High Resolution and Large Range Ultrasonic Flow Monitoring Based on Monolithic PMUT Phased Array with Bidirectional Beams

Traditional ultrasonic flowmeters based on transit time consist of two identical transducers arranged at the opposite sides of a straight pipe, with both of them operating as transmitter (TX) and receiver (RX) to obtain the volume flow rate, which is proportional to the difference between the downstream and upstream ultrasound transmitting time (delta-Time-of-Flight,ΔToF). This sensing scheme usually has difficulties in increasing the ultrasound's propagation path for a sufficient ΔToF resolution, and lacks adaptation to various pipe geometries. This paper demonstrates flow monitoring tailored for zigzag-shaped pipes with 150 mm ultrasound propagation path via a compact 3.6 mm x 3.6 mm piezoelectric micromachined ultrasonic transducer (PMUT) phased array. Through optimized device design and sequential control, the monolithic five-channel PMUT array can generate symmetric V-shaped acoustic bidirectional beams matching well with zigzag pipes, significantly promoting the adaptation and universality of ultrasonic flow sensing. The proposed methodology enables large range (0.5-35 L/min, airflow) flow metering with good linearity (Adjusted R-Square is 0.99706) and high resolution (185 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\displaystyle \text{ns}/\mathrm{L}\cdot\min{}^{-1}$</tex>, or 2032 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{ns}/\mathrm{m}\cdot \mathrm{s}^{-1}$</tex>).