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3 Design Challenge: Mannequin Under-Ensemble Sensing This chapter mainly discusses the following two PETMAN design challenges: 3.2.4 The study will determine the feasibility of designing a PETMAN system with an integrated under-ensemble sampling system that will al- low for the collection of agent breakthrough data in real time (1-second increments). 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 126.96.36.199-188.8.131.52. The design, fit, or size of the protective garment will influence chemical- agent penetration. When worn, clothing is subjected to pressure differentials across the garment due to breathing, wind, or the bellows effect created by body movement, which may force chemical-warfare agent (CWA) or toxic industrial chemicals (TICs) vapor or aerosol through the clothing fabric and closures. Bending and moving stresses clothing, particularly over the joints. To determine penetration of chemical-protective ensembles by chemi- cal vapor or aerosol, it is necessary to test the entire suit system, including seams, closures, and areas of transition with other protective equipment, that is, at the ankles, waist, wrists, and neck. In addition, aspects of the PETMAN tests such as the environmental conditions of the test chamber will also impact CWA penetration through the soldier IPE. 57
58 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT In addition to the two design challenges given above, consideration will also be given to the PETMAN design challenge concerning mannequin sup- port, which also impacts the feasibility of CWA sampling technologies: 3.2.1 The study will determine the feasibility of designing a PETMAN system to be tethered (T) or free standing/self-contained (O). A tethered PETMAN system design must not compromise the integrity of the individ- ual protection ensemble equipment being tested on the PETMAN system. If a tethered design is selected the design must also minimize the impact to the whole ensemble operation. Relevant PETMAN Requirements The relevant PETMAN requirements (Box 3.1) and various technolo- gies for the detection of CWAs for potential use in the PETMAN manne- quin are discussed below. Other Considerations Some conditions in addition to the PETMAN system design challenges and requirements designated above should also apply to ensure proper functioning of the sensor technology in the context of all other PETMAN requirements. The technology should be: â¢ Unaffected by perspiration (water vapor) beneath the garment ensemble â¢ Unaffected by any potential interferents from garment material or residual decontamination cleanser and chemicals off-gassing â¢ Packaged in a durable device that can withstand rough handling and repeated use â¢ Portable enough to be conveniently placed in different locations on the test mannequin and beneath the protective garment â¢ Unaffected by âfalse-positiveâ readings (for example, readings that result from residual volatile additives in the protective-garment ma- terial, decontamination chemicals and cleansers, or from moisture interference) â¢ Currently available in a usable product form â¢ Have minimal impact on internal airflow within the suit
DESIGN CHALLENGE: MANNEQUIN UNDER-ENSEMBLE SENSING 59 Box 3.1 Relevant PETMAN Requirements 3.3.2 The PETMAN system shall be capable of operation for twelve (12) hours prior to requiring operational maintenance, three (3) months prior to preventive maintenance and six (6) months prior to calibration. (T) The PETMAN system shall be capable of operation for twenty-four (24) hours prior to requiring operational maintenance, six (6) months prior to preventive maintenance and twelve (12) months prior to calibration. (O) Operational maintenance is defined as the required maintenance procedures to prepare the PETMAN system for each test trial, for example, filling a perspiration reservoir, changing agent samplers or decontami- nation before the next trial. Preventive maintenance is defined as a maintenance event performed prior to a failure in order to prevent its occurrence. 3.3.5 The PETMAN system shall be compatible with current under ensemble chemical breakthrough sampling technologies, procedures, and equipment as de- fined 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 (see Figure 3.1 and Table 3.1). 3.3.6 The PETMAN system operation shall not be affected by the following cham- ber environmental conditions. 184.108.40.206 Temperature: 90Â°F Â± 2Â°F (T); â25Â°F to 125Â°F Â± 1Â°F, measured every 5 minutes (O) 220.127.116.11 Relative Humidity: 80% Â± 3% (T); 0-100% Â± 1%, measured every 5 minutes (O) 18.104.22.168 Wind speed: 0-10 mph Â± 10% (T); 0-161 mph Â± 2 mph (O) 22.214.171.124 Pressure: 0.25 iwg chamber vacuum maintained Â± 2% 126.96.36.199 Liquid and vapor chemical agents including all nerve and vesicant agents, as well as the chemical simulants, triethylphosphate and methyl salicylate. 3.3.12 The PETMAN system shall utilize as many common commercially available parts and/or components as possible. 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 mo- tion in 1 second increments. NOTE: T=threshold and O=objective
