Air-coupled ultrasonic bending plate transducer with piezoelectric and electrostatic transduction element combination

We present a simulation of an ultrasonic transducer element with piezoelectric and electrostatic transduction combined and with two bending plates. It combines the high SPL of a piezoelectric transducer with the tunable resonance frequency of a CMUT due to spring softening effect. In this work, we compare two state-of-the-art transducers with our approach: First, a piezoelectric bending plate transducer, based on a Murata MA40S4S transducer; second, a piezoelectric bending plate positioned above an additional electrode (piezoelectric and electrostatic transduction principle combined) and, third, a new structure, based on two bending plates with piezoelectric and electrostatic transduction combined (piezoelectric and electrostatic double-bending plate transducer). We use COMSOL Multiphysics 5.4 for creating a multiphysical model, including the electrical, mechanical and acoustical domain. We simulate mechanical total displacement and the directivity pattern. Thermoviscous losses in the air gap between the two bending plates are considered as well. The double-bending plate transducer has an increased amplitude of up to 570% at 80% of the pull-in voltage and a tunable resonance frequency of up to 21%. Compared to piezoelectric and electrostatic bending plate transducer, the total displacement is doubled. In addition, the radiation pattern is approximately omnidirectional, and, thus, beneficial for various applications such as obstacle detection, flow metering, distance measurement or anemometry.