Micromachined ultrasonic transducers (MUTs)

The fabrication and modeling of ultrasonic air transducers is reported. The transducers are made using surface micromachining techniques, which enable the realization of capacitive transducers with center frequencies ranging from 1 MHz to 12 MHz. Transmission experiments in air at 3.1 MHz, 5.6 MHz, 9.2 MHz, and 11.4 MHz are reported. Custom circuitry is able to detect capacitance fluctuations on the order of 10^-18 F and fluctuating as fast as 20 MHz. The transducers can be optimized for either transmission or reception. By leveraging the precise structural control provided by micromachining, receivers with displacement sensitivity well in the sub-angstrom range can be fabricated. Such detection sensitivity is shown to yield transducer systems with a 100 dB signal to noise ratio. An improved theoretical model for the transducers is presented. The theoretical model describes the static behavior of the membrane. Theoretical predictions of the dynamic behavior of the membrane also agree well with experimental results