Chemical Warfare Agents Analyzer Based on Low Cost, Room Temperature, and Infrared Microbolometer Smart Sensors

Advanced IR emitters and sensors are under development for high detection probability, low false alarm rate, and identification capability of toxic gases. One of the most reliable techniques to identify the gas species is absorption spectroscopy, especially in the medium infrared spectral range, where most of existing toxic compounds exhibit their strongest rotovibrational absorption bands. Following the results obtained from simulations and analysis of expected absorption spectra, a compact nondispersive infrared multispectral system has been designed and developed for security applications. It utilizes a few square millimeters thermal source, a novel design multipass cell, and a smart architecture microbolometric sensor array coupled to a linear variable spectral filter to perform toxic gases detection and identification. This is done by means of differential absorption spectroscopic measurements in the spectral range of the midinfrared. Experimental tests for sensitivity and selectivity have been done with various chemical agents (CAs) gases and a multiplicity of vapour organic compounds (VOCs). Detection capability down to ppm has been demonstrated. 1. Introduction One of the most reliable techniques to identify the gas species is absorption spectroscopy in the medium infrared spectral range, where most of existing toxic compounds exhibit their strongest rotovibrational absorption bands [1, 2]. The present work will describe a compact point sensor for providing early warning in the presence of CAs in the air. Battlefields and urban areas at risk of terroristic attack were the foreseen application scenarios. Wide chemical range and effective identification of targets and rejection of other vapours were given as the key performance objectives. The sensor is based on Active Multispectral Infrared Absorption Spectroscopy in the gas phase and uses 38 spectral channels to represent molecular fingerprints across the LongWave IR spectrum (LWIR). The heart of the sensor is an advanced detector device that integrates microbolometers, optical filter arrays, and front-end electronics on silicon chip. 2. Sensor System The sensor system essentially consists of an IR thermal source, a multipass optical cell, and an array of detectors and filters, plus electronics and software for signal read-out, processing and analysis. Figure 1 shows a scheme of the sensor system. A description of the early design of the sensor system has been reported in [3]. Figure 1: Scheme of the sensor system. The IR radiation emitted by the source is first modulated by a mechanical