Highly-sensitive photoacoustic gas sensor with dual resonant modalities for simultaneous NO and NO2 detection

Photoacoustic spectroscopy (PAS) gas sensors based on acoustic resonators have high detection sensitivity and are widely used for trace gas detection. However, there are challenges such as difficult time/frequency separation, low signal-to-noise ratio of higher-order modes, and high sample consumption in multi-gas detection. Here, we present a dual-modality PAS (DM-PAS) gas sensor for simultaneous detection of NOx. The sensor incorporates two integrating spheres and a cylindrical tube to excite both Helmholtz and longitudinal resonances within a single cell. LED and QCL light sources are modulated to generate PA signals originated from the dual resonant modalities, which are detected by the array of MEMS microphones. Allan deviation analysis shows a minimum detection limit (MDL) of 61.5 ppb for nitrogen dioxide (NO2) and 2.0 ppb for nitric oxide (NO) at over 450 s integration time. Furthermore, experimental results demonstrate the favorable repeatability and response performance of this sensor. The proposed sensor configuration provides a novel approach to realize the simultaneous detection of multiple gases.