Analysis of finite-amplitude focused sound field with reflection and transmission at a liquid of solid layer.

本研究分析了聚焦声的非线性场，并分析了聚焦声入射到焦点附近的液体或固体层。本文还介绍了该方法在声学测量中的应用。假设声源处的正弦波为球聚焦声。当声源幅值以高斯函数径向遮蔽时，在高次谐波分量近似为高斯分布的情况下，控制声束的KZK方程的解得到了显著的简化。分析较好地描述了实验结果。高斯波束的物理和数学性质的简单性，有助于声音的非线性传播在声学测量中的实际应用。当聚焦场中插入固体薄板时，由于满足激发兰姆模式波条件的斜入射波可以穿透薄板，因此反射波的波束模式与入射波的波束模式变得不同。反射前后非线性产生的高次谐波叠加到反射后的高次谐波上。当聚焦场中插入液体层时，即使源电平较低，(1+B/2A)/rhoc^3大值的液体样品也会产生较大的高次谐波幅值。利用这一原理，提出了小体积样品声学非线性参数B/A的测量方法。通过使用具有相对高聚焦增益的源，在水中形成的聚焦场的焦点区域中替换一小部分，在样品之外观察到声压的基频和二次谐波分量的振幅和相位变化。的值。定义参数R_F由观测结果得到。通过与理论R_F值的比较，可以得到与理论R_F和实验R_F相吻合的B/A值。文中还讨论了由于样品中速度色散所引起的测量误差。虽然较高的聚焦增益使可测样品变小，但较高的基频可以减小样品体积。因此，利用高频超声，本方法可以发展成为生物组织等材料B/A性质微观研究的研究工具。少

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 … More 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