Application of acoustic phase conjugate waves to the distortion-free ultrasonic imaging and self-targeting system for medical purposes

超声相位共轭现象因其在无损检测、医学超声等方面的潜在应用而引起人们极大的兴趣。相位共轭波的时间反演特性对波前扰动的自动校正具有重要作用。相位共轭波可以用来校正无损检测仪器或诊断系统中的图像畸变。时间反转波也将应用于自聚焦系统，用于治疗癌细胞或膀胱结石。在我们以前的工作中，我们已经开发了一种新的PZT陶瓷的超声相位共轭器，成功地在可视化的相位共轭波的时间反转传播，并显示了一个可能的应用程序的超声NDI或医疗器械。本研究的主要目的是：a）利用PZT相位共轭器构建超声成像系统，实现无畸变成像; B）利用时间反转波构建自聚焦超声成像系统。1)我们制作了一个装有PZT陶瓷相位共轭器的扫描成像系统，工作频率为15 MHz，对比了正常图像和相位共轭图像，发现相位共轭图像成功地校正了正常图像中明显的图像失真。2)我们将PZT相位共轭器的反射率提高到100%。3)为了研制实用的自聚焦系统，必须研制效率超过100%的相位共轭器。为此，我们测试了新型压电单晶PZNT（弛豫介电晶体）的压电性和介电性的三阶常数。我们发现它具有很高的非线性，是相位共轭放大器最有希望的材料。

The phenomenon of ultrasonic phase conjugation has attracted a great interest for its potential applications, for example, to non-destructive inspection and medical ultrasonics. The time reversal property of the phase conjugate waves has the important ability of the automatic correction of the wave front disturvance. Image distortion in the NDE (Non-Destructive Evaluation) apparatus or diagnosis system will be corrected by the phase conjugate waves. The time reversal waves will also been applied to the self-focussing system for the medical treatment against cancer cells or bladder stones. In our previous works, we had developed a new ultrasonic phase conjugator of PZT ceramics ; succeeded in the visualization of the time reversal propagation of the phase conjugate waves ; and shown a possible application to the ultrasonic NDI or medical apparatus. In the present research, we aimed to a) construct a ultrasonic imaging system with the PZT phase conjugator and establish a distortion-free-imaging ; and b) develop a self-focussing system with the time reversal waves.In these two years, we attained the following results. 1) We made a scanning imaging system that was equipped with the PZT ceramic phase conjugator operating at 15 MHz, compared the normal image with the phase conjugate image, and found that the image distortion obvious in the former was successfully corrected in the latter. 2) We increased the reflectivity of the PZT phase conjugator to 100% in intensity. 3) In order to develop a self-focussing system of practical use, a phase conjugator with efficiency exceeding 100% would be inevitable. For this purpose, we tested the new piezoelectric single crystal PZNT (relaxer dielectric crystal) add measured the third-order constants of piezoelectricity and dielecricity. We found the very high non-linearlity and showed that it could be the most expecting material for the phase conjugate amplifier.