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5
Design Challenge: PETMAN Surface Structure and Materials
This chapter addresses the feasibility of designing the mannequin surface or “skin” according to the following PETMAN design challenges:
3.2.2 The study will determine the feasibility of designing a PETMAN system to be compatible with all individual protection and ancillary equipment as well as weapon systems defined in 3.3.9-3.3.10.4. Areas to be addressed are donning/doffing and proper size/fit of the individual protection equipment. The PETMAN system design shall meet the appropriate 50th percentile male anthropometric measurements, as defined in DOD-HDBK-743A, Military Handbook Anthropometry of U.S. Military Personnel, to allow for the necessary fit/seal that each piece of protective equipment requires.
3.2.3 The study will determine the feasibility of designing a PETMAN system whose materials of construction will not be significantly degraded by exposure to both traditional chemical agents (T) and Toxic Industrial Chemicals (TICs) / Toxic Industrial Materials (TIMs) (O) and that can subsequently be decontaminated to negligible levels without adversely affecting the operation of the PETMAN system as defined in 3.3.11.
3.2.6 The study will determine the feasibility of designing a PETMAN system capable of operating in fixed environmental chamber conditions (T) and a range of environmental chamber conditions (O) as defined in 3.3.6.1-3.3.6.5.
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RELEVANT PETMAN REQUIREMENTS
PETMAN is conceived of as a surrogate for a soldier during the evaluation of an individual protection ensemble (IPE), specifically with respect to exposure to toxic industrial chemicals (TICs) and toxic industrial materials (TIMs). Just as a soldier would wear IPE, the PETMAN is expected to “wear” the IPE being tested; so it is important for the interaction between the PETMAN surface and the IPE to resemble the interaction between the soldier’s skin and the IPE. At the same time, the surface must also provide the necessary protection for the mannequin during harsh testing conditions.
The relevant PETMAN requirements (Box 5.1) and potential architectures and candidate materials for the PETMAN skin are discussed below.
According to the PETMAN requirements, the mannequin surface must perform the following key functions:
Protect the internals—all the mechanical, electric, and computing modules that are housed inside the mannequin—under harsh test conditions. This includes exposure to liquid and vapor chemical agents and chemical simulants.
Simulate human skin so that the interaction between the IPE and the PETMAN surface resembles the surface interaction between the soldier’s body and the IPE.
Facilitate the deployment of the sensors—preferably in a sensor network—for monitoring various parameters during testing.
Move with respiration to replicate the movement of the human chest wall with breathing.
Be easy and safe to decontaminate and, if necessary and feasible, be safely disposed.
Those key functions point to the need for a skin for PETMAN. It should be noted that the need for such a skin has not been explicitly stated in the Product Director, Test Equipment, Strategy and Support (PD TESS) requirements document.
THE PETMAN SKIN
The major characteristics of the PETMAN skin to meet the PETMAN requirements are breathability, sweatability, physiologic monitoring, resistance to chemical agents, usability, operating conditions, decontamination and disposability, and shape comformability.
Breathability defines the ability of the PETMAN skin to allow moisture vapor to escape from the body, whereas sweatability refers to its ability to
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BOX 5.1
Relevant PETMAN Requirements
3.3.5 The PETMAN system shall be compatible with current under-ensemble chemical breakthrough sampling technologies, procedures, and equipment as defined in Test Operations Procedure (TOP) 10-2-022, Chemical Vapor and Aerosol System-Level Testing of Chemical/Biological Protective Suits (T) and designed to enable integration with real-time (1-second increments) sampling technologies, procedures, and equipment (O). At a minimum, sampling locations shall be the same as those defined in TOP 10-2-022.
3.3.6 The PETMAN system operation shall not be affected by the following chamber environmental conditions.
3.3.6.1 Temperature: 90°F ± 2°F (T); −25°F to 125°F ± 1°F, measured every 5 minutes (O)
3.3.6.2 Relative Humidity: 80% ± 3% (T); 0-100% ± 1%, measured every 5 minutes (O)
3.3.6.3 Wind speed: 0-10 mph ± 10% (T); 0-161 mph ± 2 mph (O)
3.3.6.4 Pressure: 0.25 iwg chamber vacuum maintained ± 2%
3.3.6.5 Liquid and vapor chemical agents including all nerve and vesicant agents, as well as the chemical simulants, triethylphosphate and methyl salicylate.
