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和医学超声等方面的潜在应用而引起了人们的极大兴趣。相位共轭波的时间反转特性具有自动校正波前扰动的重要能力。在无损检测设备或诊断系统中，相位共轭波可以对图像畸变进行校正。时间反转波也将被应用于治疗癌症细胞或膀胱结石的自聚焦系统。在前期工作中，我们开发了一种新型的PZT陶瓷超声相位共轭器；成功地实现了相位共轭波时间反转传播的可视化；并展示了超声波NDI或医疗器械的可能应用。在本研究中，我们的目标是a)构建PZT相位共轭器的超声成像系统，并建立无畸变成像；b)利用时间反转波开发自聚焦系统。在这两年中，我们取得了以下成绩：1)我们制作了一个装有工作频率为15mhz的PZT陶瓷相位共轭器的扫描成像系统，对比了正常图像和相位共轭图像，发现前者明显的图像畸变在后者中得到了成功的校正。2)将PZT相位共轭器的反射率提高到100%。3)为了研制出实用的自聚焦系统，必须研制出效率超过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），并测量了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，并表明它可能是相位共轭放大器最期望的材料。

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.