UC Berkeley

Micromachining technologies have enabled exciting applications in a small form-factor for ultrasonic transducers in medical imaging, range finder, human machine interface, and more. With the advantages in low size, weight, power and cost micromachined ultrasonic transducers are potential alternatives to bulk ultrasonic transducers. This work studies design of high performance piezoelectric micromachined ultrasonic transducers (pMUTs) for several applications.A free-clamped boundary pMUT has been proposed, which results in more than 16x higher electromechanical coupling coefficient and 100% electrode coverage area as compared with those of conventional clamped-clamped boundary pMUTs with only 67% electrode coverage area. The cavity in the free-clamped boundary design is also utilized as an acoustic resonator to increase 10-100x larger bandwidth as compared with those of conventional pMUTs with clamped-clamped boundary. Furthermore, a two-term mode shape approach for the conventional clamped pMUTs is presented to result in an improved lumped element model for less than 0.5% error in the intrinsic and extrinsic properties of pMUT including equivalent circuit parameters, input impedance, velocity, displacement, bandwidth, directivity, and the on-axis pressure in the near and far fields. First, an ultrasound-induced airborne haptic device via pMUTs is demonstrated by modulating the high frequency ultrasound into a low frequency patterns to stimulate mechanoreceptors inside the human skin. Results show that the human haptic sensations from volunteers can achieve 80% and 76% identification accuracy for the switching on/off and Morse code patterns, respectively. Second, structures with curved surfaces are studied for two properties: (1) the signal attenuation due to the curved surface; and (2) the radius-of-curvature (RoC) measurement by using the time-of-flight scheme. Results show good matches between the measured and simulated attenuation at 25 mm away due to the curvature as 7 dB. Good RoC measurement accuracies for 3D-printed curved surfaces have also been achieved up to 200 mm at a distance 5 cm away. Lastly, a phase-shift cancellation scheme is proposed to reduce the ring down period and increase axial resolutions. Results show the ring down period is shortened by 13% and 7.5% and the axial distance resolution is increased by 30% and 25%, for a single element and an 80-element array, respectively.