The influence of acoustic damping on the transformation efficiency of capacitive micromachined ultrasonic transducer in air

摘要

Acoustic damping of a capacitive micromachined ultrasonic transducer (CMUT) in air causes mechanical impedance to the membrane vibration, which significantly influences the transformation efficiency of the device. We observed the effect of acoustic damping on the transformation efficiency of a CMUT under various external acoustic pressure and device structure conditions; the results were compared with other factors such as capacitance variations originating from the change in air-hole rate [area ratio (AR)] over the total membrane area. The damping ratio of the perforated membrane plate was computed for each acoustic pressure condition, and the results were introduced into calculations of the membrane displacement using the finite element method to take the squeeze-film damping effect into account. The Q factor and transformation efficiency of the CMUT under various AR for the membrane and dimension conditions of the device were studied; the acoustic damping effect is discussed in terms of design optimization.