Bimorph Pinned Dual-Electrode Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) for Sensing and Actuation


Piezoelectric micromachined ultrasonic transducers (PMUTs) have advantages to those of traditional ultrasonic transducers in small form factor, low cost, low power consumption, large bandwidth, and good acoustic impedance matching. A bimorph pinned dual-electrode PMUT is developed for improved vibrational displacement, output sound pressure, and electro-mechanical coupling for several demonstration examples, including 3D space imaging, directional loudspeaker, and non-contact temperature sensing.

Analytically, an equivalent circuit model has been built for bimorph, pinned dual-electrode PMUTs and finite element simulation result has shown a 380% boost for the sound pressure per volt per area and increased center displacement at the resonant frequency as compared to those of conventional unimorph PMUTs. Experimentally, prototype devices have been designed, fabricated, and tested with a 58% measured increase in the electromechanical coupling factor and pulse-echo tests have shown a 4-meter traveling distance in air under a 133 kHz driving frequency. As a proof-of-concept, a long-distance (>1.5 meters) ultrasound imaging is demonstrated using a 4×4 array prototype system based on the transmit beamforming scheme in air. A small form factor (6×6 mm2) design and a more than 135o field of view have display the capability of real time 3D object detection with up to 125 fps (frames per second) based on the scheme of ultrasound receive beamforming toward applications such as drone navigation, machine vision and so on.

A highly directional air-coupled parametric loudspeaker using a single PMUT chip has been validated based on a parametric array design to generate highly directional audible sound with a half power beam width of less than 5 degrees. The multiple audible frequency sound has been generated by using a single chip with 246 PMUT elements in a footprint of 13 × 13 mm toward low-power and portable directional loudspeakers for private communications. In another example, non-contact surface temperature measurements via a single PMUTs array have been established based on the time-of-flight (ToF) changes. The key advantages of this scheme include the independence of surface material properties, e.g. emissivity; the possible integration with an ultrasonic analog front-end circuitry for both transmitting and receiving. A recorded sensitivity of 143 ns/oC has been achieved in non-contact temperature sensing in various media such as air, liquid, and tissue for broad applications.

Publication date: 
May 1, 2021
Publication type: 
Ph.D. Dissertation
Shao, Zhichun (2021). Bimorph Pinned Dual-Electrode Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) for Sensing and Actuation. (Doctoral dissertation) University of California, Berkeley.

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