T-type differential Helmholtz photoacoustic cell with microphone array for simultaneous multi-gas monitoring at ppb level

Multi-gas detection plays an important role in the fields of industrial safety and environmental protection. Currently, achieving simultaneous and high-precision detection of multiple gases faces many challenges. To solve this problem, a T-type differential Helmholtz photoacoustic (PA) cell integrated with an 8-microphone array was developed. The specially designed T-type differential Helmholtz structure enables signal enhancement and noise suppression. Furthermore, through the signal superposition and differential effects among the eight-microphone symmetrical array, the signal-to-noise ratio (SNR) is improved by $\sim$3.64 times compared with the single-microphone configuration, achieving high-sensitivity gas detection at the ppb level. The developed sensor was used to simultaneously measure two typical gases (CH$_4$ and C$_2$H$_2$). Experimental results show that the sensor has excellent linearity, high stability, and remarkable sensitivity, achieving a limit of detection (LoD) of 402 ppb for CH$_4$ with a normalized noise equivalent absorption (NNEA) coefficient of 4.18$\times$10$^{-9}$ cm$^{-1}\cdot$W$\cdot$Hz$^{-1/2}$, and a LoD of 254 ppb for C$_2$H$_2$ with a NNEA coefficient of 1.52$\times$10$^{-9}$ cm$^{-1}$$\cdot$W$\cdot$Hz$^{-1/2}$. Therefore, this novel and compact gas measurement device is expected to play an important role in fields such as industrial safety monitoring and environmental pollution control.