Patent ID: 7949143

Claim:
An ultrasonic speaker comprising: an electrostatic ultrasonic transducer of a push-pull system including: 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 through 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 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 operating said ultrasonic transducer, wherein said sound wave reflecting plate is arranged on the rear face of said ultrasonic transducer; said sound wave reflecting plate has a first reflecting face for reflecting the sound wave radiated from the rear face of the ultrasonic transducer in a direction parallel to the sound wave radiating face of the ultrasonic transducer and a central direction of the ultrasonic transducer, and a second reflecting face for reflecting the sound wave radiated from said first reflecting face in the direction of the sound wave radiating face of the ultrasonic transducer, wherein said moving mechanism control means adjusts the moving amount of said sound wave reflecting plate through said moving mechanism such that a difference in carrier path length between the ultrasonic wave directly radiated from the front face of said ultrasonic transducer and the ultrasonic wave radiated from the rear face of said ultrasonic transducer and reflected on said sound wave reflecting plate becomes n·λ+λ/2 (n is an integer) when a wavelength of said ultrasonic carrier wave signal is set to λ.