Dual-Mode Multi-Microphone Enhanced Photoacoustic Gas Sensing System Using a Waveguide Ring Array

This study presents a waveguide ring-array photoacoustic cell (PAC) module, utilizing MEMS microphones as acoustic sensors and based on the multimicrophone signal enhancement principle, for trace gas detection via photoacoustic spectroscopy (PAS). The vibrational characteristics of the PAC, specifically its superimposed and self-differential operational modes, were first analyzed through simulations. The system's versatility and performance were then rigorously evaluated using two representative light sources─a distributed feedback (DFB) laser and a laser diode (LD)─with ammonia (NH₃) and nitrogen dioxide (NO₂) as the target gases. Employing the superimposed signal from eight microphones yielded a significant enhancement: the minimum detection limit (MDL) improved by 60-70%, the signal-to-noise ratio (SNR) increased nearly 3-fold, and sensitivity was boosted nearly 8-fold compared to using a single microphone. Remarkably, the system achieved MDL of 1.43 ppm for NH₃ and 33 ppb for NO₂. Furthermore, the self-differential mode demonstrated exceptional common-mode noise rejection capability. The developed module features a compact design, low fabrication cost, and outstanding analytical performance, offering substantial potential for optimizing existing commercial PAS systems.