| 摘要 |
PROBLEM TO BE SOLVED: To facilitate arrangement of elements in an ultrasonic wave speaker that employs a piezoelectric element ultrasonic wave transducer to direct a beam. SOLUTION: An ultrasonic wave modulator modulates an ultrasonic wave signal with a central frequency (f) on the basis of an input of an audible signal. Many delay lines delay the modulated ultrasonic wave signal in order to direct a beam pattern toward an angleθ0 . A speaker outputs the ultrasonic wave signal by directing the beam pattern toward the angleθ0 . The ultrasonic wave speakers are placed so that a center distance (d) is greater than half the wavelengthλ/2 of the ultrasonic wave. Thus, the beam pattern has a main lobe and at least one grating lobe. The main lobe has a mode K and the grating lobe has an attenuation Ga with respect to the attenuation of the main lobe. Expression (1) holds between the values d, f, K, Ga, andθ0 , where c is a sound velocity.
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