3.3.9 The PETMAN system shall be compatible with the individual protection and ancillary equipment listed in 3.3.9.1-3.3.9.11. The PETMAN system shall be designed such that the individual protection equipment can be properly donned IAW the respective technical manuals.
3.3.11 The PETMAN system shall be capable of being decontaminated with no adverse effects on the operation of the system and such that there is no effect on the next iteration of test (T) or leaving negligible agent residual, as defined by 3X decontamination level in DA PAM 385-61, Toxic Chemical Agent Safety Standards, (O) on the PETMAN system.
3.3.13 The PETMAN system shall record the following system parameters over time: skin temperature, respiration rate, perspiration rate, and total mass (in nanograms) of chemical vapor that penetrates/permeates through the protective ensemble. The PETMAN system shall record the start and stop time of each motion in 1-second increments.
NOTE: T= threshold and O=objective
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transmit the moisture generated inside the PETMAN as human skin would. The skin should facilitate the integration of sensors to monitor physiologic measures, such as temperature and respiration rate, and to detect exposure to chemical agent, as well as TICs and TIMs. It should be resistant to chemical agents against which it is being tested. PETMAN should be usable in a variety of scenarios and with varied equipment, so its skin should not hinder handling of various weapons, moving around, or interaction with other components of the ensemble. It should withstand the various operating conditions of temperature, pressure, and environment to which PETMAN will be subjected to during the testing process. On completion of the test, the skin should be easy to decontaminate with such agents as bleach and hydrogen peroxide.1 Finally, shape conformability is critical to the successful deployment of PETMAN: the skin should easily conform to cover the various contours and parts of PETMAN and to facilitate the movement of the chest wall with breathing.
With the need for a PETMAN skin established and its characteristics defined, its architecture must be defined and potential materials for creating it identified.
The skin architecture is the structure of the skin that needs to be designed to meet the defined PETMAN performance requirements. Figure 5.1 shows three conceptual skin architectures considered.
In the first architecture, the skin consists of one layer. It could be porous so that it “sweats,” but it might be difficult to decontaminate if it is compromised during testing. Moreover, deploying sensors on the surface might be difficult because the sensors would need a mechanism for adhering to the surface; the sensors may also have to be powered, and they must communicate with the PETMAN sensor-controller module, necessitating the incorporation of wires or other devices.
In the second architecture, an outer skin is proposed to cover the PETMAN surface. This architecture overcomes the issues of decontamination (and disposal, if necessary) and deployment of sensors associated with the single-layer architecture. Through the proper selection of materials for the outer skin, it could be made soft to simulate the properties of human skin. However, if the soft skin and the surface skin are compromised, toxic agents could enter PETMAN and damage the internals.
To address the latter hazard, an impervious inner layer is proposed as shown in the third architecture. The third layer would be inside the PETMAN surface skin and provide an additional layer of protection to minimize contamination of the PETMAN internals.
Table 5.1 shows a comparative analysis of the three skin architectures
1
DA PAM 385–61 Toxic Chemical Agent Safety Standards, 27 March 2002, Department of the Army Pamphlet 385-61, http://www.army.mil/usapa/epubs/pdf/p385_61.pdf, pp. 18-21.
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FIGURE 5.1 Conceptual architectures for the PETMAN skin: (a) one layer; (b) two layers; and (c) three layers.
based on a set of key evaluation criteria: degree of protection, ease of decontamination and disposal, ease of sensor deployment and reconfiguration, and manufacturability. A ranking scheme of H, M, and L (high, medium, and low) is used. As shown in the table, the one-layer architecture offers the lowest degree of protection and is difficult to decontaminate. The deployment of sensors on the surface is also difficult. However, from a manufacturabilty standpoint, it would be the easiest to fabricate.
The three-layer architecture offers a higher degree of protection than the two-layer architecture, but it would be more difficult to manufacture PETMAN in that architecture than in the two-layer architecture. By weighting the criteria (that is, using a weighted-priority matrix approach), the
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TABLE 5.1 Comparison of Possible PETMAN Skin Architectures
Number of Layers
Degree of Protection
Ease of Decontamination and Disposal
Ease of Sensor Deployment and Reconfiguration of Positions
Manufacturability
One
L
L
L
H
Two
M
H
H
H
Three
H
H
H
L
NOTE: L = little or no capability, M = medium capability, H = highest capability or most desirable.
relative merits of the different architectures can be thoroughly evaluated, and such an approach is recommended during the design and development of PETMAN. In the present analysis, manufacturability is considered to affect the success of PETMAN substantially, so it is weighted more than degree of protection, which is another evaluation criterion.
