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

本文分析了聚焦声入射到靠近焦点的液体或固体层时的非线性声场。还介绍了在声学测量中的应用。假定声源处为正弦波的球形聚焦声。当声源振幅径向阴影为高斯函数时，在高次谐波分量也呈高斯分布的近似下，控制声束的KZK方程的解得到了显著简化。分析很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，有利于声的非线性传播在声学测量中的实际应用。当在聚焦场中插入一块固体薄板时，由于满足激发兰姆波条件的斜入射波可以穿透薄板， ...更多信息 Ve变得不同于入射波。在反射之前和之后非线性地产生的高次谐波被叠加到反射的高次谐波。当聚焦场中加入液体层时，即使源能级相对较低，（1+B/2A）/rhoc ^3较大的液体样品也会产生较大幅度的高次谐波。利用这一原理，提出了小体积样品非线性声学参数B/A的测量方法。用一个具有较高聚焦增益的声源代替水中聚焦场的一小部分，在样品外观察到声压的基波和二次谐波分量的幅值和相位的变化。一个新的值。定义参数R_F。将此值与理论R_F值进行比较，可得到使理论R_F值与实验R_F值相吻合的B/A值。本文还讨论了由于样品中速度弥散引起的测量误差。虽然较高的聚焦增益会使可测量的样品变小，但较高的基频会减小样品体积。因此，利用高频超声，本方法可发展成为对材料如生物组织的B/A特性进行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