th, Bolton UK (2003). [6] http://www.smartex.it/uk/projects/physensor.htm. [7] http://www.medes.fr/VTAMN.html. [8] www.gtwm.gatech.edu. [9] Priniotakis J., PhD thesis: Study of Conductive Textile Electrodes as Analytical Tool for Detection of Parameters related to human body by (EIS) Electrochemical Impedance Spectroscopy, Ghent University, to be published (2005). [10] X. Tao, Fibre based interactive textiles and nanotechnology, International Conference on Intelligent Textiles, Gent 25 June (2004).
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[11] Lanfer B., master thesis: The development and investigation of electroconductive textile strain sensors for use in smart clothing, Ghent University, June 2005. [12] P. Westbroek, G. Priniotakis, L. Van Langenhove and P. Kiekens; Method for quality control of textile electrodes used in intelligent textiles by means of (EIS) Electrochemical Impedance Spectroscopy, Accepted for publication in Textile Research Journal (2004).
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Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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Optical Chemical Sensors and Personal Protection Aleksandra LOBNIK University of Maribor
Abstract. Optical sensors offer a wide field of application and are of potential utility in all kinds of analytical sciences. Typical area is pollution and process control, biotechnology, protection and defense, seawater analysis, clinical chemistry and invasive biomedical techniques. The interdisciplinary nature of optical chemical sensors opens a variety of new directions in sensor development. The issue of chemical selectivity is still the most challenging. There are several ongoing directions for improving the selectivity of optical chemical sensors. One way is certainly in the field of supramolecular organic chemistry, and in the synthesis of the highly selective receptor molecules which will posses a chromogenic or fluorogenic part. Furthermore, biomonitoring can serve as a basis and the first step towards the development of "living sensors". It is already a well-established in the field of environmental analysis and there are big potentials in the area of protection (DNA chips). In addition, the development in sensor materials opens a number of new possibilities, such as incorporation of organic and biochemical specific sites into inorganic matrices and all this knowledge could be resumed in development of new optical sensors based on molecular imprinted polymers. The recent progress in miniaturized integrated optical sensors offer several advantages, such as a possibility of mass-producing, low-cost sensor chips. By placing multiple sensing regions (sensing pads) on a single chip, the multi-component sensing with on-chip referencing becomes possible.
Keywords. Optical chemical sensors, indicators, polymers, optical fiber chemical sensors, molecular imprinting, DNA chips, applications
1. Protection Of the major steps toward controlling this problem is to develop sensor devices that can act as an early warning system to the endangered personnel. Nerve agents are chemicals that attack the central nervous system. A release of a nerve agent has the potential to rapidly affect a large number of people. The majority of nerve agents belong to a class of compounds called organophosphates [1, 2]. The development of an early warning system, based on detection of toxic materials, is now an important topic for research and development. Fiber optic sensor systems provide with numerous advantages over conventional systems which include immunity to electromagnetic interference, small and compact size, sensitivity, ability to be multiplexed, remote sensing and to be embedded into textile structure [3]. An optical fiber forms an effective medium to sense chemical species. The presence of chemical species can modulate light property such as intensity, phase or polarization in the
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optical fiber. These changes can be detected at the fiber output and can be related to the concentration of the chemical species present at the point. Sensing of chemical agents using fiber optic sensor systems has been reported in literature for 50 – 60 years [4]. These include sensors for toxic chemicals such as ammonia, hydrazine, hydrogen peroxide, organophosphate nerve agents [5, 6]. Developments on the chip level sensors illustrates the potential for nanotechnology based approaches to detection of and protection from chemical, biological, radiological, and explosives threats [7].
2. Optical chemical sensors 2.1. Analytical aspects of sensors Research on chemical sensors represents an expanding branch of analytical chemistry. The importance and power of chemical sensors in analytical and clinical chemistry has been recognized for many years. Classical analytical procedures are usually performed by means of sophisticated instrumentation which cannot be easily moved away from laboratory, requiring thus the transport of the sample to the lab. In contrast to such methods, chemical sensors provide a possibility of real-time analysis, which can be accomplished directly in the field, plant, home, or in the hospital. Ideally, such a sensor can be stuck directly into the sample and the result of the measurement is displayed within a couple of seconds. The ultimate power of the ideal chemical sensor is the ability to provide the spatial and temporal distributions of a particular molecular or ionic species in real time. In general, the sensor requirements are defined by the specific application. Nevertheless, following features are of particular importance for all types of sensors, and thus, they must be carefully considered in R&D of sensors [8]: x sensitivity in the range of interest x selectivity for the analyte x broad dynamic range x reversibility x robustness and reliability x lack of frequent calibration x fast response x inertness to sample matrix x unattended operation x small size x low cost 2.1.1. Definition and classification of chemical sensors Several definitions of chemical sensors have been proposed in literature and the discussion about the characteristics and requirements of sensors is still going on. According to the definition given by IUPAC Commission on General Aspects of Analytical Chemistry, a chemical sensor is a device that transforms chemical information, ranging from the concentration of a specific sample component to total composition analysis, into an analytically useful signal. The chemical information may
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originate from a chemical reaction of the analyte or from a physical property of the system investigated [9, 10]. From a more application-oriented point of view a chemical sensor is defined as a small-sized device capable of continuously and reversibly reporting a chemical concentration or activity directly in the sample matrix. Typically, a chemical sensor consists of a chemical recognition phase coupled with a transduction element (Figure 1).
Figure 1. Schematic representation of the composition and function of a chemical sensor
Some sensors may include a separator which is, for example a membrane. In the receptor part of a sensor the chemical information is transformed into a form of energy which may be measured by the transducer. The transducer part is a device capable of transforming the energy carrying the chemical information about the sample into a useful analytical signal. The transducer does not show selectivity. The receptor part may be based on various principles (Figure 2): x physical, where no chemical reaction takes place. Typical examples are those based on measurement of absorbance, refractive index, conductivity, temperature or mass change. x chemical, in which a chemical reaction with participation of the analyte gives rise to the analytical signal x biochemical, in which a biochemical process is the source of the analytical signal. They may be regarded as a subgroup of the chemical ones. The most popular source of "selectivity" is biology. Sensors having a receptor part based on a biochemical principle are usually called biosensors. Selectivity and sensitivity provided by nature have been utilized in such sensors, frequently by immobilizing the biologically active compounds, such as enzymes and immunoglobulins, within a receptor part of the sensor. The effective way of obtaining the biological selectivity is the combination of cell cultures, tissue slices, organs and sometimes of whole living organisms with the transducer. Chemical sensors may be classified according to the operating principle of the transducer as optical, electrochemical, electrical, mass sensitive, etc. There are two large groups of sensors, namely electrochemical and optical ones. In addition, mass sensitive sensors such as piezoelectric and surface acoustic wave
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devices have demonstrated a great potential in immunosensing and for detection of gaseous species. A RECEPTOR PART
chemical
physical
bichemical (BIOSENSORS)
B TRANSDUCER
optical
electrochemical
absorptiometry voltammetric sensors reflectometry potentiometric sensors luminescence CHMFETs IR spectrometry Raman spectrometry light scattering optothermal effect fiber refractometry surface plasmon resonance
electrical
magnetic
thermometric
mass sensitive
Figure 2. Classification of chemical sensors according to the operating principle of the receptor and transducer
2.1.2. Optochemical sensors (OPT(R)ODES) Terms "optrode" (from optical electrode) and "optode" (from the Greek RSWLNRs RGRs "the optical way") are frequently used expressions for optical sensors. Both terms stress the fact that the signal is optical rather than electrical [11-14].
