Modeling and design of CMUTs using higher order vibration modes [capacitive micromachined ultrasonic transducers]

Capacitive micromachined ultrasonic transducer (CMUT) design has so far relied on the first vibration mode of the CMUT membrane which most resembles piston-like motion. However, experiments show that the frequency response of the CMUT is significantly affected by the higher order vibration modes of the membrane. In this paper, we discuss the design of CMUTs considering these higher order vibration modes of the transducer membrane to tailor its frequency response for specific applications such as harmonic imaging. Based on an FEA model, we show that the vibration frequency of a particular membrane mode can be adjusted by judicious mass loading of the membrane, taking the strain energy distribution into account. Furthermore, we show that using multiple electrodes on the CMUT membrane, in conjunction with membrane mass distribution, the transmit and receive response of the CMUT can be separately optimized for harmonic imaging. An example is given to illustrate the above concepts.