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Paper Abstract and Keywords
Presentation 2007-08-24 14:10
Evaluation of Directional Resolution of Spherical Biconcave Acoustic Lens for Ambient Noise Imaging on Small Scale Trial
Kazuyoshi Mori, Hanako Ogasawara, Toshiaki Nakamura (NDA) US2007-32
Abstract (in Japanese) (See Japanese page) 
(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 2.0 m, -3 dB 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 2.0 m has sufficient resolution for realizing the ANI system; for example, the beam width is 1 deg at 60 kHz. 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 400 mm and a radius of curvature of 500 mm. A burst pulse of 5 cycles at 300 kHz, 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 -3 dB 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) 
(in English) Ambient Noise Imaging / Acoustic Lens / FDTD Method / Reduced Scale Trial / Directional Resolution / / /  
Reference Info. IEICE Tech. Rep., vol. 107, no. 200, US2007-32, pp. 25-30, Aug. 2007.
Paper # US2007-32 
Date of Issue 2007-08-17 (US) 
ISSN Print edition: ISSN 0913-5685    Online edition: ISSN 2432-6380
Copyright
and
reproduction		 All rights are reserved and no part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Notwithstanding, instructors are permitted to photocopy isolated articles for noncommercial classroom use without fee. (License No.: 10GA0019/12GB0052/13GB0056/17GB0034/18GB0034)
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Conference Information
Committee US  
Conference Date 2007-08-24 - 2007-08-24 
Place (in Japanese) (See Japanese page) 
Place (in English) The Port and Airport Research Institute 
Topics (in Japanese) (See Japanese page) 
Topics (in English) Underwater Acoustics 
Paper Information
Registration To US 
Conference Code 2007-08-US 
Language Japanese 
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 Small 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  
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1st Author's Name Kazuyoshi Mori  
1st Author's Affiliation National Defense Academy (NDA)
2nd Author's Name Hanako Ogasawara  
2nd Author's Affiliation National Defense Academy (NDA)
3rd Author's Name Toshiaki Nakamura  
3rd Author's Affiliation National Defense Academy (NDA)
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Speaker Author-1 
Date Time 2007-08-24 14:10:00 
Presentation Time 30 minutes 
Registration for US 
Paper # US2007-32 
Volume (vol) vol.107 
Number (no) no.200 
Page pp.25-30 
#Pages 6 
Date of Issue 2007-08-17 (US) 

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