Performance enhancement of a mid-infrared CH4 detection sensor by optimizing an asymmetric ellipsoid gas-cell and reducing voltage-fluctuation: Theory, design and experiment

A mid-infrared (MIR) CH4 sensor was experimentally demonstrated by employing an asymmetric ellipsoid multi-pass gas-cell. Novel theory and formulas were proposed for optimizing the gas-cell structure, and both hardware and algorithm were designed to determine the accurate characteristics by reducing effect of reference voltage-fluctuation of analog-to-digital converter (ADC). The CH4 sensor was fabricated and experiments were carried out to obtain its performance. The absolute detection error is less than 5%. The minimum detection level (MDL) and the detection sensitivity are determined to be about 5 and 6-7 ppm, respectively, under the low concentration of less than 1000 ppm. The response time is measured to be within the range of 5-6 s, and the Allan variation plot shows that the system possesses acceptable stability over long term operation. Compared to our two previous reported detection devices with symmetric ellipsoid gas-cell and without reducing voltage-fluctuation, this sensor exhibits enhanced performances including higher detection sensitivity, lower MDL and shorter response time. (C) 2011 Elsevier By. All rights reserved.