Rotational Capacitive Micromachined Ultrasonic Transducers (cMUTs)

A rotational capacitive micromachined ultrasonic transducer is introduced. Two pressure-sensitive diaphragms atop vacuum-sealed cavities are mechanically coupled via a rocking beam structure. The rocking structure is designed to reduce deflection of the vacuum-sealed diaphragms under atmospheric pressure while introducing ideally zero rotational stiffness to differential diaphragm pressure. The rocking structure responds to in-plane pressure gradients and is therefore anticipated to have dipole-type directivity to ultrasound. Prototypes employing 200 μm diameter polysilicon diaphragms are presented with a fundamental resonance frequency of 250 kHz.