Acoustic phase conjugation by nonlinear piezoelectricity. II. Visualization and application to imaging systems

Abstract

Phase conjugate waves of ultrasound were generated in PZT ceramics through nonlinear piezoelectric interaction between an incident ultrasonic field at ω and an electric field at 2ω. The amplitude reflectivity of the phase conjugator was 23% at 10 MHz. The behavior of the incident waves and the phase conjugate waves were visualized by stroboscopic schlieren technique. Time-reversal property and the automatic correction of wavefront distortion in the phase conjugate process were confirmed. A scanning ultrasonic imaging system with a PZT phase conjugator has been built. This system was used to visualize test samples composed of solid plates and phase disturbers. Images by phase conjugate reflection yielded clear figures of the solid plates in spite of the existence of phase disturbers made of agarose gel with rough surfaces, whereas conventional images showed serious distortion.

Supercritical parametric phase conjugation of ultrasound. Numerical simulation of nonlinear and nonstationary mode

“…10 Applications of parametric WPC are discussed extensively. 11,12 The general problem of supercritical WPC has no analytical solution. Recently a numerical technique based on Godunovtype procedure was elaborated for description of WPC supercritical dynamics and was demonstrated on an example of a linear WPC mode at the given pumping field approximation.…”

Supercritical parametric wave phase conjugation as an instrument for narrowband analysis in ultrasonic harmonic imaging

“…A fundamental feature of the conjugate wave is to reconstruct the field of an incident wave, including compensation of phase distortions occurring during the wave propagation. This specificity has been demonstrated using an example of scanning acoustic microscope with piezoceramic and magneto-elastic phase conjugators (MPC) [7], [8]. The MPC allows for operation in a supercritical parametric mode, providing giant amplification of the conjugate wave (80 dB and more) [5].…”

Time-reversed sound beams of finite amplitude

“…Phase conjugation was developed first in optics ͑a review is given, e.g., in the book by Zel'dovich et al 3 ͒ and subsequently introduced in acoustics by Bunkin et al 4 The most effective physical mechanisms for acoustic phase conjugation involve parametric modulation of the sound speed in solids through application of electromagnetic fields. [5][6][7][8] These and other methods of acoustic phase conjugation are reviewed by Brysev et al 6 and Ohno et al 7 In principle, perfect reproduction of the incident field by the time-reversed field may be accomplished when the following conditions are met: the mirror is a surface that encloses the source of radiation; the medium is lossless; and inhomogeneous properties of the medium do not vary with time. Although nonlinear propagation does not, by itself, prevent exact field reproduction, it does when amplification is introduced during time reversal, or when shocks are formed and therefore losses occur in either the incident or timereversed fields.…”