60 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT FIGURE 3.1 Sampling locations for the Passive Absorbent Devices (PADs) for Man-in-Simulant Test (MIST); Chemical Vapor and Aerosol System-Level testing of chemical/biological protective suits. SOURCE: U.S. Army Developmental Test Command Test Operations Procedure (TOP) 10-2-022. December 14, 2005. Chemical Vapor and Aerosol System-Level 3-1 Testing of Chemical/Biological Protective Suits. DTIC AD No. ADA440290. Current Detection Technologies A chemical sensor uses chemical (and possibly biologic) reactions to detect and quantify a specific analyte. Such devices are usually self-con- tained and have a sorptive surface that interacts chemically with the analyte of interest (commonly a polymeric membrane or coating that contains a specific low-molecular-weight âdoping agentâ), a transducer that detects the chemical event occurring between the surface and the analyte, and sup- porting electronics or software that amplifies and reports the output signal
DESIGN CHALLENGE: MANNEQUIN UNDER-ENSEMBLE SENSING 61 Table 3.1 Passive Absorptive Device (PAD) Placement Location Descriptions; Individual Protective Equipment for Selectively Permeable Membrane Materials Man-in-Simulant Test, as Shown in Figure 3.1 Position Numbera Description P21 Scalp P22 Left Ear P24 Chin P25, PD25b Nape P26 Armpit P27 Inner Upper Arm P28 Outer Upper Arm P29 Forearm, Volar P30 Mid Back P31 Abdomen P32, PD32b Buttocks P33, PD33b Groin P34 Crotch/Scrotum P35 Inner Thigh P36, PD36b Inner Shin P37 Blank Transport Sample for Quality Control (QC) P38 Spike Transport Sample for QC Don Dress Area Doff Undress Area P90 Nose Cup P91c Mask P92 Glove (Hand) P93 Boot (Foot) aSeeFigure 3.1. bIndicatesduplicate PSD at these locations. cPSD placed in transport case to monitor cross-contamination. SOURCE: U.S. Army Developmental Test Command Test Operations Procedure (TOP) 10- 2-022. 14 December 2005. Chemical Vapor and Aerosol System-Level Testing of Chemical/ Biological Protective Suits. DTIC AD No. ADA440290. from the transducer. The sorptive material is probably the most critical component of the sensor in terms of determining the sensitivity and selectiv- ity, regardless of the transducer. â Grate, J. W., and D. A. Nelson. 2003. Sorptive Polymeric Materials and Photopatterned Films for Gas Phase Chemical Microsensors. Proceedings of the IEEE 91(6):881-889.
62 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Table 3.2 Overview of Technologies Currently Available for Detection of CWAs, TICs, and TIMs Technology Principle Chemicapacitor technology An array of polymer-filled chemically sensitive capacitors, detects the presence of vapors in the air. A single 2 x 5-mm chip has the potential to contain an array of up to eight capacitors. A more detailed discussion is presented below. Electrochemical sensors These sensors operate by reacting with the gas or vapor of interest and producing an electric signal that is proportional to the gas or vapor concentration. Fiber-optics-based sensor A polymer-, porphyrin-, or enzyme-treated substrate is subjected to a specified range of light. The response of the detection system to the nonabsorbed radiation determines the types and amounts of chemical agents present. A more detailed discussion is presented below. Flame-ionization detector (FID) A FID is an ion detector that uses an air-hydrogen flame to produce ions. As components elute from the gas chromatographâs column, they pass through the flame and are burned, producing ions. The ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced and the greater the current. Many technologies exist for detecting CWAs, TICs and TIMs, and have been reviewed extensively elsewhere. A list of some potential de- tection technologies for PETMAN is given in Table 3.2 and evaluated in Table 3.3. Three of these detection transducers at various stages of â See the following reviews and others for more information on chemical and biological sensing technologies: Dadik, O., W. H. Land, Jr., and J. Wang. 2003. Targeting Chemical and Biological Warfare Agents at the Molecular Level. Electroanalysis 15(14):1149-1159; Seto, Y., M. Kanamori-Kataoka, K. Tsuge, I. Ohsawa, K. Matsushita, H. Sekiguchi, T. Itoi, K., Y. Sano, and S. Yamashiro. 2005. Sensing Technology for Chemical-Warfare Agents and Its Evaluation Using Authentic Agents. Sensors and Actuators, B: Chemical 108:193-197; Sun, Y., and K. Y. Ong. Detection Technologies for Chemical Warfare Agents and Toxic Vapors, CRC Press (2004).
