Miniature drumheads: microfabricated ultrasonic transducers

Significant improvement in the performance of capacitive microfabricated ultrasonic transducers is reported and the modifications which enable the progress are described. Air-coupled through-transmission of glass and steel at 2.3 MHz is demonstrated for the first time. Furthermore, a 20 μm step on a silicon wafer is detected with both amplitude and phase signals at 3 MHz. The same process used to fabricate the air transducers also yields immersion transducers, which are reported to operate in water from 1 to 20 MHz with a dynamic range of 60 dB measured at 3 MHz. It is anticipated that optimized immersion transducers will be able to achieve the 110 dB dynamic range of the air transducers. A brief review of the theoretical modeling of the device is also presented.