A ppb-Level Chloroform Photoacoustic Gas Sensor Based on Omnidirectional Acoustic Sensing with a 3D Microphone Phased...

In recent years, the introduction of phased array technology into the field of photoacoustic spectroscopy gas detection has become a research hotspot, driving the breakthrough of photoacoustic signal acquisition from a single time-domain acquisition to spatial-domain acquisition. Current relevant studies are mostly limited to the scope of two-dimensional (2D) spatial acquisition, with innovations focusing on sensor types (such as micro-electro-mechanical systems microphone) and the transformation of photoacoustic cell (PAC) types (such as H-type PAC and Helmholtz PAC). However, the three-dimensional (3D) spatial acquisition of photoacoustic signals in PACs still faces technical challenges, and the spatiotemporal correlation of photoacoustic signals in 3D space remains unclear. In this study, a 3D microphone phased array was introduced into photoacoustic gas detection for the first time, proposing a 3D spatially enhanced photoacoustic sensing system based on omnidirectional acoustic detection. By embedding a spherical cavity at the center of an H-type PAC and symmetrically arranging six microphones along three orthogonal axes, effective acquisition of 3D spatial acoustic signals was achieved, and the coherence of photoacoustic signals in 3D space was verified. Experimental results demonstrated that the 3D six-microphone system achieved sensitivity enhancements by factors of 6 and 2 compared to one-dimensional and 2D microphone systems, respectively, and reduced the minimum detection limit by approximately 60.1% and 31.7%. This system ultimately achieves a ppb-level detection limit for chloroform (CHCl₃) gas. This study has for the first time realized the high-precision matching between the acquisition dimension of photoacoustic signals and their intrinsic dimension, thereby providing brand-new research ideas and technical implementation pathways for the design and development of spatial acquisition arrays in high-performance photoacoustic sensors.