DESIGN CHALLENGE: MANNEQUIN UNDER-ENSEMBLE SENSING 63 Table 3.2 Continued Technology Principle Ion-mobility spectrometer (IMS) A radioactive source is used to ionize the target gas; the resulting ions are directed into a drift chamber where they are separated by mass and charge. The amount of ions of each mass or charge collected determines the amount and type of gas or vapor molecules present. Passive adsorptive devices (PADs) PADS technology uses packets of TenaxÂ® that adsorb the agent simulant methyl salicylate. Afterward, the simulant is desorbed from the Tenax and quantified. This technique is currently used in the Man-in-Siumulant-Test. Photoionization detector (PID) A PID uses an ion detector having high-energy photons, typically in the UV range, to produce ions. As components elute from the gas-chromatograph column, they are bombarded by high-energy photons and are ionized. The ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced and the greater the current. Surface acoustic wave (SAW) Detection is based on the change in the propagation of an acoustic wave over a piezoelectric substrate treated with a polymeric coating. A more detailed discussion is presented below. developmentâchemicapacitor, fiber-optics, and surface acoustical wave (SAW)âwere chosen as illustrative examples for evaluating the feasibility of the PETMAN requirements in more detail. The chemicapacitor technol- ogy is commercially available but not widely used, fiber-optics based is not commercially available but has the potential to be developed with the next year, and SAW based is commercially available and widely used in many application areas. In Tables 3.4 through 3.6 the three technologies and the current passive absorptive devices (PADs) currently used in the MIST are compared based on how they all address the PETMAN requirements. Chemicapacitor Detection Technology Chemicapacitor sensors measure the change in dielectric constant of selectively adsorbing materials such as a polymer or single-walled carbon
64 Table 3.3â Ratings of Detection Technology for Various Characteristics (L = little or no capability, M = medium capability, H = highest capability or most desirable) Electro- Chemicapacitor chemical Fiber-Optics FID IMS PADs PID SAW Range of CWAs detected H L H L H Unknown M H Range of TICs detected L M H L M Unknown M L Selectivity for agents H M H L L Unknown L H detected Sensitivity to CWAs H L M-H L H Unknown L H (depends on system) Relative size or footprint M L H L L H L M (smaller is more desirable) Start-up time (shortest time H M H M M H M M is most desirable) Response time (â¤ 1 s is M M H M M L M M most desirable) Potential for wireless Yes Yes Yes Yes Yes Not powered Yes Yes power source
Table 3.4 â Comparison of Various Detection Technologies with PADs in Meeting Threshold PETMAN Program Requirements Requirement Chemicapacitor Fiber Optics PADs SAW Commercialized Yes No No Yes Can be placed at all sampling locations defined in Yes Yes Yes Yes TOP 10-2-022 (see Section 3.3.5) Capable of detecting specified agentsânerve agent Yesa Yes Yes Yes GB and vesicant HDâand their simulants, triethyl phosphate and methyl salicylate, respectively (see Section 3.3.6) Capable of detecting nanogram levels of agent or Yes Yes Not applicable Yes simulant penetration or permeation Capable of operating for 12 hours before requiring Yesb Yes Not applicable Yes operational maintenance, three months before preventive maintenance, and six months before to calibration (see Section 3.3.2) Compatible with current under-ensemble chemical- Yes Yes Yes Yes breakthrough sampling technologies, procedures, and equipment as defined in TOP 10-2-022 (see Section 3.3.5) Operational at (not affected by) a temperature of Yes Yes Yes Yes 90 Â± 2Â°F (see Section 188.8.131.52) aLimits of detection have to be determined or confirmed. bLong-term testing has yet to be performed. 65
