Active Acoustic Impedance Matching using CMUT Structure

Active acoustic impedance matching using capacitive micromachined ultrasonic transducer (CMUT) structure was successfully fabricated. The features of the fabricated device are the CMUT structure and tapered trench structures under the CMUT, it is possible to actively change the acoustic impedance viewed from the contacting sound propagation medium side using the collapse phenomenon of the CMUT. The tapered wall with heights of 900 microns was formed through deep reactive process. Acoustic transmittance of the fabricated device was evaluated by simulation and experiment. In the non-collapse state, sound waves were largely reflected near the resonance frequency of the membranes of CMUTs, whereas in the collapse state, a broad band and high transmittance were observed compared with a quarter wavelength matching method.