Miniature Helmholtz photoacoustic sensor with high temporal resolution for trace gas detection

We propose a high-temporal-resolution photoacoustic sensor that operates on the beat frequency principle, incorporating a miniature Helmholtz photoacoustic cell (H-PAC) with a volume of 1.2 mL. The H-PAC comprises two identical acoustic channels configured in differential mode to suppress common-mode environmental noise. The performance of the sensor was characterized using trace acetylene (C₂H₂) as the target analyte. The results showed that the minimum detection limit (MDL) of C₂H₂ reached 536 ppb with an integration time of 185 s. The measured system gas exchange time was only 9.3 s at a flow rate of 100 sccm. In contrast to the traditional 2f demodulation scheme, the implemented rapid wavelength scanning approach acquires beat frequency signals every 20 ms, enabling the tracking of rapid concentration fluctuations with high temporal resolution.