66 Table 3.5 Comparison of Various Detection Technologies to Meet Objective PETMAN Program Requirements Requirement Chemicapacitor Fiber Optics PADs SAW Powered in such a manner that it does not require Yes Yes Yes Yes tethering to a power source, for example, battery- powered and wireless (see Section 3.2.1) Capable of operating for 24 h before requiring Yesa Yes Not applicable Yes operational maintenance, 6 months before preventive maintenance, and 12 months before calibration (see Section 3.3.2) Able to detect and report agent or simulant Yes Yes No No permeation or penetration in real time in 1 second increments (see Section 3.3.5) Operational at (not affected by) temperatures of â25 Unknown Unknown Unknown Unknown to 125 Â± 1Â°F (see Section 184.108.40.206); note, however, (known to operate at (known to that if a mannequin skin that evolves metabolic heat 32-125Â°F) operate at is developed, a temperature of â25Â°F may not be 14-104Â°F) reached aLong-term testing has yet to be performed.
Table 3.6 Comparison of Various Detection Technologies to Address âOther Considerationsâ for the PETMAN Program Consideration Chemicapacitor Fiber Optics PADs SAW Immune to potential effects of perspiration or water Yes Likelya Yes Yes vapor beneath garment ensemble to be tested Immune to potential interferents from off-gassing Yes Likelya Possibly no Yes from polymers (from which garments may be made), decontamination chemicals, and cleansers Packaged in durable device that can withstand Yes Yes Yes Yes rough handling and repeated use Portable enough to be conveniently placed in Yes Yes Yes Yesb different location on test mannequin and beneath garment? Results in âfalse-positiveâ reading for test agents Noc Noc Unknown No (GB, HD, or simulants) aAdditional testing must be performed to confirm that sensor is not affected by perspiration or water vapor or by components that may off-gas from protective garment. bAdditional development work will be necessary to reduce âfootprintâ and profile of device. cAdditional testing must be performed to confirm that no âfalse-positiveâ readings occur. 67
68 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT nanotube, and are capable of detecting organic vapors, and inorganic gasesâincluding CWAs and TICS. Early sensors measured capacitive hu- midity. Current commercially available chemicapacitor sensor arrays con- tain 8 to 16 sensors on a 2 Ã 5-mm chip, which allows for a small, portable detector package (with electronics measuring about 2.5 Ã 2 Ã 1 in.). Key characteristics of chemicapacitor sensing based on the references cited are given below. Dynamic Range and Detection Limit: Sensitivity to most VOCs is in the low parts per million (ppm) range. Limits vary with the vapor pressure of the target analyte. Response Time: The mass-transfer limitations of the thick chemoselective dielectric material (~1 Âµm) may cause a sensor to appear slower than it is. Under optimal conditions in the laboratory, the chemicapacitors demon- strate a response time of less than 1 s and a recovery time of 1-2 s after exposure to many vapors. Response over Temperatures and Humidities: Chemicapacitor sensors have been tested over a temperature range of 32-125oF and over the full range of relative humidity (0-100% noncondensing). As in all polymer-based technologies, sensitivity is a function of the temperature and vapor pressure of the target. Fiber-Optics-Based Detection Technology Fiber-optics-based chemical agent detection uses optical spectroscopy to detect chemicals absorbed to an active polymer-, porphyrin-, or enzyme-treated substrate. Optical signals pass to a detector by way of â Snow, E. S., F. K. Perkins, E. J. Houser, S. C. Badescu, and T. L. Reinecke. 2005. Chemical Detection with a Single-Walled Carbon Nanotube Capacitor. Science 307(5717):1942-1945. â Patel, S. V., T. E. Mlsna, B. Fruhberger, E. Klaassen, A. Cemalovic, and D. R. Baselt. 2003. Chemicapacitive Microsensors for Volatile Organic Compound Detection. Sensors and Actua- tors, B: Chemical 96(3):541-553. â Mlsna, T. E., S. Cemalovic, M. Warburton, S. T. Hobson, D. A. Mlsna, and S. V. Patel. 2006. Chemicapacitive Microsensors for Chemical Warfare Agent and Toxic Industrial Chemi- cal Detection. Sensors and Actuators, B: Chemical 116(1-2):192-201. â Delapierre, G., H. Grange, B. Chambaz, and L. Destannes. 1983. Polymer-Based Ca- ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ pacitive Humidity Sensor: Characteristics and Experimental Results. Sensors and Actuators 4:97-104. â Seacoast Science, Inc.: http://www.seacoastscience.com/Downloads/Seacoast_White_Paper_ DEC%202006.pdf, accessed August 28, 2007. â Wolfbeis, O. S. 2004. Fiber-Optic Chemical Sensors and Biosensors. Analytical Chemistry. 76(12):3269-3283.
