The Journal of the Marine Acoustics Society of Japan
Online ISSN : 1881-6819
Print ISSN : 0916-5835
ISSN-L : 0916-5835
Volume 50, Issue 3
Displaying 1-1 of 1 articles from this issue
Paper
  • Shoko TANABE, Yuji SATO, Tadashi EBIHARA, Naoto WAKATSUKI, Koichi MIZU ...
    2023 Volume 50 Issue 3 Pages 56-66
    Published: July 01, 2023
    Released on J-STAGE: January 25, 2025
    JOURNAL FREE ACCESS

    Acoustic lenses, which focus sound waves in water without using complicated electronic circuits, are attracting attention as a device to realize miniaturization and power saving of underwater acoustic cameras and sonar. The shapes of acoustic lenses vary widely, but they are designed based on optical theory. Therefore, it is often assumed that total reflection occurs when the angle of incidence exceeds the critical angle, and the transmission characteristics of acoustic lenses are often evaluated at the angle of incidence within the critical angle. However, since the thickness of an acoustic lens is thinner than that of an optical lens, the evanescent field may affect the transmission of sound waves through the lens even when the incident angle exceeds the critical angle. In this study, we designed a biconcave acoustic lens with multiple thicknesses and investigated the focusing characteristics of sound waves incident on the lens at angles exceeding the critical angle. Consequently, it was found that when the minimum thickness of the lens is about one-third of the wavelength, the sound wave penetrates the narrow part of the lens significantly, and the lens may function as a lens even beyond the critical angle.

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