[The principle and technical analysis of methane detection using infrared absorption spectroscopy].

There has been considerable interest recently in methane sensor based on infrared absorption spectroscopy for industrial detection and environment monitoring. The present paper presents the intensites of methane mid-infrared fundamental absorption bands, near-infrared combination band of v2 + 2v3 and overtone band of 2v3, and it was found that the absorption strengths of fundamental bands are two orders of magnitude higher than those of overtone bands and three orders of magnitude higher than those of the combinations. Theoretically, mid-infrared detection system is much better. However, because the near-infrared source and detector are more maturely developed and cheaper, near-infrared technology is widely used. Furthermore, the near-infrared radiation can be transmitted through ordinary low-loss silica fiber, suitable for long-distance methane sensing system, meeting the needs of industrial mining and other aspects. But with the development of mid-infrared detector and high-power high-sensitivity devices, low priced micro sensor modules will be more and more developed. The development of optical methane sensors is reported in this paper. Several detection technologies were investigated such as differential absorption, harmonic detection, cavity spectroscopy enhancement and photoacoustic spectroscopy. The theoretical formula, sensitivity and system structure of these technologies are presented.