Compact step-added T-type PAC for enhanced hydrogen detection: A photoacoustic frequency shift approach

In this study, we introduce an innovative photoacoustic frequency shift (PAFS) technique for hydrogen (H₂) detection, complemented by both theoretical models and practical experiments. To mitigate cross-sensitivity, we analyzed the sound speeds of six different gases, confirming minimal interference with H₂ due to significant velocity disparities. Central to our approach is the design of a miniaturized step-added T-type Photoacoustic Cell (PAC), with parameters meticulously optimized for enhanced performance. Using COMSOL Multiphysics' Thermal Viscous Acoustics module, we conducted simulations to evaluate the quality factor and acoustic pressure, both crucial for the sensor's efficiency. Additionally, we assessed the system's stability, influenced by gas flow, through gas velocity distribution analyses using the Computational Fluid Dynamics module. Experimental investigations focused on the system's sensing performance, revealing a distinct frequency shift of ∼45 Hz for every 1 % change in H₂ concentration, with a high linear correlation (R² = 0.99825). The system's response and recovery times were measured at 1.09 s and 1.25 s, respectively. Long-term stability, evaluated over 3000 s using Allan deviation, indicated a minimum detection limit (MDL) of 102.47 ppm at an integration time of 375 s. These findings validate the efficacy of the step-added T-type PAC in H₂ detection.