A rotational capacitive micromachined ultrasonic transducer (RCMUT)

An unconventional acoustic sensor is presented with audio and ultrasound applications. The structure is a synthesis of capacitive micromachined ultrasonic transducer (CMUT) technology and biologically inspired microphones which use rotational or rocking modes of vibration to directly sense acoustic pressure gradient. A pivoting beam structure is sealed under vacuum, and the top surface of the beam is driven into motion by external pressure gradients. Vvacuum sealing eliminates the introduction of excessive damping, stiffness, and thermal mechanical noise into the system. Motion of the beam is transduced capacitively at each end of the beam using gap-closing parallel plate electrodes. Surface-micromachined prototypes are presented that are 470 μm × 718 μm in size and exhibit a fundamental rocking resonance at 480 kHz, and a second flapping mode at 630 kHz, for which both ends of the beam vibrate in phase.