Wave phase conjugation of ultrasonic beams

This paper investigates the saturation mechanism of the nonstationary supercritical mode of parametric wave phase conjugation in a magnetostrictive medium. The numerical simulation considers the two most probable nonlinear mechanisms of interaction between elastic deformation and electromagnetic excitation. For the qualitative study of the dynamics of the system, a one-dimensional numerical simulation is sufficient if applied to an infinite medium with a finite active zone. The temporal form of the conjugate wave is obtained for both hypotheses. Comparison with experiments shows that only one mechanism corresponds to the experimental behavior.

Section: Introductionmentioning

confidence: 99%

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

Merlen¹,

Preobrazhensky

Pernod

2002

“…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.…”

Section: Introductionmentioning

confidence: 98%

Time-reversed sound beams of finite amplitude

Cunningham

Hamilton

Brysev

et al. 2001

Numerical simulations based on the nonlinear parabolic wave equation are used to investigate time reversal of sound beams radiated by unfocused and focused sources. Emphasis is placed on nonlinear propagation distortion in the time-reversed beam, and specifically its effect on field reconstruction. Distortion of this kind, due to amplification during time reversal, has been observed in recent experiments [A. P. Brysev et al., Acoust. Phys. 44, 641-650 (1998)]. Effects of diffraction introduced by time-reversal mirrors with finite apertures are also considered. It is shown that even in the presence of shock formation, the ability of time reversal to retarget most of the energy on the source or focal region of the incident beam is quite robust.

“…A good review of the WPC development can be found in Ref. 11. Of course this presentation of WPC would not be complete without mentioning the technique of the multichannel transmitting receiving antenna arrays 12 which is extremely efficient in operating frequency under 10 MHz but where time reversal is obtained by a numerical process and not by a physical effect.…”

Section: Introductionmentioning

confidence: 98%

Resonant solutions in wave phase conjugation induced by a limited magnetoacoustic conjugator

Merlen¹,

Zhang²

2006

This paper presents, in one dimension, the general analytical solution of the acoustic phase conjugation in an active medium in contact with passive media of arbitrary impedance. The homogeneous case where no impedance jumps exist at the edge of the active zone is obtained as a particular case. This homogeneous case was the only one treated explicitly in the literature but mostly in the frame of Brillouin scattering. In contrast to this previous work, the present theory is based on a preliminary straightforward analysis using a dual-time-scale method and provides very practical results like the threshold of the supercritical modes, the rate of amplification, and its link with the stress repartition in the conjugator.