CURRENT TECHNOLOGY TO MEET SKIN DESIGN CHALLENGES
On the basis of the comparative analysis, the preferred architecture of the PETMAN skin (of the three considered) would be two layers: a porous surface skin to protect the internals and an outer soft skin in which a sensor network can be easily deployed.
Surface Skin
The material for the surface skin must protect the PETMAN internals and facilitate sweating and zoned heating of the different regions. As discussed in Chapter 2, Measurement Technology Northwest (MTNW) has a metal porous skin (Figure 5.2) that has been used successfully in commercial mannequins for simulating sweating and providing zoned heating. It is a potential candidate for the PETMAN surface skin.
Soft Skin
In addition to having the characteristics of the PETMAN surface skin, the soft skin must facilitate the deployment of sensors, be easily decontaminated, and provide a surface like human skin for the IPE. An extensive review of the literature on artificial skin has led to the conclusion that developments in alternatives to skin are biological tissue-based and that the resulting structure typically requires a living body to sustain it and continue to grow. One of the best examples of such tissue-based artificial
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FIGURE 5.2 MTNW’s metal porous skin, a potential candidate for PETMAN surface skin.
SOURCE: Rick Burke, Measurement Technology Northwest. http://www.mtnw-usa.com.
skins is EpiDerm™ from Matek Corporation.2 A conversation with a representative of the company led to the conclusion that no “polymer-based” surrogate could be an ideal substitute for human skin. Hence, the design challenge is to investigate and identify polymeric materials that would come close to human skin in physical, mechanical, and chemical properties and would meet the PETMAN performance requirements discussed earlier. During the course of the study, it was difficult to find published data on the physical and mechanical properties of human skin. Box 5.2 describes the structure and some properties of human skin.
The first step in selecting candidate materials for soft skin is to identify the specific properties (especially properties that can be measured in the laboratory) that will bear on the requirements. For example, breathability will be affected both by the material type and by the porosity of the structure used for the soft skin. The key design characteristics that must be considered in selecting materials for the soft skin include: porosity, flexural
2
Epiderm Technical Specifications. MatTek Corporation. http://www.mattek.com/pages/products/epiderm/specification. Accessed June 15, 2007.
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BOX 5.2
Human Skin: Structure and Properties
Human skin is a heterogeneous tissue composed of three superimposed layers that are intimately connected but distinct in their nature, structure, and properties (Figure 5.3).a The epidermis—mainly the stratum corneum—is concerned with protecting the organism from the environment. The fi brous dermis is a viscoelastic envelope that, with the hypodermis (the subcutaneous layer), plays an essential role in protecting the skin from mechanical stress. The mechanical function of the skin is the expression of the biomechanical nature of its components and their structural organization. Skin also keeps the human hydrated and cools humans with sweat.
FIGURE 5.3 Structure of human skin.
SOURCE: Adapted from http://nihseniorhealth.gov/skincancer/faq/faq3b_popup.html.
aEscother, C., Rigal, J., Rochefort, A., Vasselet, R., Leveque, J., and Agache, P. G., “Age-related Mechanical Properties of Skin: An in vivo Study,” Journal of Investigative Dermatology, Vol. 93, No. 3, 1989, pp. 353-357.
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rigidity, abrasion resistance, manufacturability, form factor, surface hardness, chemical properties, and tensile properties.
The tensile properties and abrasion resistance of the material affect the durability of the soft skin, and its flexural rigidity influences shape conformability. Surface hardness will affect the interaction between PETMAN and the IPE; the chemical properties of the material define its resistance to TICs and TIMs and hence determine whether PETMAN requirements can be accomplished. The manufacturabilty of the material affects the eventual production of PETMAN. The form factor is the way in which the material can be used to create the soft skin, such as a coating, a casting, or a formfitting layer (fabric or garment) on the PETMAN surface skin.
There are two approaches to achieving the PETMAN soft skin. The first is to use the design characteristics discussed above and engineer or create the materials for the soft skin. The second, more pragmatic approach, which has been adopted here, is to identify existing materials and carry out a comparative evaluation of their properties to select the materials that best meet the requirements. All the characteristics are important, but a subset (chemical properties, porosity, manufacturability, and form factor) are considered below in the evaluation process for selecting suitable materials for realizing the PETMAN soft skin.