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Optical sensors rely on optical detection of a chemical species. Two basic operation principles are known for optically sensing chemical species: x intrinsic optical property of the analyte is utilized for its detection x indicator (or label) based sensing is used when the analyte has no intrinsic optical property. For example, pH is measured optically by immobilizing a pH indicator on a solid support and observing changes in the absorption or fluorescence of the indicator as the pH of the sample varies with time. Fiber-optical chemical sensors (FOCSs) represent a subclass of chemical sensors in which an optical fiber is used as part of the transduction element. A major breakthrough in optical sensors was achieved when conventional optical sensing techniques were coupled to fiber optics. The communication industry has provided inexpensive optical fibers that allow the transmission of optical signals over large distances. Optical fiber technology is used to transmit electromagnetic radiation to and from a sensing region that is in direct contact with the sample. The chemical changes that occur because of interactions between analyte and immobilized reagents are measured spectroscopically by analyzing the radiation that returns from the sensing region. Alternatively, a spectroscopically detectable intrinsic physical property of the analyte can be measured directly through the fiber optic arrangement without a specific chemical recognition phase. This approach is termed remote spectroscopy. 2.1.3. Advantages and disadvantages of optical sensing The major advantages of optical sensors include [15-17]: x Optodes do not require a reference cell as in potentiometry. x The ease of miniaturization. x Remote sensing achieved by use low-loss optical fibers; over distances up to about 1 km. x Because the primary signal is optical, it is not subject to interferences caused by static electricity, strong magnetic fields or surface potential. x Multiple analysis with a single control instrument at a central site. x Coupling of sensors for different analytes in a sensor bundle of small size allows simultaneous monitoring of various analytes. Besides a number of advantages over other sensor types, optical sensors exhibit a number of disadvantages: x Ambient light can interfere. x Limited long-term stability because of photobleaching or wash-out of the immobilized indicator. x Mass transfer of the analyte from the sample into indicator phase is necessary in order to obtain a steady-state signal. x Limited dynamic range. x Selectivity of indicators and the immobilization techniques are to be improved. 2.1.4. Fields of applications Optical sensors offer a wide field of application and are of potential utility in all kinds of analytical sciences. Typical areas are pollution, detection and protection,
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process control, biotechnology, defense, seawater analysis, clinical chemistry and invasive biomedical techniques [18-30].
3. Indicator Chemistry 3.1. Indicators Indicators (probes) are synthetic dyes that undergo color changes on interaction with chemical species. The purpose of using a so-called indicator chemistry (i.e., a dye in or on a polymer support) in optical sensing is to convert the concentration of a chemical analyte into a measurable optical signal. In other words, the indicator acts as a transducer for a chemical species that frequently cannot be determined directly by optical means. This has an important implication in that it is the concentration of the indicator species that is measured rather than that of the analyte itself [31-34]. 3.1.1. pH indicators These are mostly weak acids (less often, weak basis) whose color or fluorescence is different in the dissociated and the associated (protonated) form, respectively [31, 35]. An important parameter for characterization of a pH indicator is its pKa value (i.e., the pH at which the dye is present in the undissociated and dissociated form at 50% each). The pKa is the negative log of the binding constant (which in turn is the inverse of the stability constant Ks): pKa = -log ([Ind-] [H+])/[H – Ind]
Eq. (1)
where [H-Ind] represents the concentration of the undissociated indicator molecule while [Ind-] denotes the concentration of the anion (the dissociated form which, in case of phenolic dyes, is more intensely colored), and [H+] is the concetration of protons (i.e., the negative antilog of the pH). At the transition point of the titration curve, pH = pKa. A typical titration plot as obtained from pH-dependent fluorescence emission spectra is shown in Figure 3, from which it is obvious that pH indicators are most sensitive at pHs near pKa, their dynamic range covers a pH range at approximately pKa +/- 1.5 units and the shape of the curve is different for the dissolved and immobilized forms of the dye.
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fluorescence intensity
100 M2
M1
80
M3
60
M4
40
20
0 4
5
6
7
8
9
10
11
12
13
pH Figure 3. Titration plots of aminofluorescein (AF) in poly- tetramethoxysilane (TMOS) (M1), ormosil (M4) and covalently immobilized on 3-(trimethoxysilyl)propylisocyanate (3-ICPS) (M2) and (glycidyloxy-propyl)-trimethoxysilane (GOPS) (M3)
3.1.2. Metal chelators There are many types of dyes that form colored complexes (chelates) with metal ions and therefore may be employed as indicators in optical sensors. However, the color reaction must be sufficiently selective and the value of the stability constant of the complex formed should be such as to make the reaction reversible in order to make the device a sensor rather than a single-shot probe. This appears to be a problem with most sensors for heavy metals [31-33, 36]. Metal indicators are usually salts of polybasic acids, which change in color when the acidity of the solution is varied. It is therefore mandatory to buffer the pH of the sample solution when an indicator of this type is used. The theoretical basis of the use of metal indicators can be discussed in terms of the so-called conditional constant Ks. When a metal ion M reacts with an indicator in a molar ratio of 1:1,
Ks = [M – Ind] / ([M’][Ind’]
Eq. (2)
Where [Ind’] denotes the concentration of the indicator, which is not bound in the complex M-Ind, and [M’] the concentration of the metal ion that is not bound to the indicator as [M-Ind]. 3.1.3. Crown ether dyes (Chromoinophores) This class of indicators dyes has attracted particular attention with respect to sensing alkali ions. Chromoiophores incorporate two functions in one molecul, namely that of a
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crown ether (or a more complex binding site) capable of binding alkali or alkaline earth ions (or a more complex binding site) capable of binding alkali or alkaline earth ions (but also certain main group metal ions), and that of a chromophore that is designed to bring about specific color changes [37-41]. The chromophoric groups can bear one or more dissociable protons or can be nonionic. In the former, the ion exchange between the proton and appropriate metal cations causes the color to change, while in the latter the coordination of the metal ion to the chromophoric donor of the dye molecule induces a change of the charge transfer (CT) band of the dye. If complexation is associated with the release of a proton, the sensor obviously will have a pH-dependent response. 3.1.4. Quenchable fluorophors Both the fluorescence intensity and the decay time of certain fluorophores are reduced in the presence of so-called dynamic quenchers. The process of dynamic quenching is fully reversible (i.e., the dye is not consumed in a chemical reaction). Hence, quenchable fluorophores comprise an important class of indicators for reversible sensing [42, 43]. In the case of dynamic quenching, the interaction between quencher (analyte) and fluorophore is in the excited state only. The relation between luminescence intensity (I) and decay time (W) on one side, and analyte concentration on the other is described by the Stern-Volmer equation:
(I0/I – 1) = (W0/ W - 1) = Ksv [Q] = Kq . W0 . [Q]
Eq. (3)
where I0 and I are the luminescence intensities in the absence and presence, respectively, of the quencher Q present in concentration [Q], W0, and W are the luminescence decay times in the absence and presence, respectively, of quencher Q, Ksv is the overall (Stern-Volmer) quenching constant and Kq is the bimolecular quenching constant. At higher quencher concentrations, Stern-Volmer plots tend to deviate from linearity. Oxygen is known to be notorius quencher of luminiscence, and this is widely exploited for sensing purposes [43-50]. Interferences by ionic species can be eliminated by immobilizing the fluorophore in ion-impermeable materials such as silicone or polystyrene. Other dynamic quenchers of luminiscence include bromide and iodide, halothane (which quenches by virtue of the so-called heavy atom effect of bromine) and the transition metals (which quench due to the presence of unpaired spins). 3.2. Polymeric supports and coatings 3.2.1. General aspects Polymer chemistry (as a part of the broad field of material sciences) is an extremely important part of the optical technology. Both the light guide (including its cladding and coating) and the sensing chemistry of indicator-mediated sensors are made from organic or inorganic polymer. The polymers used in optrodes can have one or more of the following functions [51-57].
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1.
