An Airflow Volumetric Flowmeter Using ScAlN-Based Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) in Small-Diameter Pipelines

This paper presents an airflow volumetric flowmeter utilizing ScAIN-based piezoelectric micromachined ultrasonic transducers (PMUTs) for application in small-diameter pipelines. The device contains two pieces of 4×4 PMUTs arrays with resonant frequency of 171 kHz. The dimension of the PMUTs array is about 4×4 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, allowing it to measure gas flow in a pipeline with an inner diameter of 6 mm. By applying voltage excitation, the downstream and upstream waveform signals from PMUTs are processed through cross-correlation and interpolation to determine the time difference of ultrasonic wave propagation in the gas. The flowmeter maintains a relative error within 3% across a reference volumetric flow range of 2–800 L/H. The results indicate potential application of PMUTs for accurately measuring gas flow in small-diameter pipelines.