Photoacoustic Spectroscopy Gas Sensor Based on a Novel π-Type Helmholtz Photoacoustic Cell

This paper presents a photoacoustic spectroscopy (PAS) gas sensor based on a novel π-type Helmholtz photoacoustic cell (πH-PAC) for the first time. The acoustic properties of the πH-PAC were investigated using finite element analysis. The πH-PAC not only enhances the photoacoustic signal by increasing the interaction path between the light source and PAC, but also positions the light source away from the condenser microphone detection point, thereby reducing coherent noise generated by interactions with the window plate during laser incidence. Two distinct excitation methods were designed based on its structure. Compared to the traditional T-type PAC of identical dimensions, the photoacoustic signal was amplified by a factor of 24.76. The πH-PAC based PAS gas sensor exhibited excellent linear concentration response. Allan deviation analysis indicated that the minimum detection limit (MDL) of the πH-PAC-based PAS gas sensor for methane (CH₄) detection could be enhanced to 328 ppb when the system average time was set to 1000 s.