It acts as a rigid support onto which the dye (or receptive element) is immobilized 2. It may act as a solvent or cage for the material to be immobilized 3. It can provide selectivity for certain species by virtue of the permselectivity of most polymers 4. Polymeric covers are frequently used as protective covers for sensitive working chemistries 5. They can serve as optical isolation so to avoid ambient light to enter the optical system of the optrode. The choice of polymer is governed by the permeability of the polymer for the analyte, its stability and availability, its suitability for dye immobilization, its compatibility with other materials used in the fabrication of optrodes, and its compatibility with the sample to be investigated. 3.2.2. Hydrophobic polymers Silicones Silicones have unique properties in possessing a higher permeability for most gases than any other polymer, but being impermeable to ions including the proton. The selectivity of sensors for carbon dioxide, for example, results from the fact that interfering protons do not pass hydrophobic membranes and therefore cannot interact with a dissolvent pH indicator [58-60]. Silicones also have excellent optical and mechanical properties, and unique gas solubility. In case of oxygen it exceeds all other polymers. Many silicones are of the room-temperature vulcanizing (RTV) type, and the respective prepolymers may be dissolved in aprotic solvents such as toluene or chloroform. This greatly facilitates handling. The main applications of silicone materials is in sensors for oxygen and other uncharged quenchers such as sulfur dioxide and chlorine, and as gas-permeable covers in sensors for carbon dioxide or ammonia. Silicones cannot be easily plasticized by conventional plasticizers, but form copolymers which may be used instead. Blackened silicone is a most useful material for optically isolating gas sensors in order to make them insensitive to the optical properties of the sample. Other hydrophobic polymers Poly(vinil chloride) (PVC), poly(methyl methacrylate) (PMMA), polyethylene, poly(tetrafluoroethylene) (PTFE), polystyrene, and ethylcellulose comprise another group of hydrophobic materials that efficiently reject ionic species. Except for polystyrene, they are difficult to chemically modify so that their function is confined to that of a “solvent” for indicators, or as a gas-permeable cover [61, 62]. Polymers that have a high glass transition temperature (Tg) are brittle. They require plasticizers to make them flexible. Furthermore, the high density/rigidity of the polymer chains (without plasticizers) hinders diffusion of ions and gases in the polymer matrix. Therefore, plasticizer to polymer ratios of up to 2:1 are required. While PVC is soluble in tetrahydrofuran and cyclopentanone, polymers such as PMMA, PS and PVAc are also soluble in ethyl acetate, ethylmethyl ketone, dichloromethane, etc. Polymers with low glass transition do not require plasticizers. However, these compounds are often unpolar and, consequently, bad solvents for polar ligands, ionophores, dyes, and analytes.
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3.2.3. Hdrophobic/Hydrophilic polymers Silica Materials Glass is widely used for manufacturing optical fibres. Its surface may be made either hydrophilic or hydrophobic by treatment with a proper surface modification reagent. Surface derivatization is usually performed with reagents such as amino-propyltriethoxysilane which introduces free amino group onto the surface of glass to which dyes or proteins may be covalently attached. Glass does not measurably swell but is difficult to handle in view of its brittleness [63, 64]. Sol-gel form an attractive alternative to conventional glass [65]. 3.2.4. Hydrophilic polymer Hydrophilic polymers provide a matrix which corresponds to an aqueous environment. Hydrophilic supports are characterized by a large number of hydrogen-bridging functions such as hydroxyl, amino, or carboxamide groups, or by anionic groups (mainly carboxyl and sulfo) linked to the polymer backbone [65, 66]. Typical examples are the polysaccharides (cellulose), polyacrylates, polyacrylamides, polyimines, polyglycols, and variety of so called hydrogels. Depending on the degree of polymerization and cross-linking, they are water-soluble or water-insoluble. Ions can diffuse quite freely, but the possible water uptake (10-100%) can cause significant swelling of the polymer. Swelling of the matrix affects the optical properties of the sensors and, consequently, the signal changes. Throughout, they are easily penetrated by aqueous solutions and display poor compatibility with hydrophobic polymers such as silicone and polystyrene. Most hydrophilic polymer membranes are easily penetrated by both charged and uncharged low molecular-weight analytes, but not by large proteins, and have found widespread application as support for indicators. 3.3. Immobilization techniques 3.3.1. Hydrophobic interactions Most indicator chemistry is adapted to aqueous solution (for titration in water). Therefore, the molecules are water-soluble and if dissolved in lipophilic polymers, they are washed out immediately. In order to make dyes, ionophores and ligands soluble in polymers and to avoid leaching of the components, they have to be made lipophilic [67]. Lipophilic molecules can be obtained by introduction of long alkyl chains. However, the chemical synthesis involved can be tedious. Therefore, another possibility is to obtain lipophilic compounds by ion-pairing. Ion pairs are mostly obtained by dissolving both components (water-soluble ionic indicator and watersoluble ionic surfactant of opposite charge) separately in water, pouring both solutions together and filtrating the precipitated product. 3.3.2. Ion - exchange Indicators can be made lipophilic by ion-pairing with surfactants. However, they can also be directly immobilized on the polymer by ion-pairing with ionic polymers (polyelectrolytes) [68]. Solutions or suspensions of the polymers are usually mixed with aqueous or alcoholic solutions of the dyes.
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3.3.3. Covalent immobilization Covalent immobilisation of the indicator chemistry to the polymer matrix is preferred method. The operational stability and shelf life is superior (no leaching, crystallisation, evaporation of components) [69,70]. However, to obtain indicator chemistry and polymers with functional groups is inevitably linked with significant synthetic effort. Very often, chemical modification of dyes negatively affects their selective and sensitive analyte recognition. In principal two different ways of immobilisation are possible, namely (a) to bind a reactive dye (e.g. fluorescein succinimidyl ester) to a reactive polymer matrix (e.g. aminocellulose), or (b) to polymerize a reactive dye (e.g. a dye with a methacrylate group) with common monomers (e.g. methyl methacrylate) to give a copolymer. Several indicator dyes are available in a reactive form (primarily for labelling of peptides). These reactive molecules with isothiocyanate groups, sulfonyl chloride groups, vinylsulfonyl groups, or succinimidyl groups (fluorescein isothiocyanate, dabcyl succinimidyl ester, hydroxypyrene trisulfonyl chloride) can be covalently attached to aminoethylcellulose or amino-PVC. Indicator dyes with amino or hydrazino groups such as aminofluorescein, shown in Figure 4 can be coupled to isothiocyanate or epoxy groups of 3-(trimethoxysilyl)propylisocyanate (3-ICPS) and (glycidyloxy-propyl)-trimethoxysilane (GOPS). 3.3.4. Chemical doping Immobilization of organic modifiers in organic polymers during the polymerization or the molding process is a well-known method for the modification of polymers. Avnir, Levy, and Reisfeld at the Hebrew University of Jerusalem [71] were the first to realize that moderate or even ambient temperature sol-gel processing opens the way for immobilization of heat-sensitive compounds by incorporation of the modifiers in the sol-gel precursors. This so-called “sol-gel doping” method is gaining popularity as a result of its generality and simplicity. This concept is intermediate between impregnation and covalent bonding techniques and provides a general, inexpensive route for the immobilization of reagents. Its drawback is a certain degree of leaching of the organic modifier.
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COOH O=C=N-(CH2)3-Si (OMe)3
+
HO
O
O O HN
C
NH (CH2)3-SI (OMe)3
COOH
HO
O
O
NH2
COOH +O
HO
O
O=C=N-(CH2)3-Si (OMe)3
O HN
OH
O (CH2)3-SI (OMe)3
COOH
HO
O
O
Figure 4. Reaction scheme for covalent immobilization of aminofluorescein via 3(trimethoxysilyl)propylisocyanate (3-ICPS) and (glycidyloxy-propyl)-trimethoxysilane (GOPS) and co-polymerized with tetramethoxysilane (TMOS)
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4. Applications 4.1. Optical sensors for determination of blood gases, pH and ions The OPTI Critical Care Analyser (CCA) (Figure 5) is a fully automated in-vitro diagnostic Point-of-Care instrument that measures critical care parameters in blood, plasma and serum. The analyser utilises disposable sensor cartridges providing different analyte configurations. The cartridge is based on fluorescence sensors to measure blood gases and electrolytes and employs reflectance/absorbance technologies to measure hemoglobin [72].
CO2
Na+
O2 tHb/SO2
K+
pH
Ca++ or Cl Figure 5. AVL OPTI CCA: Instrument and cartridge
4.1.1. Sensor technology O2 Optode The indicator layer of the O2-sensor (Figure 6) contains a fluorescent O2-sensitive dye. For optical isolation, the indicator layer is coated with a black O2-permeable layer.
Indicator layer
O2
120 rel. flu. intensity S
Black overcoat
100 80 60 40 20 0
Dye
0
100
200
P O 2 [ Torr ]
blue light
red light
Figure 6. O2 -optode: Cross section and O2 -response
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pH Optode The indicator layer of the pH-sensor (Figure 7) contains cellulosic fibres, loaded with a pH-sensitive fluorescent indicator dye, embedded in an ion-permeable hydrogel. For optical isolation, the indicator layer is coated with a black ion-permeable hydrogel.
T ra n s p a re n t h y d ro g e l
B la c k h y d ro g e l o v e rc o a t
H
+
rel. flu. intensity S
120
D yed c e llu lo s ic fib e rs
100 80 60 40 20 0 6
g r e e n lig h t
b lu e lig h t
7
pH
8
9
Figure 7. pH Optode: Cross section and pH-response
CO2 Optode The CO2 sensor (Figure 8) differs from the pH sensor in that the indicator layer is coated with a black, CO2 permeable, ion-impermeable layer.
