Scanning imaging system with ultrasonic phase conjugator

The phase conjugate waves of ultrasound were generated with PZT ceramics through the nonlinear piezoelectric interaction between elastic field of incident ultrasound at /spl omega/ and electric field applied at 2/spl omega/. The amplitude reflectivity of the phase conjugation was shown to be as high as 30% for incidence at 10 MHz. The stroboscopic schlieren technique was used to visualize their behavior in water: the slow-motion video visually confirmed their time-reversal property. The phase conjugator of PZT was installed in a system of scanning acoustic imaging. A metal plate with letter-shaped holes as a target was put in an artificial disturber of sound waves and imaged. Normal images were also taken without the phase conjugator for comparison, which were seriously distorted and superimposed on a ghost due to the disturber. The image reconstructed of the phase conjugate reflection yielded clear figure of the targets in spite of the disturber. The usefulness of the phase conjugation phenomenon applied to the ultrasonic imaging was shown.