DESIGN CHALLENGE: MANNEQUIN UNDER-ENSEMBLE SENSING 69 a single or bundle of optic fibers. The response of the detection system to the nonabsorbed radiation determines the types and amounts of chemical agents present. A key flexibility in the use of optical systems is the ability to incorporate optical fibers into the sensor system and allow one or more central sensor systems with fibers running to multiple locations in the mannequin. These systems are used in variety of ways. The committee heard talks about two different fiber-optics-based chemical agent sensing approaches (see Appendix D). One way is with multiple chemical coatings (sensors) on bundled fibers that have differential partitioning of the target analyte. Another way uses a single fiber interacting with a solid-state substrate.10 Bundled fiber sensors can be constructed with thousands of fibers allowing the use of hundreds of coating replicates, which improve signal-to-noise ratios. In addition, a single coating can be placed over all the fibers in a bundle to improve sensitivity and reaction time. Key characteristics of fiber- optic sensing based on the references cited are given below. Dynamic Range and Detection Limit: Some fiber-optics-based technologies can measure from 25 ng to over 1 Î¼g of gas, but this can vary with the fiber-optics system. Response Time: Under optimal conditions in the laboratory, the fiber- optics-based system has a response time of less than 1 s. False-Positive Readings: Preliminary laboratory testing suggests the absence of false-positive readings. Additional laboratory testing is needed. Response over Temperatures and Humidities: Preliminary laboratory test- ing suggests that fiber-optics-based systems can operate over a range of temperatures and humidities. Additional laboratory testing is needed. â Albert,K. J., and D. R. Walt. 2003. Information Coding in Artificial Olfaction Multisensor Arrays. Analytical Chemistry 75(16):4161-4167; Epstein, J. R., M. Lee, and D. R. Walt. 2002. High-Density Fiber-Optic Genosensor Microsphere Array Capable of Zeptomole Detection Limits. Analytical Chemistry 74(8):1836-1840; Walt, D. R. 2000. Molecular Biology: Bead- based Fiber-Optic Arrays. Science 287(5452):451-452. 10â White, B. J., and H. J. Harmon. 2005. Enzyme-Based Detection of Sarin (GB) Using Planar Waveguide Absorbance Spectroscopy. Sensor Letters 3(1-4):36-41; White, B. J., J. A. Legako, and H. J. Harmon. 2003. Extended Lifetime of Reagentless Detector for Multiple Inhibitors of Acetylcholinesterase. Biosensors and Bioelectronics 18(5-6):729-734; Legako, J. A., B. J. White, and H. J. Harmon. 2003. Detection of Cyanide Using Immobilized Porphyrin and Myoglobin Surfaces. Sensors and Actuators, B: Chemical 91(1-3):128-132; White, B. J., J. A. Legako, and H .J. Harmon. 2003. Spectrophotometric Detection of Cholinesterase Inhibitors with an Integrated Acetyl-/Butyrylcholinesterase Surface Sensors and Actuators, B: Chemical 89(1-2):107-111.
