Patent ID: 7668323

Claim:
A push-pull type electrostatic ultrasonic transducer comprising: a vibrating film having a conductive layer; a sound insulating cover; and a pair of fixed electrodes including a front-side fixed electrode and a rear-side fixed electrode that sandwich respective surfaces of the vibrating film, a direct current bias voltage is applied to the conductive layer of the vibrating film by a direct current bias supply and an alternating current signal is applied to the fixed electrodes to allow the vibrating film to generate a sound wave and output the sound wave generated from the vibrating film from two sound wave output surfaces via a plurality of through holes provided in the respective pair of fixed electrodes, wherein the plurality of through holes provided in the front-side fixed electrode and the plurality of through holes provided in the rear-side fixed electrode have the same shapes and are provided in an opposed relationship; wherein the sound insulating cover is provided facing the rear-side fixed electrode at a predetermined distance from a surface thereof; and wherein a distance L between the rear-side fixed electrode and the sound insulating cover is set based on L =( c/ 2 πf ) 2 ·a /( t +δ), where f is an ultrasonic carry wave frequency at the time of rated driving, c is sound speed, a is an aperture ratio of a through portion of the rear-side fixed electrode, t is a thickness of the through portion of the rear-side fixed electrode, and δ is open-end correction constant depending on an aperture shape of the through portion.