Some potential candidate materials for the PETMAN soft skin are polyester, nylon, polyurethane, polyurethane in the form of spandex, expanded polytetrafluoroethylene (ePTFE) membranes and powder, and ePTFE-based fabrics. Some of the important properties of these materials are presented below.
Polyester: Polyester is made from polyethylene terephthalate (PET) and ariants, such as polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT). Its tensile and abrasion properties are excellent, and it has high elastic recovery. Polyester has excellent resistance both to acids and alkalis, and it can be bleached with chlorine or oxygen bleach. It is used widely in traditional apparel and carpets.
Nylon: Nylon was the first synthetic polymeric fiber. It is a polyamide and can be made from hexamethylene diamine and adipic acid (nylon 6,6) or from caprolactam (nylon 6). It is strong and durable and has good elastic recovery properties. Nylon has excellent resistance to alkali and chlorine bleaches and is damaged by strong acids. It is used extensively in carpets, hosiery, and sportswear.
Polyurethane and spandex: Polyurethane offers the elasticity of rubber combined with the toughness and durability of metal. It can be manufactured in a variety of hardness, or durometers, and can elongate up to 800 percent
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and return to its original dimension without a substantial loss of memory.3 Polyurethane is highly resistant to heat, cold, and aging. It has excellent long-term stability in water and is resistant to swelling and deterioration in temperatures as high as 80°C. It is resistant to oil and solvents and outperforms metal in chemical resistance. Those properties allow polyurethane to be used in some of the harshest of environments with minimal deterioration. It can also be bonded to metal, wood, or fabric.4
Spandex, known under the trade name Lycra®, which is made up of a long-chain polyglycol combined with a short diisocyanate, contains at least 85 percent polyurethane. It is known as an elastomer because it can be stretched to some degree and recoils when released. Because of its high stretch (600 percent), it is used in a wide variety of apparel products, especially form-fitting garments that take advantage of its unique elastic recovery properties, such as swimsuits, exercise gear, and undergarments.
Expanded polytetrafluoroethylene (ePTFE): PTFE is a polymerized tetrafluoroethylene, known for its chemical inertness, high thermal stability, low coefficient of friction, and other distinctive properties. When PTFE is stretched rapidly, it becomes a strong, water resistant yet breathable microporous material referred to as ePTFE, which is the key component of GORE-TEX® membrane.5 The ePTFE structure is combined with an oleophobic, or oil-hating substance that allows vapor to pass through but prevents contaminating substances—such as body oils, cosmetics, insect repellents, and food substances—from penetrating. In addition, ePTFE is known to be chemically resistant to virtually all industrial chemicals, including acids, alcohols, aldehydes, amines, bases, esters, ethers, halogenated hydrocarbons, hydrocarbons, ketones, and polyalcohols.6
Another variant incorporating ePTFE, is the GORE CHEMPAK®, which combines a chemical protective polymer with an ePTFE. This fabric is also liquid-proof and air-impermeable and affords additional protection against liquid chemical-warfare agents and wind-driven agents in aerosol, vapor, and particulate form.
Table 5-2 shows a comparative assessment of these materials according to the major criteria identified earlier.
A key characteristic of PETMAN skin to meet the requirements is that it must be able to be decontaminated with the procedure outlined in
3
Polyurethane. Bay Plastics. http://www.bayplastics.co.uk/Product%20Materials/prod-poly-urethane.htm. Accessed June 15, 2007.
4
Polyurethane—Features and Benefits. Elastochem Specialty Chemicals, Inc. http://www.elastochem-ca.com/poly.html. Accessed June 15, 2007.
5
GORE-TEX. www.goretex.com. Accessed June 15, 2007.
6
GORE Protective Vents Glossary. GORE. http://www.gore.com/en_xx/products/venting/technical/membranevents_glossary.html#. Accessed June 15, 2007.
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TABLE 5-2 A Comparison of Potential Materials for PETMAN Soft Skin
Material
Chemical Resistant Properties
Breathability
Ease of Decontamination and Disposal
Surface Properties
Usability (Operating Conditions)
Polyester
M
L
M
M
L
Nylon
L
L
L
M
L
Polyurethane (including spandex)
H
M
H
H
H
ePTFE (including its variants)
H
H
H
H
H
NOTE: L = little or no capability, M = medium capability, H = highest capability or most desirable.
