Ultrasonic Imaging by the Phase Conjugate Resonance System

本研究是利用相位共轭波改进超声c型成像系统的尝试。利用压电陶瓷的非线性压电特性，设计了一种超声相位共轭器。该相位共轭器与波导一起安装在超声c型成像仪中。由于相位共轭波对任意入射波起时间逆波的作用，因此初始超声场保持其波前形状，就像在谐振器中一样。这种效应使超声图像对超声波前变形不那么敏感，但对超声阻尼仍然敏感。利用这一原理，成功地获得了新的超声图像。这些图像显示了金属样品的表面或表面下的弹性结构，即使它们的表面不是平坦的。同时，对超声相位共轭波的保真度进行了研究。采用纹影光学系统对相位共轭过程中不同阶段的超声场进行了可视化。超声成像结果表明，在我们的系统中，相位共轭波的波前形状与入射波的波前形状一致，误差小于一个波长。

This study is an attempt to improve ultrasonic C-mode imaging systems by using phase conjugate waves. An ultrasonic phase conjugator was devised making use of nonlinear piezoelectricity of PZT ceramics. This phase conjugator was built in an ultrasonic C-mode imager together with an waveguide. Since phase conjugate waves act as time reversed waves for arbitrary incoming waves, the initial ultrasonic field keeps its wavefront shape as if it is in a resonator. This effect provides ultrasonic images that are less sensitive to ultrasound's wavefront deformation but still sensitive to ultrasonic damping. With this principle, new ultrasonic images were successfully obtained. Those images showed surface or subsurface elastic structures of metal samples, even if their surfaces were not flat.At the same time, investigation of the fidelity of ultrasonic phase conjugate waves was carried out. The ultrasonic fields at several different stages in the process of phase conjugation were visualized by an schlieren optical system. The optical images of ultrasound revealed that, in our system, the shape of wavefronts of phase conjugate waves agreed with those of the incident waves with errors less than a wavelength.