Airborne ultrasonic electrostatic transducers with conductive grooved backplates: tailoring their centre frequency, sensitivity and bandwidth

Several electrostatic transducers with metallic backplates have been manufa ctured. Some backplates have been subjected to coarse polishing, whereas ot hers were first polished and then rectangular grooves were machined. Experi mental investigations have been performed in order to study the influence o f the groove widths, their layout and the value of DC bias on the transduce r behaviour. These results are compared with theoretical predictions using the Helmholtz resonator model. The equation of the vibration of a membrane submitted to a mechanical stress, but neglecting the effects of its elastic ity, was also compared with experimental results. This shows that the Helmh oltz resonator model is adapted to the behaviour of the polished backplates , whereas the membrane model explains the vibration over the grooves. By ch oosing the groove widths and layout (i.e. polished to grooved-surface ratio ), the centre frequency, the bandwidth and the sensitivity of the transduce r can be optimised for a given application. (C) 1999 Elsevier Science B.V. All rights reserved.