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Toxic Chemical Agent Safety Standards.7 Polyurethane and ePTFE are far superior to polyester and nylon in chemical resistant properties, for which they are rated high in the table. Nylon is affected by strong acids and so is rated low. Polyurethane and ePTFE are both highly inert chemically and are assigned a rating of high to denote the ease with which they can be decontaminated. Polyester can be decontaminated with both chlorine and oxygen bleaches, whereas only chlorine bleach can be used on nylon. The surface characteristics of polyurethane and ePTFE are superior to those of nylon and polyester. Similarly, the ability of polyurethane and ePTFE to withstand extreme operating conditions (such as those to which PETMAN will be subjected) merits the ratings shown in the table in comparison with those for polyester and nylon.
Form Factor for PETMAN Soft Skin
The PETMAN soft skin can take one of three forms: It can be a coating on the surface skin, for example, using polyurethane8; it can be a casting that is bonded to the surface skin with a breathable adhesive9; or it can be a form-fitting layer on the surface skin in the form of a fabric or garment, as is the case with NEWTON, the mannequin from MTNW.10 A comparative evaluation of the three options based on a set of critical criteria is shown in Table 5.3.
From the viewpoint of ease of sensor deployment, a form-fitting layer provides the greatest ease because the sensors could potentially be integrated into the structure. In contrast, deploying the sensors (especially providing power and communication) would not be easy on smooth surfaces realized by coating and casting. A form-fitting layer is also better than a coating or casting when it comes to ease of decontamination and disposal.
A surface coating or casting would not affect the movement of PETMAN around the joints in the legs, arms, and so on. In comparison, a form-fitting layer, if not properly designed, potentially could impair the movement in the joints; and the form-fitting layer could be subjected to deformation from repeated bending and flexure. With respect to facilitating chest-wall movement, the form-fitting layer would be the most accommodating. Finally, from a manufacturability standpoint, a form-fitting layer would be the easiest to manufacture and also the most economical. Thus,
7
U.S. Army. DA PAM 385–61 Toxic Chemical Agent Safety Standards, 27 March 2002, Department of the Army Pamphlet 385-61, http://www.army.mil/usapa/epubs/pdf/p385_61.pdf, pp. 18-21.
8
Sakhpara, U.S. Patent 4,942,214, 1990.
9
Driskill U.S. Patent 4,925,732, 1990.
10
Burke, R., Presentation at the 3rd PETMAN Meeting, April 2007 (see Appendix D).
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TABLE 5.3 Comparison of Possible Material Form Factor for PETMAN Soft Skin
Form Factor
Ease of Sensor Deployment and Reconfiguration of Positions
Ease of Decontamination and Disposal
PETMAN Joints (Arms, Legs, and so on)
Chest-Wall Movement
Manufacturability
Coating
L
L
H
M
M
Casting (bond with breathable adhesive)
L
M
H
L
M
Form-fitting layer
H
H
M
H
H
NOTE: L = little or no capability, M = medium capability, H = highest capability or most desirable.
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on the basis of this structured evaluation, a potential form factor for the PETMAN soft skin is a form-fitting layer.
Architecture of PETMAN Soft Skin
The final step is to identify a potential configuration of material type and form factor for the PETMAN soft Skin. Table 5.4 shows the composite ranking of the various combinations of form factor—casting and a formfitting layer—and the five choices for materials, including ePTFE and its variants, and polyurethane and its variant spandex.
With the powdered form of ePTFE,11 it is possible to produce a casting, but use of ePTFE in a form-fitting membrane would be preferable. In Table 5-3, a form-fitting layer was the preferred form factor. The ePTFE-based CHEMPAK fabrics are available only in fabric form, so they cannot be used for creating a casting. Polyurethane can be easily cast compared with its use as a form-fitting layer). Spandex is ideally suited for use in a form-fitting layer (compared with casting). A form-fitting layer has the additional advantage of serving as the infrastructure for the deployment of sensors, potentially using the wearable-motherboard paradigm.
In Table 5-2, ePTFE was identified as the preferred material over polyurethane. Therefore, on the basis of both form factor and properties of materials, a form-fitting layer of ePTFE-based materials is the preferred configuration for the PETMAN soft skin. Because the CHEMPAK fabrics have additional chemical-protective characteristics, they could be an ideal choice for the PETMAN soft skin. Alternatively, a spandex-based form-fitting layer could serve as another choice for soft skin.
