Patent ID: 7804971

Claim:
An electrostatic ultrasonic transducer comprising: a first electrode provided with a through hole; a second electrode provided with a through hole forming a pair with the through hole of the first electrode wherein an alternating current signal is applied between the first electrode and the second electrode; an oscillation film sandwiched between the pair of electrodes and having a conductive layer wherein a direct current bias voltage is applied to the conductive layer; and a holding member for holding the pair of electrodes and the oscillation film, wherein a value “a” of one side amplitude of the film oscillation is obtained by the following formula: a =(1 /πf )√{( I o ·10 P/10 )/2ρ o c} wherein I o denotes the reference acoustic intensity, the reference acoustic intensity being 0.96×10 −12 (W/m 2 ), ρ o is the density of the air, the density of the air being 1.2 (kg/m 3 ) and c denotes the sound speed in the air, the sound speed in the air being around 340 (m/S), when it is assumed that the outputted desired sound pressure is P (dB), the driving frequency is f (Hz) and the value of one side amplitude of the film oscillation of the oscillation film, which is being driven, is “a” (m), and a height of a step part provided in an outer circumference of the through hole on the respective oscillation film sides of the pair of electrodes in a direction of the oscillation film side is set at a value exceeding and close to the one side amplitude value “a”.