Creation of Acoustic Field in Linear or Partially Bent Holes by High-Intensity Aerial Convergent Ultrasonic Waves

Using high-intensity convergent ultrasonic waves (frequency: 19.65 kHz; wavelength: 17.6 mm), a study was conducted on basic properties resulting from these acoustic waves entering linear holes with cross-sectional dimensions being less than 1/4 of the wavelength of the acoustic waves. The sound field formed inside the holes, whose length ranged from 2 to 60 mm, had the same characteristics as that formed when plane waves entered an acoustic tube with a closed end. In addition, even when the hole had a bent part of up to 90°, it was possible for the convergent acoustic waves to enter the hole. In this case, extremely high-intensity ultrasonic waves of approximately 174 dB were created at the bottom of the hole.