Integrating the PETMAN Sensing System and Skin
The next step in the process of designing a PETMAN will be to identify an effective means of integrating the skin into the PETMAN system. In particular, it is important to consider integrating the skin and sensors identified in Chapter 3. Analysis of the requirements leads to the following conclusions:
Different types of sensors are needed to monitor different characteristics.
Different numbers of sensors of each type may be needed for computing a single characteristic
The sensors need to be positioned in different locations on PETMAN to acquire the proper signals.
11
Dolan et al., USP 5,646,192, 1997.
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TABLE 5.4 Soft-Skin Configuration: Form Factor and Materials Analysis
Material Options
Form Factor
ePTFE and Variants
CHEMPAK® Ultra Barrier
CHEMPAK® Selectively Permeable
Polyurethane
Spandex
Casting
M
N/A
N/A
M
L
Form-fitting layer
H
H
H
L
H
NOTE: L = little or no capability, M = medium capability, H = highest capability or most desirable.
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Different subsets of sensors may be used at different times, necessitating easy attachment and removal.
The sensors and the manner in which they are deployed should neither impair the mobility of the PETMAN nor affect the interaction between PETMAN and the IPE.
Sensors may need to be powered.
Sensors need to communicate with the PETMAN sensor control module.
Thus, what is needed is the design and implementation of a network of sensors on PETMAN to meet the threshold and objective requirements. Smart textiles or wearable electronic systems provide a possible platform for such a network.12 For example, the Smart Shirt uses optical fibers to detect physiological signals and movement.13
Figure 5.4 shows the architecture of the imbedded sensor network. The base fabric provides the necessary physical infrastructure and is made of typical textile fibers chosen according to the intended application. The optical fiber integrated into the structure provides the infrastructure for carrying information through the fabric and is used for identifying projectile penetration with optical time-domain reflectometry. The interconnection technology has been used to create a flexible conductive framework to plug in sensors for monitoring a variety of vital signs. This technology can potentially be adopted for deploying sensors on PETMAN; the optical fibers in the fabric can serve as the infrastructure for the fiber-optics-based sensors, and the conductive-fiber network can provide the power and communication capabilities required by the other types of sensors on PETMAN.
CONCLUSIONS AND RECOMMENDATIONS
Analysis of the PETMAN surface requirements and potential solutions to meet the requirements resulted in the following conclusions and recommendations:
Conclusion 5-1: The need to simulate the interaction of human skin with the IPE has not been specified in the PETMAN requirements. However, since the PETMAN is conceived of as a surrogate for a soldier during the evaluation of IPE, it is important for the interaction
12
Service, R. F. 2003. News Focus Technology: Electronic Textiles Charge Ahead. Science 301(5635):909-911; Park, S., and S. Jayaraman. 2003. Smart Textiles: Wearable Electronic Systems. MRS Bulletin (August 2003):585-591.
13
See http://www.sensatex.com/index.php/smartshirt-system Accessed August 16, 2007.
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FIGURE 5.4 The architecture of an embedded sensor network.
SOURCE: S. Jayaraman, Georgia Institute of Technology.
between the PETMAN surface and the IPE to resemble the interaction between the soldier’s skin and the IPE.
Recommendation 5-1: Simulation of the interaction of human skin with the IPE should be added as an objective PETMAN requirement.
Conclusion 5-2: Various methods exist for achieving the threshold and objective PETMAN requirements that include a mannequin surface consisting of multiple layers of skin, such as an inner skin that protects internal mechanical and electrical components and an outer soft skin that is in contact with the IPE.
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Conclusion 5-3: Various methods exist for the deployment of sensors on PETMAN, such as sensor-embedded textiles.
Recommendation 5-2: There should be a multilayer skin architecture for PETMAN to meet the threshold and objective requirements, such as an inner porous skin and an outer soft skin with an embedded sensor network.
Conclusion 5-4: Various materials exist for the inner skin to meet the threshold and objective requirements of PETMAN, such as a metal porous skin from Measurement Technology Northwest that perspires and provides zoned heating.
Conclusion 5-5: Various materials exist for the outer soft skin in contact with the IPE, such as expanded polytetrafluoroethylene and polyurethane (spandex).
Conclusion 5-6: Extensive data on the performance characteristics of the metal porous skin and ePTFE-based materials were not available, especially those related to the chemical and biologic protection characteristics of CHEMPAK.
Recommendation 5-4: The performance characteristics and metrics claimed by the commercial developers (vendors) of metal porous skin and ePTFE-based fabrics and materials should be validated as part of the PETMAN design and development process.
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