A Study of Aspherical Convex Lens with Solid-Liquid Compound Structure for Underwater Object Imaging Using Ocean Ambient Noise

2021 Fiscal Year Final Research Report

• Project/Area Number: 18K04597
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 24020:Marine engineering-related
• Research Institution: 防衛大学校(総合教育学群、人文社会科学群、応用科学群、電気情報学群及びシステム工学群)
• Principal Investigator: Mori Kazuyoshi 防衛大学校(総合教育学群、人文社会科学群、応用科学群、電気情報学群及びシステム工学群), 応用科学群, 教授 (70259894)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 海洋科学 / 海洋工学 / 海洋探査 / 音響レンズ / 海中周囲雑音 / 物体映像化 / 非球面レンズ / 凸レンズ

Outline of Final Research Achievements

A novel idea, which views ambient noise as a sound source, is often called ambient noise imaging (ANI). For surveying underwater objects in a vast expanse of ocean using ANI, it is necessary to mount an acoustic lens into a movable underwater vehicle. The convex lens is desirable to mount it on the bow of underwater vehicle. In this study, the convex lens with solid-liquid compound structure composed with solid lens faced to sea water, and inner liquids placed in the bow is proposed.
First, we measured the sound velocities of some materials for applying to the proposed lens. The lens aspherical surfaces were determined by the refractive indexes based on the measured values. We also analyzed the sound pressure field converged by the lens to predict its performances. As compare with the results of the small-scale trial in water tank, the predicted values of focal point and convergence gain were mostly agreed with those. These results could be a basis to applying ANI to a vast of ocean.

Free Research Field

海洋音響工学

Academic Significance and Societal Importance of the Research Achievements

周囲雑音イメージングは，計測側から音波を放射する必要がなく，対象物体自身が音波を放射していない無音状態でも探知が可能である．この特徴は隠密裏に対象物体を探知するのに適している．本研究を発展させることで周囲雑音イメージングの水中航走体への搭載を実現し，広大な海域における水中セキュリティや音に敏感な海洋生物調査などの応用面での可能性を広げることが期待される．