Design of a novel gas sensor structure based on mid-infrared absorption spectrum

A new type of light-collecting structure that can greatly improve signal-to-noise ratio for gas test was designed on the basis of mid-infrared absorption spectrum principle. A rotational symmetric ellipsoid reflector was employed to collect the mid-infrared radiation with the light source and detector on two focuses, and Beer–Lambert law was applied to construct related math models. Theoretical analysis showed that this structure could perfectly enhance the gains of signals by 648 times. Experimental analysis of methane gas was carried out by using principle of differential absorption, 3.31 μm mid-infrared absorption wavelength and double PbSe detectors. The detection limit of this system was 50 ppm and the test precision was as high as 3%. Due to the attenuation and imprecise ellipsoid reflector, the experimental gain of differential signal was 220 times.