Single Fiber-Type Double Cavity Enhanced Photoacoustic Spectroscopy Sensor for Trace Methane Sensing

In this paper, a novel single fiber-type double cavity enhanced photoacoustic spectroscopy (SFDCE-PAS) sensor has been proposed and demonstrated for trace methane (CH ₄ ) sensing. The sensor mainly consists of a Fabry-Perot (F-P) chamber, a fiber-optic ceramic pin, a polyethylene terephthalate (PET) film, and a photoacoustic (PA) cavity. The PET film acts as an acoustic sensing unit and the excitation light can transmit into the PA cavity through this PET film to increase the gas absorption range. The performance of the SFDCE-PAS sensor has been carefully evaluated in comparison with a single fiber-type photoacoustic spectroscopy (SF-PAS) sensor with one cavity in a PAS system for CH ₄ sensing. It has been found out that the PA signal detected by the proposed SFDCE-PAS sensor is about 6.2 times higher than the one of the SF-PAS sensor, demonstrating superior sensitivity with a compact architecture. The proposed sensor is suitable for long-distance in-situ real-time measurement of trace CH ₄ gas in harsh environments with narrow space such as coal mines, due to its unique architecture with a single fiber and dual cavities.