70 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Surface Acoustic Wave (SAW) Sensors SAW sensors are a mature technology first described in the 1970s.11 Many advances in this technology have been made since then.12 SAW chem- ical sensors are based on the change in the propagation of an acoustic wave over a piezoelectric substrate treated with a polymer coating. The polymer coatings or films are selected so that each will have a different chemical affinity for CWAs and TICs. In operation, SAW sensors are typically used in conjunction with a sample preconcentrator. Key characteristics of SAW technology based on the cited references are presented below. Dynamic Range and Detection Limit: The dynamic range of a typical SAW chemical sensor is 5-6 orders of magnitude, measuring from about 1 pg to 1 Î¼g of vapor. However, it depends on the vapor being measured. Nerve agents, such as GB, can usually be detected at less than 1 mg/m3, whereas the detection limit for HD is about 1-2 mg/m3. Response Time: The time for the sensor to respond to mass changes in the selective polymer coating is usually less than 1 ms. In typical vapor-sensing applications, however, it is more likely that the response time will be de- termined by the time needed for the preconcentrator to obtain the sample, then for the vapor to be transported to the polymer-coating surface and for equilibrium to be established. The true response time could be greater than 10 s (with currently available systems). False-Positive Readings: SAW devices are effective and reliable for detec- tion of very small amounts of CWAs, such as GB and HD. SAW devices are typically not subject to false alarms due to the presence of other compounds in the sample stream. A preliminary separations stage and careful experi- mental procedure design should minimize the risk of false positives due to garment off-gassing or residual decontamination chemicals. If designed properly, a SAW detector can be used to detect CWAs effectively in a variety of environmental conditions. Response Over Temperatures and Humidities: Although the polymer coat- ings used in SAW sensors can change physically when the devices are ex- posed to conditions outside the operating-temperature range, testing has 11â H. Wohltjen, and R. Dessy. 1979. Surface Acoustic Wave Probe for Chemical Analysis I. Introduction and Instrument Design. Analytical Chemistry 51(9):1458-1475. 12â See the following reviews for more information: Grate, J. W. 2000. Acoustic Wave Mi- crosensor Arrays for Vapor Sensing. Chemical Reviews 10(7):2627-2648; Smith, J. P., and V. Hinson-Smith. 2006. Product Review: The New Era of SAW Devices. Analytical Chemistry, June 1, pp. 3505-3507.
DESIGN CHALLENGE: MANNEQUIN UNDER-ENSEMBLE SENSING 71 confirmed that SAW sensors can maintain their accuracy in temperatures of 14-104oF. The various polymer coatings used in the SAW devices have various sensitivities to humidity, so a concentrator can be incorporated into the design to permit moisture to bypass the detectors while vapors of interest are analyzed. Design Challenges and How They May be Addressed Although the technologies cited above have the ability to detect CWAs, meeting most of or all the requirements cited in Tables 3.5 through 3.7, several design challenges are related to their adaptation or incorporation into the PETMAN system. Those challenges are categorized as associated with optimization or tailoring of the basic sensing technologies for this ap- plication or with incorporation into a mobile PETMAN mannequin. The challenges are discussed below. Challenges Associated with Validation and Optimization for the PETMAN System The sensor systems that need to be validated and optimized for use in the PETMAN system have several aspects, such as size, time response, ârecovery time,â and hysteresis. Size (âFootprintâ and Profile): Obviously, some sensor technologies have a smaller footprint and profile than others. The âfootprintâ and thickness or volume should be minimized so that they do not interfere with the op- eration of the PETMAN or the ânaturalâ movement of the garment. The PAD sampler is 1.5 Ã 1.25 Ã 1/8 inches. Current SAW devices are 3.5 Ã 2 Ã 1.2 inches and chemicapacitor devices are about 2.5 Ã 1.5 Ã 0.5 inches. However, the sensing component in these devices is only a fraction of the size, so it may be possible to separate the location where the analyte-coating interaction occurs (the sensor) from the electronics that power the unit to minimize the size of the devices. Fiber-optic sensors are likely to be much smaller and may be easier to incorporate into the PETMAN system. Effects of Humidity: Testing is needed to ensure that the detector is not af- fected by condensed moisture (for example, associated with perspiration). Time of Response: It is estimated that SAW sensors can make readings every 10 s or more. That meets the threshold requirement (T), but ad- ditional SAW sensor development may be required if the stated objective (O) of a reading every 1 s is to be achieved. The chemicapacitor and fiber- optics-based sensors are expected to have response times of 1 s or less. If a
