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 2<i>f</i> 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.