Analysis of nonlinear focused sound field in dispersive media and its application to measurement.

色散介质中非线性聚焦声场分析及其测量应用

• 批准号: 09650487
• 负责人: SAITO Shigemi
• 金额: $ 1.92万
• 依托单位: Tokai University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1997
• 资助国家: 日本
• 起止时间: 1997 至 1998
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650487/
• 关键词: ultrasound; nonlinear acoustics; acoustic microscope; second harmonic sound; dispersion; nonlinearity parameter; finite-amplitude method; Gaussian source

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.

当在焦点区域插入弱色散层时，由于二次谐波频率的声速略高，通过该层的二次谐波分量会发生相位超前，同时由于衍射导致相位延迟。然后减弱相位失配和相消干涉的影响，使焦后区域的二次谐波分量振幅增大。将不同油分的水-油混合层作为弱分散液体与非分散情况进行了实验比较，验证了理论预测的有效性。因此，当聚焦超声应用有限振幅法估计分散性液体中的非线性参数B/ a时，可能会高估。介绍了用同一聚焦系统测量基频和次频声速差和精确测量B/A的方法。以色散样品为例，测量了凝胶状态下油水混合物的声学非线性参数B/A。将不同数量的明胶粉与少量甲醛混合到加热的混合溶胶中得到凝胶，B/A值不因凝固而改变。为了实现小体积样品的B/A测量方法，还进行了20 mhz聚焦高斯源的试制。将厚度为0.19 mm的LiNbO_3压电板粘接在合成硅玻璃固体声透镜的平面上，并通过光蚀刻技术制作出星形电极。通过观察基波的近场和非线性二次谐波的传播，证实了高斯光束的形成。

项目成果

Shigemi Saito: "Measurement of nonlinearity parameter in dispersive liquid using focused ultrasound." Japanese Journal of Applied Physics 37, Part 1. No.5B. 3035-3040 (1998)

Shigemi Saito：“使用聚焦超声测量分散液体中的非线性参数。”

Shigemi Saito: "Second harmonic component in the focused ultrasound transmitted through a weakly dispersive liquid layer." Proceedings of Joint ASA/EAA Meeting. (発表予定). (1999)

Shigemi Saito：“通过弱色散液体层传输的聚焦超声的二次谐波分量。”ASA/EAA 联合会议记录（待提交）。

Sigemi Saito: "Measurement of the nonlinearity parameter in dispersive liquid using focused ultrasound." Japanese Journal of Applied Physics. 37, 1-5B. 3035-3040 (1998)

Sigemi Saito：“使用聚焦超声波测量分散液体中的非线性参数。”

Shigemi Saito: "Second harmonic component in the focused ultrasound transmitted through a weakly dispersive liquid layer." Proceedings of Joint ASA/EAA Meeting. (To be published).(1999)

Shigemi Saito：“通过弱色散液体层传输的聚焦超声波中的二次谐波分量。”

Shigemi Saito: "Measurement of the nonlinearity parameter in dispersive liquid using focused ultrasound." Japanese Journal of Applied Physics. 37,1-5B. 3035-3040 (1998)

Shigemi Saito：“使用聚焦超声波测量分散液体中的非线性参数。”