Highly Sensitive Photoacoustic NO2 Measurement System Based on an Optimized Ring-Shaped Resonant Cell

This work proposes the feasibility of an ultraviolet (UV) photoacoustic (PA) gas sensing system based on an innovative resonant PA cell structure. The system design exploits the resonant characteristics of a ring-shaped cell whose design has been optimized through analytical and finite element method (FEM) analysis to meet the requirements of the target application. In particular, the device characteristics in terms of size, frequency response, limit of detection (LOD), and related metrological characteristics were taken into account. The overall designed sensing system is made up of low-cost and commercially available components and it represents a scalable solution for monitoring different gas species. The performance of the sensing system toward NO2 was experimentally assessed, showing a relative sensitivity of 0.38%/ppm NO2 and a LOD of 500 ppb with response and recovery times in the order of a few seconds. Moreover, the cross-sensitivity of the PA sensor toward CO, CH4, and NH3 was evaluated.