Diffraction in finite-amplitude focusing sound field and its application to acoustical imaging.
| Project/Area Number |
61550283
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
電子機器工学
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| Research Institution | Tokai University |
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Principal Investigator |
SHIGEMI Saito Faculty of Matine Seience and Technology, Tokai University, 海洋学部, 助教授 (50091690)
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| Project Period (FY) |
1986 – 1987
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| Project Status |
Completed (Fiscal Year 1987)
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| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1987: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1986: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Keywords | Focusing Source / Nonlinearity Parameter / Nonlinear Acoustics / 超音波顕微鏡 |
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| Research Abstract |
A sinusoidal sound wave emitted by a spherically focusing source distorts in waveforms with propagation toward the focus mainly due to the elastic nonlinearity of the medium, which can be described with the nonlinearity parameter. It was theoretically and experimentally proved that the largest part of the second harmonic component seen at the post focal region was generated in the focal region, because the secound harmonic components generated in the preand post-focal region cancel each other affected by the phase shift of the sound wave passing through the focus. Inserting a sample whose nonlinearity parameter differs from that of surrounding medium (water) into the focal region, the magnitude of the second harmonic component with the phase parameter of <pi>/2 radians seriously changes. This leads to the possibility to detect and visualize how the nonlinearity parameter of samples immersed in the focus differs from water. On the other hand, since the wavf propagation of a cylindrically focusing source does not suffer a similar phase shift the second harmonic component generated at eh focal region cannot be dominant in the post focal region. Therefore only the spherically focused sound may be appropriate for the present research project. Assuming a general case where the linear parameters (the ambient density, the sound speed, and the absorption coefficient) of the sample differed from those of surrounding medium as well as the nonlinearity parameter, the influence of the sample on the sound wave was theoretically and experimentally discussed. The result shows that the second harmonic component observed in the post focal region strongly depends on the linear acoustic parameters as well as on the nonlinerity parameter. However the method to estimate the nonlinearity parameter when both the density and sound speed are known has been shown. The realization of a gaussian focusing source will hoprfully make possible to visualize the nonlinerity parameter of the sample.
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Report
(2 results)
Research Products
(15 results)
