| Presentation | 2007-08-24 Evaluation of Directional Resolution of Spherical Biconcave Acoustic Lens for Ambient Noise Imaging on Reduced Scale Trial Kazuyoshi MORI, Hanako OGASAWARA, Toshiaki NAKAMURA, |
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| PDF Download Page |  PDF download Page Link |
| Abstract(in Japanese) | (See Japanese page) |
| Abstract(in English) | Much attention has been paid to the new idea of detecting objects by using ocean ambient noise. This concept is called ambient noise imaging (ANI). Since an acoustic lens system would not require a large receiver array and a complex signal processing unit for two-dimensional beam forming, minimization would be facilitated and ANI system costs would be reduced. The authors analyzed the sound field focused by an acoustic lens system constructed with a single spherical biconcave lens using the Finite Difference Time Domain (FDTD) method to design an ANI system. The analysis to determine the size of the lens aperture was carried out in the last study. At an aperture of 2.0m, -3dB areas, which have less pressure than the maximum pressure at the image point, almost do not overlap each other at every degree of the incident angle. Therefore, the lens with an aperture size of 2.0m has sufficient resolution for realizing the ANI system; for example, the beam width is 1deg at 60kHz. In this study, to confirm the FDTD analysis result, we performed a reduced scale trial of one-fifth space in a water tank. The lens, made of acrylic resin, has an aperture of 400mm and a radius of curvature of 500mm. A burst pulse of 5 cycles at 300kHz, in which the frequency increases 5 times, radiated -from the sound source. The sound pressure after passage through the acoustic lens was measured by moving the receiver around the image point. The results show that the shape of -3dB area is similar to that of the FDTD analysis result at normal incidence, which suggests that this lens has sufficient resolution to use in an ANI system. |
| Keyword(in Japanese) | (See Japanese page) |
| Keyword(in English) | Ambient Noise Imaging / Acoustic Lens / FDTD Method / Reduced Scale Trial / Directional Resolution |
| Paper # | US2007-32 |
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| Conference Information | |
| Committee | US |
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| Conference Date | 2007/8/17(1days) |
| Place (in Japanese) | (See Japanese page) |
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| Topics (in Japanese) | (See Japanese page) |
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| Paper Information | |
| Registration To | Ultrasonics (US) |
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| Language | JPN |
| Title (in Japanese) | (See Japanese page) |
| Sub Title (in Japanese) | (See Japanese page) |
| Title (in English) | Evaluation of Directional Resolution of Spherical Biconcave Acoustic Lens for Ambient Noise Imaging on Reduced Scale Trial |
| Sub Title (in English) | |
| Keyword(1) | Ambient Noise Imaging |
| Keyword(2) | Acoustic Lens |
| Keyword(3) | FDTD Method |
| Keyword(4) | Reduced Scale Trial |
| Keyword(5) | Directional Resolution |
| 1st Author's Name | Kazuyoshi MORI |
| 1st Author's Affiliation | Department of Earth and Ocean Sciences, National Defense Academy() |
| 2nd Author's Name | Hanako OGASAWARA |
| 2nd Author's Affiliation | Department of Earth and Ocean Sciences, National Defense Academy |
| 3rd Author's Name | Toshiaki NAKAMURA |
| 3rd Author's Affiliation | Department of Earth and Ocean Sciences, National Defense Academy |
| Date | 2007-08-24 |
| Paper # | US2007-32 |
| Volume (vol) | vol.107 |
| Number (no) | 200 |
| Page | pp.pp.- |
| #Pages | 6 |
| Date of Issue | |