Analysis, modeling and design of piezoelectric-capacitive hybrid micromachined ultrasonic transducer

This paper proposes a spring-mass-damper model for a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer (HMUT) in immersion. Based on this model, a dual-force actuation mode is identified, where piezoelectric micromachined ultrasonic transducer (PMUT) and capacitive micromachined ultrasonic transducer (CMUT) are strongly coupled to achieve enhanced sensitivity. In order to design HMUT efficiently, an electro-mechanical-acoustical equivalent circuit model (ECM) is constructed and then the round-trip gain is calculated to demonstrate its pulse-echo response. The ECM calculations results align with those of finite element model simulations, showing a relative deviation less than 4%. In the design cases, the transmit sensitivity of HMUT is twice that of PMUT and more than five times that of CMUT. The receive sensitivity of HMUT is 1% lower than that of CMUT, but an order of magnitude larger than that of PMUT. The round-trip gain of the HMUT is at least 24.9 dB higher than that of PMUT and 14.1 dB higher than that of CMUT. These results demonstrate the potential of HMUT in surpassing bulk piezoelectric ultrasonic transducers in pulse-echo imaging. Furthermore, the impact of cell pitch on the pulse-echo response of HMUT arrays is characterize.