Finite element analysis of mechanically amplified CMUTs

We introduce the possibility of improving a single-cell capacitive micromachined ultrasonic transducer (CMUT) for air-coupled ultrasound by simply adding a hollow conical-shaped structure (horn) on top of the CMUT plate. The main objective is to improve both transmit and receive sensitivity by lowering the center-to-average displacement ratio, which for bending plate operated devices inherently is limited. In addition, for receive mode the force generated from the impinging sound pressure wave is concentrated to the center of the plate, resulting in larger signals and, in contrast to piston-shaped plates, the horn has the advantage of only moderately increasing the modal mass of the structure. By using finite element analysis and first sound pressure measurements of our modified CMUT, we demonstrate that this idea is feasible and promising for air-coupled CMUTs operating at frequencies below 150 kHz, as it has been been proven to be successful for commercially available piezoelectric-driven bending plate devices as well.