Chemical sensors, explosive detection

This chapter provides an overview of the basic principles and designs of such sensors. A chemical sensor to detect trace explosives and a broadband fiber optic electric-field sensor are presented as practical examples. The polymers used for the trace explosive sensor are unpoled and have chromophores randomly orientated in the polymer hosts. The electric field sensor uses a poled polymer with chromophores preferentially aligned through electrical poling, and the microring resonator is directly coupled to the core of optical fiber. 

Trace portals could also be used for bulk detection because of the likelihood that a mass of explosive concealed on the person would present an adequate chemical signature. The combination of a trace and anomaly portal would provide a powerful multi-sensor platform that would offset the limitations of the individual technologies. Currently, a commercially available multi-sensor explosives detection personnel portal that combines trace and anomaly methods does not exist. 

Develop robust and reliable sensors for detection of chemical agents, biological agents, radioactive materials, and explosives. 

During World War II, copious quantities of ordnance were lost into the harbor at Halifax, Nova Scotia. Decades later, these UUXO now present a significant environmental contamination problem. Studies conducted on this ordnance by Sandia National Laboratories [1] suggest that there may be sufficient concentrations of explosive chemical signature compounds emanating from UUXO to enable detection with chemical sensors. Some UUXO in Halifax Harbor have been shown to produce parts-per-billion levels of explosives in the water near the ordnance. In addition to the parent explosive compound (TNT), other explosive-related compounds such as 2,4-dinitrotoluene (2,4-DNT) were detected, as were degradation products of TNT such as 4-amino-2,6-dinitrotoluene (4-ADNT), and... 

In another study, Darrach et al. [2] reported that samples collected near intact UUXO targets contained traces of explosives at up to parts per billion (ppb) concentration levels. The samples were analyzed in the laboratory, using solid-phase microextraction (SPME) to extract target analytes from the samples. The samples were then processed using a reversal electron attachment detection (READ) technique. If the levels of contamination found in these studies are representative of that emanating from most UUXO, the implication is that sensitive chemical sensors such as the SeaDog may be useful for detecting UUXO. 

The Fido technology is currently under evaluation for use by U.S. military forces. The Fido X and Fido XT are available as commercial off-the-shelf (COTS) items. Consequently, the technology is adequately mature for commercial deployment. However, as a platform technology, the AFP sensor and Fido detection system support broad application to meet explosives detection needs. Further, Nomadics has incorporated the amplification features of AFP into other sensor mechanisms aimed at the detection of analytes that are not explosives related, including other chemicals and compounds of interest in the biomedical and food safety fields. Thus, while the technology is mature enough for commercialization, its potential is far from fully exploited. 

As mentioned earlier, chemicals and explosives are usually detected spectroscopically. Fiber-optic-based chemical sensors have application in the real-time tracking of rapidly changing chemical environments. These sensors provide rapid... 

There is a growing need to sense molecules for applications as diverse as waste management, explosives detection, and disease prevention. Goals of chemical sensor development are to create devices that require little power and that are robust, sensitive, selective, fast, compact, and inexpensive. In this chapter, we describe optical techniques based on semiconductor luminescence that are promising methods for chemical sensing applications. 

C. Gumming, Amplifying fluorescent pol mier arrays for chemical explosives detection, in Electronic Noses and Sensors for the Detection of Explosives, (eds JW Gardner and J Yinon), NATO ASI Series, Kluwer Academic Publishers, Dordrecht, 2004. 

The problem of explosives detection has not been a typical domain of electronic nose research, mainly since it requires extreme sensitivity to specific chemical compounds (usually a small number) which often occur in trace amounts below the detection limit of available sensors. However, as new and more sensitive technologies for chemical sensor instrumentation are discovered, we should consider how these can be exploited individually and... 

An example of one of TSA/TSL s R D funded MEMS based project is the Sandia National Laboratories (SNL) MicroHound project. This is based on the SNL Micro Chem Lab on a Chip , illustrated in Figure 1. The original prototype system from SNL was developed for high vapour pressure, chemical weapons (CW) detection, which utilized a MEMS GC separator, with miniature surface acoustic wave (SAW s) based sensors. The system included an inlet, coated pre-concentrators, detectors, and pumps. To make this useful for trace explosives detection, the addition of an alternate front-end sample collection/macro-preconcentrator and MEMS based coated-preconcentrator is necessary, along with the option to utilize or exclude the MEMS GC separator followed by detection by either, or both, SAW s and miniaturized IMS detectors. 

This book examines both the potential application of electronic nose technology, and the current state of development of chemical sensors for the detection of vapours from explosives, such as those used in landmines. The two fields have developed, somewhat in parallel, over the past decade and so one of the purposes of this workshop, on which the book is based, was to bring together scientists from the two fields in order to challenge the two communities and, mutually, stimulate both fields. 

There are a myriad of applications for chemical sensors, and one important area is the detection of toxic gases and vapors. Toxic industrial chemicals and materials (referred to as TICs and TIMs) represent one class of materials for which chemical sensors are designed and applied. Chemical warfare agents (CWAs) are another set of materials for which chemical sensors are used, and they represent one of the most challenging groups of analytes due to their extreme toxicity, which translates to a very low required detection limit. Detection of explosives additionally requires high sensitivities due to the low vapor pressures of the explosive materials (order of magnitude 6 x 10-6 Torr for TNT and 5 x 10 9 Torr for RDX). 

Other devices such as the Cyrano Sciences, (Smiths Detection, Edgewood, MD), a handheld device using conductive polymer films deposited in an array on a ceramic substrate and the Micromachined Aconstic Chemical Sensor (Sandia National Laboratories, SNL), which is able to detect VOCs, explosives, illicit drngs, and chemical warfare agents, are also commercially available [32],... 

One approach to high-selectivity detection of explosives at ultratrace levels that may overcome the processing time limitation of immunosensors is to combine a chemical sensor tailored to specific target molecules with a molecular transducer thatresponds... 

Sensors to detect and identify explosives, narcotics, weapons, chemical agents, biohazards, and contraband... 

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