Improved Ring-Down Time and Axial Resolutions of PMUTs via Phase-Shift Excitation Scheme

We have proposed a phase-shift cancellation scheme to reduce the ring down period of ultrasonic transducers and increase axial resolutions. A piezoelectric micromachined ultrasonic transducer (pMUT) consisting of 80 elements with circular diaphragms of 415 μm in radius made of 2 μm-thick AlN layer has a measured resonant frequency of 160 kHz. The ring down period is minimized by emitting ten pulses followed by six additional pulses with a 180° phase difference. Results show the ring down period is shortened by 13% and 7.5% for a single element and the 80-element array, respectively. In addition, the axial distance sensing resolution is increased by 30% and 25% for the single element and the array structure, respectively. These results demonstrate the effectiveness of the proposed scheme for applications at a short distance and/or high axial resolution, including short-distance medical ultrasonic imaging, fingerprints, gesture identifications, and 3D imaging.