Abstract
Generation of intense, phase-conjugated ultrasonic beams by a single active magnetic element in a supercritical parametric mode has been demonstrated experimentally and theoretically. Specifically, phase conjugation with amplification greater than 80 dB, producing intensities of several hundred W/cm2 at MHz frequencies, is accomplished via parametric electromagnetic pumping of magnetoelastic solids. Reversal of the sound field incident on the conjugator has been confirmed by observation of the self-targeting of beams on scattering sites in water [Usp. Fiz. Nauk 168, 877–890 (1998) (in Russian)]. The large amplification provided by the conjugator leads to nonlinear distortion and shock formation in the conjugate field. These nonlinear effects are studied experimentally with measurements based on light diffraction for conjugated beams in water having intensities of 2 W/cm2 and frequencies near 5 MHz. Numerical simulations corresponding to experimental conditions take into account absorption, diffraction, nonlinearity, and the finite size of the conjugator. The simulations reveal the presence of shocks, yet accurate reversal of the incident field despite the strong waveform distortion [Phys. Acoust. (in press (1998)]. Potential applications of this technololgy are discussed. [Work supported by RFBR (Grants 96-02-17301, 98-02-16761), CRDF (Project RE1-270), and ONR.]
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