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

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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.