System and method for high sensitivity optical detection of gases

Abstract

A method and apparatus architecture for detecting gases, particularly hazardous gases which should be detected in miniscule amounts. High sensitivity detection of chemical warfare agents (CWAs) is set forth with very low probability of false positives (PFP) by the use of an innovative laser-photoacoustic spectrometer (L-PAS). Detection of diisopropyl methylphosphonate (DIMP), a decomposition product of Sarin and a relatively harmless surrogate for the nerve gases, is made in the presence of other gases that are expected to be interferences in an urban setting. Detection sensitivity for DIMP in the presence of these interferences of better than 0.45 ppb, which satisfies current homeland and military security requirements is shown as well as the first analysis of optical techniques for the detection of chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) in real world conditions.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This patent application is related to and claims priority from U.S. Provisional Patent Application Ser. No. 60 / 621,099 filed Oct. 22, 2004 entitled GAS DETECTOR (aka SYSTEM AND METHOD FOR HIGH SENSITIVITY OPTICAL DETECTION OF GASES) which application is incorporated herein by this reference thereto.COPYRIGHT AUTHORIZATION [0002] Portions of the disclosure of this patent document may contain material which is subject to copyright and / or mask work protection. The copyright and / or mask work owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright and / or mask work rights whatsoever. BACKGROUND OF THE INVENTION [0003] 1. Field of the Invention [0004] This invention relates to the detection of hazardous and / or toxic gases, including warfare gases, and more particularly to a metho...

AI Technical Summary

Benefits of technology

[0027] The simulation model developed to evaluate the sensor performance, includes a model of realistically contaminated air, a model of actual sensor performance, and quantitative spectral libraries. The results of an L-PAS sensor performance simulation for CWA detection are set forth with the analysis extended to predict performance of notional sensors with different operational characteristics and different levels of air contamination, thus, providing “scaling laws” for optical sensors and permitting sensor performance evaluations in extreme situations.

[0031] In one embodiment, a gas detector has an optical analyzer detecting in a sample of gas optical absorbance of the sample at a plurality of wavelengths. The optical analyzer then transmits an absorbancy signal representative of optical absorbancy for each respective one of the plurality of wavelengths. A spectral library of gas species absorbing one or more of the plurality of wavelengths is provided that includes determined absorptions for expected gases and target gases. In conjunction with this library, a processor receives the absorbancy signals from the optical analyzer and applies pattern recognition (such as least squares fitting) using the absorbancy signals and the determined absorptions to provide mole fraction quantities for each of the expected gases and each of the target gases. In this way, the sample of gas may be analyzed for presence and quantity of expected gases and target gases.

[0032] In another embodiment, a high sensitivity gas detector for detection of hazardous gases with reduced probability of false positive and false negative signals uses a light source transmitting modulated tunable radiation to illuminate a photoacoustic test cell. The photoacoustic test cell has a microphone system that transmits a photoacoustic signal to a signal receiver that receives the microphone signal. The signal receiver transmits a normalized signal to a signal processor which analyzes the normalized signal in conjunction with at least one entry in a library for signal signatures for gases detectable by the radiation. The signal processor transmits a resulting signal indicating a quantity of the hazardous gases in the test cell. In this way, detection of known hazardous gases can be made by illuminating sample air or other gas in the photoacoustic test cell.

Problems solved by technology

Problems arise in the detecting of a target species in the presence of a multitude of interferences that are often are stochastic.

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