H+
T ra n s p a re n t h y d ro g e l w ith H C O 3 - b u ffe r
C O 2 + H 2 O = H C O 3 -+ H +
100 80 60 40 20 0
D yed c e llu lo s ic fib e r s
b lu e lig h t
120 rel. flu. intensity S
B la c k o v e rc o a t
CO2
0
40
80
120
P C O 2 [ T o rr ]
g r e e n lig h t
Figure 8. CO2 Optode: Cross section and CO2 -response
Na+, K+ and Ca++ Optodes Recently, we introduced a new family of patent-pending fluorescent indicator dyes (fluoroionophores, FI) for determination of blood Na+, K+, and Ca++ (Figure 9). The three FI’s share a common design. Essentially they consist of an ionophore part, able to reversibly bind the analyte ion with appropriate specificity at physiologic ion
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concentrations, a spacer part and a dye part. A linker group connected to the dye part is available for covalent attachment. The ionophore is able to trigger the fluorescence of the adjacent dye in dependence of the analyte concentration.
Figure 9. Fluoroionophores
4.2. Examples of absorption–based sensors The sol-gel co-immobilization of a non-fluorescent blue indicator bromothymolblue (BTB) with an europium (III)-complex intense antenna mediated lanthanide dye represents a new scheme for the fluorescence analysis [72]. Luminescence spectra of europium (III)-complex shown in Figure 10 were found to be independent of pH changes in the range 1-10. Therefore, BTB, a non-fluorescent pH indicator with alkaline absorption maximum close to main europium emission band was added to the sol-gel mixture to shield reversibly the emission of the europium (III)complex at different pH’s without quenching of the antenna function.
Figure 10. Europium (III) complex
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Figure 11 shows pH response of bromothymolblue (BTB) as co-immobilized non fluorescent pH indicator detect by fluorescence.
fluorescence intensity
125
pH=7.88
pH=6
100
pH=8.32
75 50
pH=9.98
25 0 500
400
600
700
wavelength /nm
Figure 11. pH response of bromothymolblue (BTB) as co-immobilized non-fluorescent indicator detect by fluorescence
An optical sensor highly sensitive to hydrogen peroxide has been prepared by incorporating the indicator dye Meldola Blue (MB) into sol-gel layers, prepared from (a) pure tetramethoxysilane (TMOS) and (b) variation of TMOS and methyltrimethoxysilane (Me-TriMOS) (Figure 12). Sensor layers based on TMOS doped with MB were found to be most appropriate for purposes of sensing hydrogen peroxide in giving large signal changes and displaying rapid response times over the wide concentration range of 10-8 – 10-1 M (Figure 13) [73].
2 ,5 1
Absorbance
2
1 ,5
1 2
0 ,5
0 420
490
560
630
700
770
w a v e le n g th / n m
Figure 12. Absorbance spectra of dissolved oxidized form of MB (1) and immobilized MB in poly-TMOS sensor layer L1 (2)
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Absorbanca
0,385
10
-1
-1
M
10 M
0,375 -8
10 M
-3
10 M Na2S2O3 0,365 200
700
1200
1700
2200
t/s
Figure 13. Response of sensor layer L1 to dissolved hydrogen peroxide at pH 7 and its reversibility by exposing to Na2S2O5 measured at 720 nm
The selective determination of Cu(II) was accomplished by making use of Pyrocatechol Violet indicator, dissolved in plasticized PVC membrane as a lipophilic ion pair with tetraoctylammonium cation. The membrane response to Cu(II) by changing colour irreversibly from yellow to green (740 nm) [74]. The chemical structure of Pyrocatechol Violet and the Pyrocatechol Violettetraoctylammonium ion pair are shown in Figure 14.
Figure 14. Chemical structure of Pyrocatechol Violet (1) and the Pyrocatechol Violet–tetraoctylammonium ion pair (2)
The dynamic response to Cu(II) was monitored as a change in absorbance at 740 nm as the membrane was exposed to a buffer solution containing copper ions. Characteristic response curves obtained for different concentrations of Cu(II) are shown in Figure 15.
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Figure 15.Typical dynamic response curves of membrane recorded at 740 nm as a result of exposure to different concentrations of Cu(II)
5. DNA chip technology-design of the sensor surface
Introduction Biochips are bioanalytical devices applicable to diagnostics, drug discovery, and life science research. Diagnostics include a range of targets including metabolites, proteins, microbes, toxins, and drugs for medical, veterinary, environmental, and agricultural applications. New modes of drug discovery, applicable to biochips, encompass target identification, lead compound discovery and optimization, and toxicology. Life science research connects to biochips in the areas of gene discovery and functional genomics. Biochip technologies have broad potential, but are especially useful in the areas genomics, high-throughput screening, and infectious disease diagnostics. Biochips incorporate elements of microfluidics, micromaching, synthetic chemistry, separation science, and detection technologies. Key attributes include [75-81]: x Miniaturization x Functional integration x Parallelism x Virtual automation Biochip companies divide roughly into two camps: those focused on micro-arrays and those focused on the functionally integrated lab-on-the-chip. Arrays are mainly used for gene expression, genotyping, and hybridization assays, while the lab-on-a-chip serves primarily for chemical separations, ligand receptor assays, and cell-based assays. 5.1. Applications and product development The biochip world, for purposes of this discussion, is divided into three areas: genomics, diagnostics and research. 5.1.1. Genomics Genomics is an exciting new discipline in modern biology focusing on genome mapping, sequencing and analysis. Such studies promise to advance our understanding of genetic variation and its consequences on biological function [80-85]. Genomics
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derive largely from the Human Genome Project, an international undertaking to characterize the entire human genome. Functional genomics studies center on polymorphisms (determining the range of sequence variations among individuals and the significance of these variations) and gene expression studies (the circumstances under which genes express or fail to express in both normal and diseased individuals) which provide a wealth of new targets for pharmaceutical and biotechnology application. In order to deliver genetic information quickly, cheaply and accurately without the need of large quantities of samples high throughput, automation and miniaturization of the processes is required. Chip-based microsystems accelerate the functional genomics process simply because it is much faster to view many things at once than it is to view one or a few things. With biochip arrays it is now possible to view the expression of many or all genes in a particular tissue simultaneously. It is also possible to perform differential analysis of all genes in healthy tissues versus diseased tissue in a single experiment. Additionally, scientists can follow gene expression over time or before and after a drug is administered. Once differential patterns are known, one can test drug candidates for their effect on gene expression. 5.1.2. Diagnostics While it is highly likely that biochip arrays will play a key role in research activities directed at establishing the role of genetic markers in various disease states, it is unlikely that high volume diagnostic opportunities based on genotyping will go commercial in the short-term [86]. The medical utility of genotyping tests has not yet been fully established or characterized, and social issues based on privacy remain a barrier. Infectious disease diagnosis using biochips and low density oligonucleotide arrays promises to have broader implications for diagnostics in the short term than genotyping or genetic disease screening. Infectious agent tests can make good use of biochip capacities for parallel assays in screening for multiple organisms simultaneously. Another scenario for arrays involves screening specimens for one or several organisms together with their drug resistance genes. Classical culture-based methods for measuring antibiotic susceptibility take days to produce results. Genebased tests can reduce times to an hour or less. The medical and protection benefits of such acceleration are highly significant. 5.1.3. Life Sciences Research Biochips do two things particularly well: they permit massive parallelism and they make some processes go faster (e.g. electrophoresis, chromatography, PCR thermocycling). One class of biochip research opportunities involves simply accelerating classical processis. More exciting, and more speculative, possibilities relate to the use of biochips in new research paradigms [87, 88]. Arrays for genotyping HIV genes involved in drug resistance, illustrate the technology’s potential. HIV exhibits a high degree of polymorphism through frequent genetic shifts. Variability is so high that virial nucleic acids isolated from different patients are unlikely to have the same sequence. This extensive polymorphism increases the incidence of drug-resistant viruses leading to AIDS recurrences in patients under treatment. As the number of AIDS drugs increases, it becomes increasingly important to track mutations in individual patients through genotyping. The hope and expectation of this field, called pharmacogenomics, is that treatment can be
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individualized to the patient. Similar logic applies to genotyping of oncogenes. The p53 gene, with ist hundreds of mutations relating to human cancers, is a very active target of investigation. The hope is to specify prognosis and therapeutic intervention based on a simple genotyping assay. Perhaps the most exciting short-term opportunities for arrays in genotyping relate to BRCA1, a gene implicated in breast cancer. The most promising non-genomic research applications of biochips are in high-throughput screening (HTS) (many assays done in parallel) for drug discovery. Several kinds of assays are involved including ligand-receptor assays, celkl-based assays, and enzyme inhibition assays. Ligand-receptor assays utilize drugs as ligands which bind to natural receptors or quasi-receptor antibodies. Interactions in this category demonstrate binding, but say little about effects of ligands on cell function. To test function, it is best to use cells. When drugs bind to receptors in situ, they can affect cell function and assays can sometimes be devised to monitor these effects.
