A single-chip flow sensor based on bimorph PMUTs with differential readout capabilities

This work reports the measurements of air flows for both magnitude and direction based on piezoelectric micromachined ultrasonic transducers (PMUTs) for the first time. The sensor operates in the pulse-echo mode to detect changes in flow with a measured sensitivity that is 286% of that for previously reported MUT-based flow meters, all without commanding any voltage over 5V. The enhancement is a result of four unique features reported herein: (1) the high-sensitivity bimorph structure of the fabricated PMUTs; (2) the spatial separation between the transmitter (Tx) and receiver (Rx) transducer elements; (3) the high directivity of the transmitted acoustic pulse; and (4) the differential readout. Owing to the single-chip design, our flow sensor is the first of its kind capable of measuring flow direction in addition to speed with high sensitivity.