| Project/Area Number |
09650487
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
計測・制御工学
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| Research Institution | Tokai University |
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Principal Investigator |
SAITO Shigemi Tokai University, Faculty of Marine Science and Technology, Professor, 海洋学部, 教授 (50091690)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 1998: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Keywords | ultrasound / nonlinear acoustics / acoustic microscope / second harmonic sound / dispersion / nonlinearity parameter / finite-amplitude method / Gaussian source |
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| Research Abstract |
When a weakly dispersive layer is inserted into the focal region, a phase advance occurs for the second harmonic component passing through the layer due to slightly higher sound-speed for second harmonic frequency, together with the phase delay due to diffraction. Then the effects of the phase-mismatching and destructive-interference are weakened to result in amplitude increase of the second harmonic component in the postfocal region. The experiment for a layer of water-oil mixture with various oil fractions employed as a weakly dispersive liquid is compared with non-dispersive case and demonstrates the validity of theoretical prediction. When a focused ultrasound is applied to the finite-amplitude method to estimate the nonlinearity parameter B/A in dispersive liquid, it can, therefore, be overestimated. The methods used to measure the sound-speed difference between the fundamental and the second harmonic frequencies using the same focusing system and to measure the B/A accurately are presented. As an example of dispersive samples, the acoustic nonlinearity parameter B/A in water-oil mixtures at the gel state has been measured. The gel is obtained by mixing various amounts of gelatin powder together with small amount of formaldehyde to the warmed mixture sol. The B/A value is not changed by the solidification. To realize the B/A measurement method for small volume samples, the trial production of a 20-MHz focusing Gaussian source has also been conducted. A piezoelectric plate of LiNbO_3 of 0.19-mm thickness is bonded to a plane surface of solid acoustic lens made from synthetic silica glass, with an electrode fabricated through photo-etching technique to have a shape of star. The formation of focused Gaussian beam is confirmed through observation of near field of the fundamental and propagation of the nonlinearly generated second harmonic.
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