Abstract
The motion of high-intensity aerial converged ultrasonic waves (frequency: 20 kHz) as studied as they entered a perforation which had a smaller diameter than the wavelength of the radiated acoustic waves (approx. 17.4 mm). In addition, the characteristics of the sound field created in the perforation were studied experimentally. The acoustic waves incident upon the perforation were convergent, having a spreading angle of approx. 90°. As a result, it was elucidated that the acoustic waves favorably entered the perforation with a sufficiently smaller diameter (5 mm max) than the wavelength of the acoustic waves. A sound field of standing waves was created with the sound pressure being the maximum at the bottom of the perforation. The sound pressure increased in the ratio of the 0.5th power of the electric power supplied to the sound source. When the electric power supplied to the sound source was 50 W, a very powerful ultrasonic field of approx. 170 dB was created at the bottom of the perforation.