Characterization of micro-scale gas leaks using an optomechanical ultrasound sensor

We used an optomechanical microphone to measure the acoustic signals emitted by compressed-air jets emanating from apertures as small as ∼5 μm. In keeping with the predictions of aeroacoustic theory, spectra extending into the high-frequency (MHz) ultrasound region were observed. Most of this acoustic energy lies well above the range of a conventional ultrasonic microphone. Conversely, the broadband response of the optomechanical sensor offers the potential to localize and quantify leaks based on a more complete knowledge of the acoustic spectrum. We show that the minimum detectable flow rate, set by the onset of turbulence, scales with the hole size and was as low as ∼10-3 Pa·m3·s-1 for the smallest holes studied here. The results demonstrate that a sufficiently broadband and sensitive microphone might enhance the utility of "acoustic sniffer" tools for quantitative gas leak detection.