Mems-based spectrophotometric system

Abstract

A portable spectrophotometric system for detecting one or more target substances. In a representative embodiment, a system of the invention has an optical grating, an array of photo-detectors, and a MEMS device having a movable plate positioned between the grating and the array. Light transmitted through a gaseous sample is dispersed by the grating and is imaged onto the movable plate, which has a plurality of openings corresponding to selected infrared absorption lines of the target substance. A small-amplitude oscillation is imparted onto the plate such that the openings periodically move in and out of alignment with the corresponding intensity features in the image, which modulates electrical signals generated by the corresponding photo-detectors. A lock-in signal processor analyzes the modulation pattern by comparing it to the pattern expected in the presence of the target substance. When a positive correlation between the patterns is established, the system warns the user about the presence of the target substance.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to sensors and, more specifically, to optical gas detectors. 2. Description of the Related Art Gas analyzers are used in environmental monitoring, industrial process control, geologic exploration, and medical, analytical, and military applications. For example, gases such as hydrogen sulfide and sulfur dioxide accompany natural gas and are often present in industrial environments. Since exposure to these gases is a health hazard, low concentrations, typically in the range of parts per million (ppm), need to be detected. Different analytical techniques such as optical spectroscopy, mass spectrometry, gas chromatography, electrochemical analysis, etc., may be used for detection of substances present in relatively low concentrations. One particular technique, optical spectrophotometry, is based on the absorption of electromagnetic radiation by the sample in a selected spectral range and is generall...

AI Technical Summary

Benefits of technology

Problems in the prior art are addressed, in accordance with the principles of the present invention, by a portable spectrophotometric system for detecting one or more target substances. In a representative embodiment, a system of the invention has an optical grating, an array of photo-detectors, and a MEMS device having a movable plate positioned between the grating and the array. Light transmitted through a gaseous sample is dispersed by the grating and is imaged onto the movable plate, which has a plurality of openings corresponding to selected absorption lines of the target substance. A small-amplitude oscillation is imparted onto the plate such that the openings periodically move in and out of alignment with the corresponding intensity features in the image, which modulates electrical signals generated by the corresponding photo-detectors. A lock-in signal processor analyzes the modulation pattern by comparing it to the pattern expected in the presence of the target substance. When a positive correlation between the patterns is established, the system warns the user about the presence of the target substance.

Problems solved by technology

Since exposure to these gases is a health hazard, low concentrations, typically in the range of parts per million (ppm), need to be detected.

However, one problem with prior-art spectrophotometric systems is that they are relatively difficult to adapt for portable, particularly hand-held, applications.

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