72 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT preconcentrator or an initial separation stage is required, this time required for analysis could increase. Effects of Temperature: The SAW sensor will provide an accurate estimate of the amount of agent present over a temperature range of 14-104oF. Test- ing will have to be performed to determine the influence of temperature on the performance of the fiber-optics-based and chemicapacitor sensors. If the stated PETMAN objective requirement of 125oF is to be achieved, a major R&D effort for sensor-coatings could be necessary. Reversible Response of Sensors: Developers of chemicapacitor and SAW de- tection technologies have stated that their technologies are reversible, that is, the sensing units will detect a drop in the concentration of CWAs. But some fiber-optics-based detection systems may not be able to detect a drop in the concentration of agent (after exposure to a higher concentration), and further development may be necessary to overcome that deficiency. Hysteresis: Additional testing will be necessary to assess how many times the coatings of the various sensors can be used. Alternatively, it may be more feasible simply to replace âcoated componentâ parts, such as those used with the fiber-optics-based systems, after each test. Challenges Associated with Incorporation into the PETMAN A number of design considerations are related to physical incorporation of detection technology into the PETMAN system, for example, mounting, location, robustness, and power source. Mounting of Sensor on PETMAN: It will be a challenge to provide an unobtrusive package that can be mounted at multiple points (50 or more locations) on the mannequin body. The fiber-optics-based sensors appear to be small enough to be mounted in a nearly flush package (less than 0.1 inch high) or possibly woven in a manner similar to the Georgia Institute of Technology adaptive and responsive textile structure (ARTS) fabric system. (See Chapter 5 for a description of this technology.) If SAW or chemicapacitor technology is used, however, the mannequin may require recessed areas to accommodate and minimize the profile of the individual sensing devices. Resistance to Shock and Vibration: To ensure that a sensorâs response is not affected by exposure to shock and vibration, it may be necessary to envelop it in an inert damping polymeric material, such as silicone sponge.
DESIGN CHALLENGE: MANNEQUIN UNDER-ENSEMBLE SENSING 73 If so, damping should not interfere with agent flow to the sensor or with the sensorâs response to the agent. Powering (Wireless vs Hard Wiring or Tethering of Sensing Units): Multiple options are available for powering the sensor technology. For example, if internal wiring can be made available, a socket capable of receiving a standard dual-in-line package (DIP) could be built into the skin of the mannequin and even recessed to allow a flush surface. The wires under the skin could connect to a readout circuit elsewhere on the body and thereby connect to a wireless interface.The sensor chip could be tethered to the readout circuit via a flexible printed-circuit cable (also called laminated flat flexible cables). The sensor package would be less than 0.1 inch high, and the circuit board could be in a part of the mannequin where it would not interfere with movement. Flexible wiring (less than 0.04 in. thick) would connect to a readout circuit elsewhere on the body and thereby connect to a wireless interface. Protection from Condensed Moisture or Perspiration: It may be necessary to protect (by design or positioning) the sensors from direct exposure to or contact with condensed water associated with perspiration. Again, interfer- ence with agent flow or sensor response must be ensured. Airflow Across Sensing Units: Sampling analysis may require that air con- taining an analyte be pulled into and across a sensorâs interaction surface. For example, a fiber-optics-based system may passively absorb and detect the presence of an agent, whereas a SAW or chemicapacitor sensor may require a sample to be pulled into its detection system. If the latter is the required, provisions must be made for creating airflow. Decontamination or Replacement of Sensors: If it is necessary to decon- taminate or replace a sensor or sensor component after each test, provisions must be made for easy access. Signal Interference: If the system is wireless, it must be ensured that trans- mitted signals from other components of the PETMAN do not interfere with sensor signals. Cost-Benefit Analysis and Trade-offs The chemicapacitor, fiber-optics-based, and SAW technologies have the potential to meet the cited requirements for the detection of CWA penetra- tion in the PETMAN system. It is likely that all the sensor technologies will require additional validation, optimization, and modification.