6. Molecularly imprinted polymers
Introduction During the last few years molecular imprinting became an emerging technique for producing synthetic materials with molecular recognition properties. Molecular imprinting technology (MIT) can be performed in several ways and leads to highly stable synthetic polymers with possessing binding specificity for a desired molecule [89, 90]. Molecular recognition between a molecular receptor (host) and a substrate (guest) happens if the binding sites of the host and guest molecules complement each other in size, shape and chemical functionality. In order to prepare molecularly imprinted polymers (MIPs) the requested guest substances are used as templates during the polymerization process, where they serve as a structure-directing compound within the growing polymer network creating cavities inside a highly cross-linked matrix. Due to the high degree of cross-linking the cavities maintain their shape after extraction of the template and thus, the functional groups are kept in an optimal configuration for rebinding the template. 6.1. Concept of molecular imprinting Basically molecular imprinting involves three main steps of preparation [91]: x The desired template molecule interacts with complementary functional monomers in a suitable solvent, either covalently or non-covalently. x A cross-linker “freezes” the template-monomer complex and incorporates it into a polymeric network. x After completed polymerization the template is extracted and cavities complementary to the template molecule are revealed. Following this basic procedure, several strategies have been developed involving organic polymers in general and free radical polymerization in particular. Two different approaches can be perceived currently:
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x the pre-organized or covalent approach, where covalent interactions between the template and the functional groups in the polymer are responsible for template specificity x the self-assembly or non-covalent approach, where exclusively non-covalent and metal-coordination interactions are involved 6.1.1. Selected applications of molecularly imprinted polymers During the last few years a novel approach called molecular imprinting chromatography has been developed and several intriguing separations, which have exhibited high separation factors and resolutions, have already been performed. Following the principles of affinity chromatography, separation and purification is achieved by using the interactions between a stationary molecularly imprinted polymer and a mobile liquid phase [92, 93]. Hence, there is a significant potential for the application of MIC in molecular separation and isolation. Within this field of approaches especially chiral separations have been a major area of investigation and molecularly imprinted materials have been extensively employed as chiral stationary phases in HPLC. A particular characteristic feature of these stationary phases is the pre-determined elution order of the enatiomers, which only depends on which enantiomeric form was used as the print molecule. In conclusion the MIC technique is likely to provide a useful tool to estimate the potential of imprinting effects of these synthetic polymers. 6.1.2. Chemical sensors The ability to produce chemical sensors with the high selectivity typical for biological and biochemical recognition using enzymes, antibodies or special imprint molecules, while obtaining the robustness to operate in a harsh environment, is a long-term aim of sensor research. Especially the stability of biological compounds in sensor systems is limited to a restricted period of time and they have to be exchanged to guarantee constant performance. Recently, MIPs have been applied in chemical sensors as substitutes for biological receptors (biomimetic sensors) and furthermore there is a great potential for the detection of molecules where a suitable biological component is not available. Several MIPs have already been investigated in respect to their potential application as recognition element in chemical sensors [94-96].
7. Optical fiber gas sensors
Introduction Fiber optic sensors are class of sensors that use optical fibers to detect chemical contaminants. Light is generated by a light source and is sent through an optical fiber. The light then returns through the optical fiber and is captured by a photo detector. Some optical fiber sensors use a single optical fiber while others use separate optical fibers for the light source and for the detector. There are three general classes of fiber optic sensors. The first type is completely passive. A spectroscopic method can be used
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to detect individual types of contaminants. This method involves sending a light source directly through the optical fiber and analyzing the light that is reflected or emitted by the contaminant. The refractive index of the material at the tip of the optical fiber can be used to determine what passes (vapor, water, NAPL) are present. A second class of fiber optic sensors consist of a fiber optic sensor with a chemically interacting thin film attached to the tip. This film is formulated to bind with certain types of chemicals. Contaminant concentration can be found by measuring the color of the thin film, the change in refracting index, or by measuring the fluorescing of the film. The third type of fiber optic sensors involves injecting a reagent near the sensor. This reagent reacts either chemically or biologically with the contaminant. The reaction products are detected to give an estimate of the contaminant concentration [97,98].
7.1. Optical-Fibre-Based Gas Sensor Systems The first workers to demonstrate, experimentally, the practicality of the technique were from the group at Tohoku University [99]. The first gas chosen for the implementation of their method was Nitrogen dioxide, an impurity in vehicle exhaust gases, which has a useful electronic absorption line in the visible region, at 496.5 nm. The method involved a single channel fibre-remoted spectrometer with two-wavelength referencing, one wavelength on the absorption line, the other displaced from the line of interest. The first practical demonstration of methane gas detection over optical fibre paths [100] was performed by workers from the Norwegian Institute of Technology, Trondheim. Their laboratory system used a broadband white light source and a rotating-chopper/interference-filter arrangement to sequentially interrogate the transmission of the sample cell, over the desired fibre optic cable link. This transmission was compared with that over a more-direct, free-space reference path. The first fibre-remoted methane detection scheme to be truly field tested was reported by Stueflotten et al [101], of A/S Elektrik Bureau, Norway. This system had much in common with the one just described, i.e. it used a compact chopped-LED source and synchronous detection. However, now steps were taken to enhance the long term stability of the system by using a dual-LED system, with one LED source centred on the absorption band and the other centered in an adjacent (non-absorbing) region of the spectrum. These sources were alternately pulsed and the outputs combined into the transmit fibre, using a passive coupler. On their return to the detector, after passage through a two-pass cell and a return fibre, the pulsed signal amplitudes in each band were electronically compared with a more directly derived sample of the transmitted light signals from each LED. The other system referred to above was a hydrogen gas sensor [102]. This is based on the dimensional expansion experienced by Palladium metal when it adsorbs hydrogen gas. This occurs by a well-known process, in which the gas is occluded at interstitial sites of the atomic lattice of the Palladium. The metal, in the form of a thin wire, was bonded to one fibre arm of a Michelson interferometer. The resulting linear dimensional change in the Palladium, which is proportional to the square root of the hydrogen partial pressure, was transferred to the fibre and detected by a highly sensitive interferometric method. All the above papers have relied on absorption processes. In the introduction, the basis of Raman scattering was described. This spectroscopic tool, which has potential
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for general chemical analysis, has only recently been applied to optical fibre gas sensing. The advantage of the method is its capability to explore energy levels in the mid- and far- infrared, yet use visible light for both the excitation and scattered beams. In addition, gases such as Nitrogen, without significant IR absorption bands, can still be measured. This is due to the different selection rules associated with Raman transitions. However, Raman scattered light, even from solid samples is extremely weak. For gases, it is even weaker and it was found necessary to use a photomultiplier, in photon counting mode, and average for tens of seconds, in order to detect the weak Raman light from a relatively concentrated gas sample [103]. Of perhaps more practical promise are the methods using polymer-clad silica fibres, in which the polymer is impregnated with a gas-sensitive dye. Such methods offer the possibility of sensing a wide variety of different gaseous species, depending on the selection of a suitable gas/dye reaction. The method also offers potential for distributed sensing using optical time domain reflectometry (OTDR) techniques. The two main doped-polymer-cladding methods reported so far are: a) The use of a fluorescent dye in the cladding, which has its fluorescence quenched by oxygen gas, [104] b) The use of a fibre cladding containing an indicator dye, sensitive to pH changes, such changes arising from interaction with ammonia gas, [105]. (Acid gases would interact in a converse manner). The latter method, as yet, appears to have problems in achieving the necessary reversibility. Unfortunately, with evanescent field sensors, there are likely to be practical problems with the temperature dependence of the cladding refractive index (which affects both the fibre numerical aperture and the evanescent field depth). In addition, there is also likely to be a dependence of both the fibre N.A. and the chemical-indicator reaction rate on the relative humidity of the environment to be sensed (Many chemical reactions halt, or proceed at a very slow rate under dry conditions). Finally, the evanescent field intensity will generally be a function of the spatial configuration of the fibre. Any bends in the fibre will affect the modal power distribution at the measurement point, by causing mode conversion, and conversion of power to higher order modes will result in a much stronger evanescent field, and hence greater apparent absorption.
