Abstract

 

Low Frequency Emission by Nonlinear Interaction of Phase Conjugate Ultrasound Waves

Y.Pyl'nov (Moscow Institute of Radioengineering, Electronics and Automation, Moscow, Russia, and Institut d'Electronique et de Microelectronique du Nord (IEMN-DOAE-UMR CNRS 8520), Ecole Centrale de Lille, Villeneuve d'Ascq, France); P.Pernod (Institut d'Electronique et de Micro-electronique du Nord (IEMN-DOAE-UMR CNRS 8520), Ecole Centrale de Lille, Villeneuve d'Acsq, France); V.Preobrazhensky (Institut d'Electronique et de Micro-electronique du Nord (IEMN-DOAE-UMR CNRS 8520), Ecole Centrale de Lille, Villeneuve d'Acsq, France, and Wave Research Center of General Physics Institute RAS, Moscow, Russia)

e-mail: pylnov@yandex.ru

Low frequency emission (LFE) by means of parametric interaction of ultrasound beams is of interest for various applications in nonlinear acoustic imaging, elastography, vibro-acoustics etc. Interaction of waves can be distorted dramatically by phase aberrations when propagation medium is essentially inhomogeneous. The way to compensate phase distortions is to use the phenomenon of wave phase conjugation of acoustic beams of intensity high enough for manifestation of nonlinear effects. In the present paper, low combination frequency emission by means of nonlinear interaction of phase conjugate ultrasound beams is studied experimentally and theoretically. Phase conjugation effect is used for automatic overlap of interacting focused beams of frequencies 10MHz and 11MHz. Interaction of beams propagating in a homogeneous liquid and beams scattered by an object immersed in a liquid are considered. While variation of the object position for resonance interaction of co-directional waves does not affect on phase of the emitted wave of low frequency (difference frequency 1 MHz), the anomalous phase shift proportional to the sum of frequencies (21 MHz) is obtained for non-resonance interaction of contra-propagating waves. Application of anomalous phase shift for "supper resolution" in object positioning by means of nonlinear low frequency emission is discussed.

 

Section : 10