Proof of concept of an air-coupled electrostatic ultrasonic transducer based on lateral motion

Abstract

An alternative implementation of an electrostatic MUT (Micromachined Ultrasonic Transducer), relying on multiple beams that displace along the chip’s surface instead of a single membrane displacing perpendicular to it, is presented in this work. With this approach, a design requiring a low bias voltage (24 V) and occupying a small area (3.3 ×3.3 mm², 2 D / λ ≈ 0.77 ) was shown to generate a sound pressure level of 82 dB (re. 20 µPa-rms) at 40 kHz and a distance of 8.9 cm. The high level of damping allows this transducer to operate in a wide frequency range (35–63 kHz). The operation of this device as an ultrasonic receiver was also proven. An implementation of this transducer as a rangefinder requires a strong reduction in the noise level, particularly coming from radio-frequency interference, in order to increase its detection range. • A transducer concept based on lateral motion (instead of vertical) is used for transmitting and receiving airborne ultrasound. • A high fluidic damping was observed, enabling a transmission bandwidth of nearly an octave (35–65 kHz). • This electrostatic device is based on an array of microbeams and has a sidelength smaller than half a wavelength.