Experimental investigation of electrostatic ultrasonic transducers with grooved backplates

This paper presents an experimental investigation of electrostatic transducers with grooved backplates for airborne applications. These transducers consist of a micromachined conductor backplate covered with a metal-coated polymer film. Measurements such as pulse electro-acoustic response, electrical impedance and mechanical displacement field over the membrane have been performed. The influence of the groove layout on the transducer behaviour and its performances is studied. Two different behaviours in the spectral response are observed. One, due to the mechanical resonance of the membrane over the groove and the other one, produced by the polished backplate surface. A method to control the sensitivity and bandwidth of these transducers by an appropriate choice of the grooved surface ratio is proposed.