Patent ID: 7542579

Claim:
An electrostatic ultrasonic transducer of a push-pull system comprising: a fixing electrode, a circular through hole being arranged in a central portion of said fixing electrode and providing a passage from a front face to a rear face of the ultrasonic transducer, wherein the circular through hole defines an axis of the circular through hole, wherein an outside diameter of said hole is set to ½ or more of an outside diameter of said fixing electrode; a sound wave reflecting plate arranged on the rear face of the ultrasonic transducer, wherein an ultrasonic wave radiated from the rear face of the ultrasonic transducer is reflected by said sound wave reflecting plate and is radiated to the front face of the ultrasonic transducer through said through hole; a moving mechanism for moving a position of said sound wave reflecting plate forward and backward along the axis of the circular through hole; and a moving mechanism control means for controlling said moving mechanism to adjust a moving amount of said sound wave reflecting plate from the rear face of said ultrasonic transducer in accordance with a frequency of an ultrasonic carrier wave signal for opening said ultrasonic transducer.