5F-1 Analytical Models for Micromachined Transducers - An Overview (Invited)

Over the past decade, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as a viable alternative to existing piezoelectric ultrasonic transducers in some applications within ultrasonic nondestructive evaluation, gas flow metering, and diagnostic medical imaging. These transducers, which can transmit and receive ultrasound in fluid media, offer wide signal bandwidths and have potential advantages in fabrication of high-frequency arrays and integration with electronics. Accurate simulation and modeling of CMUTs transducers is critical to designing efficient transducer for a particular application, as the number of available design parameters is high. Although modeling techniques such as finite-element methods (FEM) are invaluable for predicting the behavior of such complex systems, more approximate analytical techniques may offer greater insight with significantly less time and effort. Techniques such as lumped equivalent circuit modeling are often the starting point for analyzing tradeoffs amongst designs and understanding measurement results. This paper surveys the most common analytical modeling techniques, largely based on linear, lumped, equivalent circuit models for CMUTs in air and water. Some potential extensions are proposed to account for fluid loading, high-order vibrational modes, and membranes composed of multiple material layers. In addition, we investigate the effects of variations among individual CMUT membranes within a transducer on measurements and performance, whether intentional or as an undesired result of fabrication nonuniformities