| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1991: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1990: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
In the present research, nonlinear field of focused sound accompanied by the incidence of the sound into a liquid or solid layer set near the focus has been analyzed. An application to acoustic measurement has also been presented. A spherically focused sound of sinusoidal wave at the source is assumed. When the source amplitude is radially shaded as a Gaussian function, the solution for KZK equation governing the sound beam is significantly simplified under the approximation that the higher harmonic components also take Gaussian distribution. The analysis well describes the experimental results. The simplicity of the physical and mathematical properties of Gaussian beam is useful for the practical application of the nonlinear propagation of sounds to acoustic measurements. When a solid thin plate is inserted into the focusing field, since the obliquely incidence wave satisfying the condition to excite Lamb mode waves can penetrate through the plate, the beam pattern of the reflected wa
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ve becomes different from that of the incidence wave. The higher harmonics nonlinearly generated before and after the reflection are superposed to the reflected higher harmonics. when a liquid layer is inserted into the focused field, the liquid sample with large value of(1+B/2A)/rhoc^3 results in large amplitude of higher harmonics even if the source level is relatively low. Utilizing this principle, the measurement method for the acoustic nonlinearity parameter B/A of small volume sample has been presented. Replacing a small portion across the focal region of focused field formed in water by use of a sourcewith relatively high focusing gain, the changes in the amplitudes and phases of the fundamental and second harmonic components of the acoustic pressure are observed beyond the sample. The value of a newly. defined parameter R_F is obtained using the observed results. Through comparison of this value with the theoretical value of R_F, the value of B/A, which makes fit the theoretical RFon the experimental R_F, can be obtained. The measurement error of the present method due to the velocity dispersion in the sample is also discussed. Though the higher focusing gain makes the measurable sample smaller, 'the higher fundamental frequency can reduce the sample volume. Therefore, using high frequency ultrasound, the present method can be developed to the research tool for microscopic study on the B/A property of the materials such as biological tissues. Less
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