| 摘要 |
PROBLEM TO BE SOLVED: To efficiently improve the sound pressure of an audible speech self-demodulated from ultrasonic waves, when ultrasonic waves are emitted by amplitude-modulating the carrier the waves of ultrasonic band by the audible speech. SOLUTION: An amplitude modulator 2 generates a carrier-wave signal, having a frequency increasing the product of the sound pressure of carrier waves and the sound pressure of a side band, in the sound-pressure frequency characteristics of an emitter 4 and amplitude-modulates the carrier-wave signal by a speech signal from a speech generator 1. The amplitude-modulated signal is amplified by an amplifier 3, ultrasonic waves are emitted from the emitter 4, and the sound pressure of the audible speech self-demodulated from ultrasonic waves is enhanced. COPYRIGHT: (C)2008,JPO&INPIT
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