Abstract
In this work, novel airborne capacitive micromachined ultrasonic transducers (CMUTs) based on a dual-backplate (DBP) technology are presented. In contrast to conventional CMUTs, these transducers use a three-electrode-based capacitive system, where the membrane is placed between two highly-perforated counter electrodes, enabling enlarged displacement amplitudes in electrostatic actuation and wide and tunable bandwidth due to a ventilated air cavity. Fabricated DBP-CMUT prototypes therefore show exceptionally high receive and transmit sensitivities of -34.5 dB(V/Pa) and 259 nm/V, respectively, in their 84 kHz resonance. The viscous dissipation introduced by ventilating the cavity results in a wide factional bandwidth (FBW) of 29%. An applicability of the developed CMUT for airborne ranging is demonstrated in pulse-echo based ranging measurements, where the distance of a sound reflecting metal plate can be clearly detected by a single CMUT operated in a transceiver mode.
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