A rotational capacitive micromachined ultrasonic transducer (RCMUT) with an internally-sealed pivot

Most capacitive micromachined ultrasonic transducers (CMUTs) are comprised of individual gap-closing parallel plates. We present an unconventional CMUT in which a vacuum-sealed cavity beneath a diaphragm layer comprises a mechanical structure that pivots and has a first rocking or rotational mode of vibration. The general ability to couple individual CMUT pistons under vacuum with mechanical structures to alter vibration mode frequencies and mode shapes is thus demonstrated. The particular prototype presented spans a distance of 250 μm and has a first rocking mode of vibration at 480 kHz. As a transmitter, the first mode radiates ultrasound in-plane along the surface. Frequency response characterization of a prototype is performed using laser Doppler vibrometry, and a pair of devices is used to perform ultrasonic pitch-catch measurements spanning a distance of 5 mm.