Electromechanical and Acoustic Characterization of a Capacitive Micromachined Ultrasonic Transducer in Multienvironment Conditions

A comprehensive study of the electromechanical coupling efficiency, acoustic pressure and frequency responses of capacitive micromachined ultrasonic transducer (CMUT) under varied structural and environmental conditions is presented. In this paper the effects of critical factors, including cavity thickness, membrane thickness and radius, and applied bias voltage, on the device's electromechanical coupling coefficient were examined using analytical modelling and finite element method (FEM) simulations. Significant deviation of 33% in resonant behaviour between water and air media was observed through frequency response analysis, which was brought about by different acoustic loading effects. Sound pressure level (SPL) and sound pressure distribution reflected notably improved performance in water. Temperature analysis reported a non-linear increase in sound pressure, from 100 Pa at −55 °C to about 300 Pa at 85 °C, with significant thermal sensitivity. The fabricated device showed excellent agreement with analytical model, at capacitance measured of 0.458 pF and resonant frequency at 2.8 MHz.