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Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
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Ergonomics of Protective Clothing; Heat Strain and Fit Hein A.M. DAANEN1, Peter A. REFFELTRATH, Claudy L. KOERHUIS TNO Defense, Security & Safety, The Netherlands
Abstract. Protective clothing enables humans to operate in adverse environments. However, protective clothing limits heat transfer and hampers task performance due to the increased weight. A good balance has to be achieved between protection on the one hand and human factors aspects on the other hand. In general, the focus is on the protection and consequently human factors aspects are underestimated. Improving ventilation through and under the protective clothing increases sweat efficiency and thus reduces heat strain. Ideally, the sizing of the protective clothing should reflect the human body dimensions. A relatively loose fit enables a wider movement range and better ventilation. In summary, in the selection and evaluation of protective clothing attention should be given to heat strain and fit issues next to the actual protection it offers.
Keywords. Protective clothing, heat strain, fit, sizing
Introduction Humans face the challenge to live and function even in extreme environments like cold or hot climates, high altitude, in areas with poisonous gasses, in space or under water. Even though humans are equipped with a wide range of physiological mechanisms to adapt to these adverse climates, some form of additional protection in the form of clothing and equipment is necessary. Over the years, the protective equipment has in some cases evaluated to a second skin; an indispensable extension of the human body. However, protective clothing also forms an extra strain for the human body due to its weight and due to the hampered heat transfer to the environment. This article summarizes some of the 1
Head of the Department of Human Performance, TNO Defence, Security & Safety, Business Unit Human Factors, PO Box 23, 3769 ZG, Soesterberg, The Netherlands. Tel. +31 346 356 402; fax +31 346 353 977; e-mail:
[email protected].
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human factors aspects of protective clothing and aims to make developers of protective clothing aware of the importance of this issue. 1.
Physiological and Psychological Load in Protective Clothing
Recently, Daanen et al. [2] performed a study to determine mood, mental task performance and physiological strain during walking in a hot environment with and without protective clothing. 1.1. Methods Eight male healthy subjects (age 21 r 3 years, stature 185 r 3 cm, weight 74 r 10 kg) participated in the study. The subjects signed an informed consent after the study was explained to the subjects. The Ethics Committee approved the experiment. 1. 2. 3. 4.
The subjects were dressed in shorts, T-shirts, socks, sneakers and a cotton combat suit, a combat suit with ballistic vest (including a ceramic plate at the chest), a combat suit with NBC protection in ‘ready’ position (without protective mask), a combat suit with NBC protection in ‘protection’ position (with AVON FM12 protective mask and rubber gloves during walking).
The combat suit weighed 1480 g. The ballistic vest, NBC ready and NBC protection added 6432, 2825 and 3813 g respectively. The combat suit was made from cotton. The NBC-suit was made of cotton with a Saratoga lining on the inside. In the NBC protection condition, subjects were wearing rubber gloves during treadmill walking only. The clothing ensembles were supplied to the subjects in balanced order. Each soldier participated five times in the study: one trial session to get accustomed to the test and four experimental sessions. One of the four clothing ensembles was used in each experimental session. During the trial session, only the combat suit was worn. The time period between the experimental sessions varied from one day to one week. Prior to the 200-minute exposure in the climatic chamber, the subjects performed a variety of tasks like shooting training for the duration of an hour for other purposes. During the experimental sessions, the temperature was set at 30°C and relative humidity at 50%. Before entering the climatic chamber, the subjects were instrumented with a heart rate watch and belt around the chest, rectal probe, and skin temperature sensors, which measured heart rate (HR), rectal temperature (Tr) and mean skin temperature (Tsk) continuously during the climatic chamber test. Mean body temperature (Tbody) was calculated as the weighed average of rectal temperature and mean skin temperature using a factor of 0.8 for the core and 0.2 for the skin. Three subjects entered the chamber consecutively and performed the following tasks:
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-
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Psychological test: Two psychological tests were used: The Multi Attribute Task Battery (MAT) and the Profile of Mood scale (POMS). The MAT consists of four tasks, which include a system monitoring task, a tracking task, a communication task and a resource management task. Subjects have to perform these four tasks simultaneously. Monitoring task performance measures include number of false reactions, number of omissions and mean reaction time. Tracking performance has been defined as the root mean square tracking error. Communication measures include number of inadequate responses (including channel and frequency errors, omissions, responses to other call signs and enter omissions) as well as response times. Resource management performance measures include the mean absolute deviation of fuel level in tanks. Due to a simultaneous performance of these four tasks, complex task performance can be measured. The Profile of Mood State (POMS) test consisted of five scales; anger (7 items), tension (6 items), depression (8 items), vigor (5 items), fatigue (6 items). Walking test. The walking test consisted of walking on a treadmill (Jaeger) for 20 minutes with a velocity of 7 km/hour. Thermal comfort was rated according to ISO 10551 (-4 = very cold, 0 = neutral, 4 = very hot) [6]. Dexterity tests.
The subjects were exposed to ten 20-minute time cycles. The cycles were as follows: 1. psychological tests (Multi-Attribute Task (MAT) battery, Profile of Mood States (POMS)) 2. walking on a treadmill (7 km/hour) with a 19.7 kg backpack 3. dexterity tests (Purdue test, Minnesota rate of manipulation test, directly after 10 minutes arm cranking a moment of 51Nm 4. psychological tests 5. walking on a treadmill 6. eating period 7. psychological tests 8. walking on a treadmill 9. dexterity tests 10. psychological tests Heart rate, thermal comfort and temperature were taken after 10 and 15 minutes of exercise during every time cycle. Mean heart rate was defined as the average heart rates after 10 and 15 minutes of exercise. This set-up enabled the analysis of clothing condition, time cycle and interaction effects. The analysis of clothing conditions, time cycle and interaction effects were determined using repeated measures analysis of variance (ANOVA). The Turkey Wholly Significant Difference (WSD) procedure was used to determine significant effects. For all statistical contrasts a 5% two-sided level of significance was used.
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1.2. Results
1.2.1. Heart rate
Heart rate ( bpm)
180 170
Heart rate after 10 minutes
160
Heart rate after 15 minutes
150 140 130 120 110 Time cycle 2 1 3 Combat suit
Time cycle 2 Time cycle 2 1 3 1 3 Protective vest NBC ready
Time cycle 2 1 3 NBC protection
Figure 1. Heart rate after 10 and 15 minutes of the time cycle wearing different clothing systems.
Heart rate measurements are shown in Fig. 1. An effect of clothing condition on heart rate was found (p<0.001). The highest heart rate was found wearing the NBC-protection outfit. Heart rate was similar for NBC-ready and the ballistic vest. The lowest heart rate was observed wearing the combat suit. The increase in heart rate during the time cycles (p<0.001) can be interpreted as a cumulative effect since the work load did not differ. Furthermore, a higher heart rate was found after 15 minutes of exercise compared with the heart rate after 10 minutes (p<0.001). No interaction effects between clothing condition time cycle and/or measurements at 10 and 15 minutes were observed.
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1.2.2. Temperature Body, skin and rectal temperature differed between clothing conditions (p=0.004, p<0.001 and p<0.001 respectively). For all temperature measurements, the highest temperatures were observed wearing NBC-protection, followed by respectively NBC-ready, ballistic vest and combat suit. Fig. 2 shows the results for body temperature. Higher values of body, skin and rectal temperatures were measured after 15 minutes of exercise compared with measurements after 10 minutes (p<0.001 for all temperature measurements). No interaction effect was found between clothing condition and the temperature measurements after 10 and 15 minutes. 37.8
37.4
o
Body temperature ( C)
37.6
37.2
Body temperature after 10 minutes
Body temperature after 15 minutes
37.0 36.8 36.6 36.4 36.2 Time cycle 2 1 3 Combat suit
Time cycle 2 1 3 Protective vest
Time cycle 2 1 3 NBC ready
Time cycle 2 1 3 NBC protection
Figure 2. Body temperature during walking
1.2.3. Thermal comfort Clothing had a significant effect on thermal comfort (p<0.001). The highest value for thermal comfort (implying worst thermal comfort) was observed wearing NBC-protection (Fig. 3). Wearing NBC-ready or the ballistic vest resulted in the same assessment of thermal comfort. Wearing the combat suit resulted in the lowest value for thermal comfort (implying the best thermal comfort). Significant differences were observed between thermal comfort after 10 and 15 minutes, with higher values for thermal comfort after 15 minutes (p<0.001). No difference in thermal comfort was found during the time cycles.
