Abstract (Invited)

Nonlinear Effects Associated with Generation and Propagation of Phase Conjugate Ultrasound Beams

L.M.Krutyansky (Wave Research Center of the General Physics Institute RAS, Moscow, Russia); M.F.Hamilton (Department of Mechanical Engineering, the University of Texas at Austin, Austin, TX, USA)

e-mail: krut@orc.ru

Nonlinear acoustical effects in phase conjugate (PC) ultrasound beams have recently become a promising topic for study and applications. One of the most effective methods of phase conjugation utilizes parametric magnetoacoustic interaction in magnetostrictive ceramics. Here we review the corresponding studies of nonlinear phenomena associated with generation and propagation of intense PC waves. Experimental investigations of PC waves under conditions of nonlinear saturation of the pump signal are described. Mode competition in the parametric interaction is demonstrated using two identical beams incident simultaneously on the conjugator. Numerical estimates of performance quality are provided for both linear and nonlinear modes of operation. Nonlinear propagation effects in finite-amplitude PC beams in water are considered experimentally and numerically. Even with strong waveform distortion, field reproduction is quite accurate when the aperture of the conjugator is sufficiently large. Conjugation of the second harmonic in a focused nonlinear incident beam was also studied. The conjugate wave reproduces fairly well the incident harmonic component in the focal region. Automatic focusing of a nonlinear conjugate beam through a pseudo-random phase layer is demonstrated. The focusing through the layer results from phase locking of the harmonics. Underlying principles for nonlinear applications are summarized.

Section : 10