74 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT The hurdles faced by organizations in developing and commercializing a new sensor can be formidable (Table 3.7). For example, although SAW and chemicapacitor technologies have matured to the point where commer- cially available detection systems are available, their current footprints and profiles may have to be reduced to be practical for PETMAN application. Although preliminary testing of fiber-optics-based technology suggests that it has great potential for this application, additional laboratory validation and modification for successful incorporation into the PETMAN system will be necessary. It is difficult to accurately estimate the costs associated with the devel- opment and optimization of technologies for the PETMAN application. However, the cost to equip a PETMAN with a fiber-optics-based system (a finished product, excluding development and optimization costs) should be relative low, possibly less than $5,000.13 If a SAW or chemicapacitor system is used, the product cost after development could exceed $10,000.14 Feasibility and Potential Alternatives When assessing the feasibility of a given technology, the following were considered: â¢ Availability and reliability of the technology â¢ Ability to meet the PETMAN requirements, outlined in Tables 3.5 through 3.7 â¢ Likelihood of overcoming the design challenges associated with the adaptation of the technology and its incorporation into the PET- MAN system â¢ Time to develop and optimize â¢ Cost â¢ Maintenance The three example technologies discussedâchemicapacitor, fiber-op- tics-based, and SAWâhave the potential to meet the cited requirements for the detection of CWA penetration or permeation in the PETMAN. How- ever, further study, optimization, and design challenges must be addressed before any of those technologies can be effectively used in the PETMAN mannequin application. Alternatively, the PADs currently used in the MIST system for the cumulative detection of methyl salicylate may be adapted for this appli- 13â Based on presentations by Harmon and Walt in Appendix D. 14â Based on currently available chemical sensor systems from Mine Safety Appliances, Sea- coast Science, and others.
DESIGN CHALLENGE: MANNEQUIN UNDER-ENSEMBLE SENSING 75 TABLE 3.7 Commercialization of a New Sensor Estimated Estimated Time to Complete Investment Phase (months) ($ millions) Milestone 1 12-36 â Laboratory prototype 2 4-6 0.3-0.5 Development and commercialization plan 3 6-10 0.5 -1 Final design 4 6-10 0.5-1 Manufacturing prototype 5 4-6 0.5-1 First production run 6 2-4 0.2-0.5 Market release Total 22-36 2-4 SOURCE: Taylor, R. F., and J. S. Schultz, eds. 1996. Handbook of Chemical and Biological Sensors, Institute of Physics Publishing, Philadelphia, Table 23.9, p. 573. cation. Although it is low in cost and could be adapted for the detection of CWAs, the desired advances associated with the PETMAN applica- tionâsuch as detection of penetration or permeation of the garment in 1-s incrementsâwould not be realized. On the basis of consideration of the material presented, the following conclusions were made: Conclusion 3-1: Both the PADs currently used and the real-time sen- sors identified have the potential to achieve the PETMAN threshold requirements. The real-time sensors identified also have the potential to achieve the objective requirements of PETMAN. However, several design challenges exist for adapting or incorporating any of these sam- pling systems into the PETMAN. These challenges include: â¢ Mounting of the sensor onto the mannequin â¢ Resistance to shock and vibration â¢ Powering of the sensor units (wireless versus hard wiring or tether- ing of sensing units): â¢ Protection from condensed moisture (perspiration) â¢ Airflow across the sensing units â¢ Decontamination and/or replacement of the sensors â¢ Signal Interference Recommendation 3-1: The existing set of PETMAN performance re- quirements and the additional criteria identified and described in this chapter should be used for the selection and evaluation of sensors for the PETMAN system.
76 SOLDIER PROTECTIVE CLOTHING AND EQUIPMENT Conclusion 3-2: If the PETMAN must operate in the environmental chamber at 125oF (an objective level requirement), a major R&D effort for sensor-coatings could be necessary. Conclusion 3-3: The hurdles faced by organizations in developing and commercializing a new sensor can be formidable. The cost associ- ated with the development and optimization of technologies for the PETMAN application could be millions of dollars, and the product cost after development could range anywhere from a few thousand dollars to more than $10,000.