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Also, no interaction effects were observed between clothing condition, time cycle and measurements after 10 and 15 minutes.
Thermal comfort score
very hot (4)
hot (3)
warm (2)
slightly warm (1)
Thermal comfort after 10 minutes Thermal comfort after 15 minutes
neutral (0) Time cycle 2 Time cycle 2 Time cycle 2 Time cycle 2 1 3 1 3 1 3 1 3 Combat suit Protective vest NBC ready NBC protection
Figure 3. Thermal comfort after 10 and 15 minutes of exercise in the climatic chamber.
1.2.4. Mood state Clothing conditions had significant effects on all Profile of Mood items, with exception of anger. Tension was significantly higher wearing NBC-protection compared with the other clothing conditions (p=0.004). The highest values for depression and fatigue were also observed wearing NBC-protection (Fig. 4). However, the difference in depression score was only significant with the ballistic vest (p=0.03) and the difference in fatigue score was only significant with the combat suit and the NBC-ready outfit (p=0.003). The highest score for vigor was observed wearing a combat suit, which was significantly different with the NBC-ready outfit (p=0.04). A significant increase in fatigue was observed during the time cycles (p<0.001). Further, a tendency in time cycle effect was found for tension, which decreased during the time cycles. A significant interaction effect between clothing condition and time cycle was only observed for tension (p<0.001). This interaction effect was the result of a decrease in tension over the time cycles during the NBC-protection, while tension remained the same during the other clothing conditions.
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Anger
20
Tension 18
Depression Vigor
16 POMS score
Fatigue 14 12 10 8 6 4 Time cycle2 4 1 3 Combat suit
Time cycle2 4 1 3 Protective vest
Time cycle2 4 1 3 NBC ready
Time cycle2 4 1 3 NBC protection
Figure 4. Profile of Mood State scores
1.3. Discussion To assess the balance between protection and function, four different clothing ensembles (combat suit (CS), CS + ballistic vest, CS + NBC ready, CS + NBC protection) were evaluated during walking on a treadmill. This study showed considerable increase in physiological load due to wearing protective clothing relative to the performance in the CS, which was used as a reference. We are interested to trace back the basic parameters that cause this effect. We consider three main parameters: 1) clothing weight, 2) increased heat stress due to impaired heat loss caused by a larger area of the body that is covered by clothing or an additional clothing layer, and 3) wearing a protective mask. The relative contributions to increase in physiological and psychological strain were assessed as follows: Strain = RW x W + RHS x H + R -
In which: relative weight (RW) is a value between 0 (CS weight) and 1 (weight of CS + vest), the relative heat stress (RHS) is a value between 0 (CS heat strain) and 1 (heat strain in NBC-protection garments), W is the generic effect of clothing weight on physiological strain, H is the generic effect of heat stress on physiological strain, R is the generic effect of wearing a respirator.
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The RW values are 0, 1, 0.45 and 0.6 for combat suit, vest, NBC-ready and NBCprotection respectively. The RHS values are 0, 0.3, 0.8 and 1.0 consecutively. Three formulae remain with three unknowns (W, H and R) that we can solve mathematically by substitution. The resulting W, H and R values are 7.0, 7.7 and 5.2 for heart rate during walking. This means that the heart rate increase was about equally affected by clothing weight, reduced heat transfer and a bit less by wearing a respirator. The contribution of the respirator does not include the performance decrement due to reduced heat transfer or weight, but includes the additional performance decrement due to other aspects, like negative emotions. The values for W, H and R were 0.0, 1.0 and 0.4 for body temperature during walking. This means that clothing weight did not affect body temperature, but heat transfer reduction did. Fig. 2 shows that additional protective equipment increased body temperature (H=1.0). NBC clothing showed the highest increase in skin, rectal and body temperature. McLellan [8] and Malapane and Shaba [7] also found an increase in rectal temperature during a test wearing NBC clothing compared with a test wearing ordinary battle dress. The increased skin, rectal and body temperature in our study can be explained by the reduced ability to evaporate sweat while encapsulated in NBC clothing. Due to the reduced ability to evaporate sweat, heat transfer is decreased. As a consequence heat production is higher than heat loss. Reactions to the higher heat production are vasodilatation of the peripheral blood vessels and an increase in heart rate to provide the central part of the body with enough blood. Although the weight of the combat suit with ballistic vest was higher than the NBC ready condition, heart rate was not significantly different. The thermal stress of NBC-ready had the same effects on heart rate as the extra weight of the ballistic vest (W=7.0, H=7.7). Because most studies use either NBC-ready or NBC-protection systems, it was hardly investigated to what extend the respirator and the suit contributed to the thermal, physiological and psychological load. Boer and VandeLinde [1] for example found that task performance in NBC protection with respirator deteriorated considerably compared to combat suit only. However, it was unclear if the respirator or clothing were responsible. In our study all subjects wore both the NBC-ready and NBC-protection outfit. The difference between NBC ready and NBC protection yields information on the impact of the protective respirator only on physiological and psychological strain. Our analysis shows that wearing a respiratory mask adds to the physiological load (R=5.2 for heart rate), even if weight and extra body coverage are taken into account. We think that psychological aspects may play a major role, which is confirmed by the results of the subjective rating scale items (POMS): tension, depression and fatigue. It can be concluded that psychological and physiological strain increased when wearing additional protective equipment. A ballistic vest decreased performance mainly through its weight; chemical protective clothing decreased the heat loss leading to
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performance degradation. A protective mask negatively affects the mood of the wearer. The magnitude of the effects depended on the task, task duration and clothing system.
2. Cooling under protective garments In order to reduce the heat strain during work in protective clothing, several methods can be employed. First, cool drinks cool the body core and increase the thermal buffer for heat storage. Second, precooling before starting work in the heat may be effective using the same rationale [3]. Third, the permeability of the protective clothing may be improved, leading to enhanced sweat evaporation and thus better cooling. Finally, cooling systems may be constructed between the human skin and the protective clothing. The most simple system is to pump ambient air in the air gap between skin and clothing. This can be done with minimal effort and great efficiency. Reffeltrath et al. [9] performed an experiment that describes the effects of such a method for helicopter pilots.
2.1. Methods Five male and one female subjects participated in the study (age 23 r 4 years, stature 185 r 8 cm, weight 81 r 8 kg). All subjects were fully informed about the nature of the study and signed an informed consent. The helicopter pilots were instrumented and seated in an experimental set-up by which data on rectal temperature, skin temperature, sweat loss, heart rate, oxygen consumption, flight and cognitive performance data were collected. All six subjects flew the simulator in three different conditions; one neutral condition (15ºC Air temperature, 29ºC black globe temperature, 50% Relative Humidity), and two warm conditions (35ºC Air temperature, 49ºC black globe temperature, 50% Rh). One of the warm conditions included the use of the air-cooling vest; the other was without cooling. Ambient air was blown over the torso and upper legs in the vest, thus enhancing evaporation. During all conditions sunlight was simulated with two artificial suns. The helm was also ventilated (Gentex HGU-65P). The air-vest consists of air-channels with an air-impermeable layer on the outside and an air-permeable layer on the inside. An air- permeable area was constructed between the canals. The air-canals are stitched in and are kept open by plastic helixes. A blower supplies the vest and the helmet with an air-flow of 6.5 litre per second. This air enters two airbags at the bottom of the vest, one at the front and one at the back. These airbags are connected to the air-canals that run straight up to the top of the vest and down to the bottom where they are closed. The air flows through the canals and exits evenly over the whole length of the canals through the permeable inner layer of the vest. The circulating air will take up the produced sweat and thus cool the skin. The moist air escapes trough permeable
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parts between the coils and trough the arm- and neck-holes of the vest. A small pump (12 Volt, 35 Watt) aids in removing the moist air from under the survival suit. Subjects and their clothing were weighted separately before and after the experiment. Sweat evaporation was calculated by subtraction of the weight gain of the clothing from the subjects weight loss. Sweat efficiency was defined as the amount of evaporated sweat by the amount fluid loss. Skin temperature was measured by thermistors placed on the chest, back, upper arm and upper leg. Rectal temperature was measured with a sensor that was placed by the subject. Mean body temperature was calculated from the rectal temperature (90%) and the mean skin temperature (10%). Thermal comfort and thermal sensation was assessed according to ISO 10551 [6]. Subjects were asked to rate their comfort and temperature sensation at 15, 35, 55, 75, 95 and 115 minutes after the start of the experiment. The pilots had to fly through a box. Flight performance was quantified by the amount of time that the box was missed. During the flight, the subjects had to perform a cognitive memory task (CMT) for several minutes. 2.2. Results One subject stopped after 115 minutes during the 35ºC condition without cooling. During the same condition, another subject was taken out of the experiment after 99 minutes for his rectal temperature reached the exclusion criterion of 39ºC. Flight performance during the CMT task was worse during the hot conditions as compared to 15°C (Table 1). Also fluid loss was much more in the heat. In the warm condition without vest, only 367 g of the 645 g of produced sweat (57%) was evaporated. The remainder was taken up by the clothing (Table 1). With air cooling, the percentage evaporated sweat was 91%. Sweat evaporation and cooling power were significantly (p<0.01) enhanced in the warm condition with cooling compared to the neutral condition and the warm condition without cooling. A significant (p<0.01) difference in sweat efficiency was found between the two warm conditions and between the neutral condition and the warm condition without cooling. The flight performance during the CMT task was better with blower than without.
