Ultrasonic phase conjugate waves-generation, visualization, and applications

The phase conjugate waves of ultrasound were generated with PZT ceramics through the nonlinear piezoelectric interaction between elastic field of incident ultrasound at ω and electric field applied at 2 ω. The intensity reflectivity of the phase conjugator was shown to be as high as 100% for the incidence at 10 MHz. Mechanism of the phase conjugation was discussed in relation with modulation in the ultrasonic velocity given by the electric field to the PZT material. The stroboscopic schlieren technique was used to visualize their behavior in water: the slow-motion video visually confirmed the time-reversal property. The phase conjugator was installed in a system of scanning acoustic imaging. The image reconstructed of the phase conjugate reflection yielded clear figures of the targets put within an irregularly shaped lump of agarose gel that distorted the wave front. Usefulness of the phase conjugation phenomenon applied to the ultrasonic imaging was shown