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Table 1. Results of the Experiment 15ºC no blower Mean SD Weight loss subject (gram) Weight gain clothing (gram) Evaporated sweat (gram) Average cooling power (Watt) Sweat efficiency
35ºC no blower Mean SD
35ºC with blower Mean SD
184
85
645
188
585
91
-29
35
279
147
56
38
213
83
367
57
529
72
144
56
248
39
358
49
1.19
0.22
0.59
0.09
0.91
0.06
Figure 5 shows the increase in mean body temperature since the start of the experiment for eight time points. Starting 45 minutes after the beginning of the experiment, a significant (p<0.01) difference in mean body temperature increase can be observed between all three conditions. The condition at 15ºC shows a small decrease in body temperature while the subjects flying at 35ºC have increasing body temperatures. With forced ventilation the increase in body temperature is less than without cooling. Increase in Mean Body Temperature (ºC)
1.4
**
A: 15ºC, no blower
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Figure 5. Increase in mean body temperature relative to the start of the session. The boxes represent the standard error, the vertical bars indicate the standard deviation between subjects, *=1 drop-out **= 2 drop-outs.
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2.3. Discussion Only four out of six subjects were able to complete the session while flying at 35ºC without cooling. All subjects were able to complete the other sessions. The mean body temperature and its increase were, as expected, higher during the warm conditions than during the neutral condition. Blowing ambient air over the body led to a reduction of the heat strain and a increase in comfort while flying under warm conditions. The cooling system that was used in this experiment assists the evaporation of sweat. This form of cooling will not reduce sweat loss. One should keep in mind that it is of great importance that the pilot is able to drink enough to keep his body fluid on a reasonable level. The results show that the cooling vest reduces thermal strain and improves performance. The improvement is small but significant. In conclusion, forced ventilation seems to provide a significant cooling effect on the subjects during a simulated flight. The flow of ambient air over the body led to an increased evaporation of sweat and thereby cooled the body. Wearing the air-cooling vest can increase flight performance and thermal comfort of the pilots in hot environments.
3. Clothing fit In the previous chapter we showed that forced ventilation enhances cooling under protective clothing. However, during normal activities as walking or running, a standard amount of ventilation already exists, called the pumping effect. We asked ourselves if the ventilation rate could be improved by changing fit, in this case enhancing the microclimate volume [10].
3.1. Methods Nine male subjects participated in the study. The air volume between the skin and clothing was varied using metal rings in the inside of a combat jacket. These rings enlarged the volume by about 60%. The volume of the trapped air was determined reliably using 3D scanners [4]. Fig. 6 shows an example of a 3D scan with and without rings in the combat jacket. Since all subjects wore the same size of garment, the microclimate volume also varied due to subject variation in chest dimensions. The tracer gas method was used to determine ventilation [5]. The ventilation rate was measured during standing, walking, swinging arms and cracking arms.
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3.2. Results The impact of body movements on ventilation was more pronounced in the oversized jacket than in the normal fitting jacket. In the oversized jacket, the ventilation was about 200 l/min when standing still and 500 l/min when walking, as compared to 120 and 250 l/min for the normal fitting suit respectively. These finding were related to the microclimate volume, which averaged 26 litres in the normal jacket and 42 litres in the oversized jacket. No correlation was observed, however, between microclimate volume and ventilation between subjects, probably because the population was rather homogeneous in body dimensions. In conclusion, we observed that clothing fit has an impact on ventilation rate. Since ventilation rate is related to evaporative efficiency (chapter 3), fit thus impacts cooling rate.
Figure 6. Side view of a 3D scan of a nude subject (grey) with combat suit (green) and enlarged combat suit using metal rings (red).
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4. Conclusions Wearing protective clothing increases physiological and psychological strain of the wearer. Reduction of the heat strain may be achieved by personal cooling methods. Even the most simple method, blowing ambient air in the air gap between skin and clothing, proves to be effective. Increasing the volume of the trapped air may bring about further optimization. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
[10]
Boer, L.C. and VandeLinde, F.J.G. 1989. Psychological fitness with NBC Clothing. Report TNO TM 1989-12. TNO, PO Box 23, 3769 ZG Soesterberg, The Netherlands. Daanen, H.A.M., Tan, T.K., Koerhuis, C.L., Vander Horn, J. 2003. Performance degradation due to protective clothing in the heat. IEA conference 2003, Seoul. Daanen, H.A.M., Van Es, E., De Graaf, J. 2005. Heat strain and gross efficiency during endurance exercise after lower, upper of whole body precooling in the heat. Int. J. Sports Med. In press. Daanen, H.A.M., Hatcher, K., Havenith, G. 2005. Determination of clothing microclimate volume. In: Tochihara, Y., Ohnaka, T.: Environmental Ergonomics. Elsevier Ergonomics Book Series Volume 3. ISBN 0080444660. Pages 361 –368. Havenith, G., R. Heus, Lotens, W.A. 1990. Clothing ventilation, vapour resistance and permeability index: changes due to posture, movement and wind. Ergonomics 33(8), 989-1005. ISO 10551 (1995). Ergonomics of the thermal environment – assessment of the influence of the thermal environment using subjective judgement scales. ISO, Geneva. Malaplane, N.C. and Shaba, M.N. 2001. Comparison of functional performance of a soldier in full chemical and biological protection versus battle dress. International Journal of Industrial Ergonomics 27: 393-398. McLellan, T.M. 1993. Work performance at 40°C with Canadian Forces biological and chemical protective clothing. Aviation, Space and Environmental Medicine 64: 1094-1100. Reffeltrath, P.A., Den Hartog, E.A., Tutton, W., Buckley, R., Daanen, H.A.M. 2002. Efficiency of an individual air cooling system for helicopter crew. pp547-551. Environmental Ergonomics X. Papers from The 10th International Conference on Environmental Ergonomics. Fukuoka, Japan. 23-27 September, 2002. ISBN 49901358-0-6. Tan, T.K., Daanen, H.A.M., Brandsma, M.G. 2003. Influence of microclimate volume on motion generated convection. Report TM-03-B003. TNO, PO Box 23, 3769 ZG Soesterberg, The Netherlands.
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Intelligent Textiles for Personal Protection and Safety S. Jayaraman et al. (Eds.) IOS Press, 2006 © 2006 IOS Press. All rights reserved.
Author Index Boussu, F. Carpi, F. Chrzanowski, M. Daanen, H.A.M. De Rossi, D. Grancaric, A.M. Hertleer, C. Jayaraman, S. Kiekens, P. Klata, E.
65 55 41 133 55 v 89 v, 5, 21 v, 1 41
Koerhuis, C.L. Koncar, V. Krucińska, I. Lobnik, A. Lorussi, F. Park, S. Reffeltrath, P.A. Scilingo, E.P. Tognetti, A. Van Langenhove, L.
133 65 41 107 55 5, 21 133 55 55 89
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