Efficiency parameters in time reversal acoustics:: Applications to dispersive media and multimode wave propagation

This paper develops a theoretical background for the interpretation of the time reversal (TR) processes applied to the refocalization of acoustic waves in dispersive media with multimode propagation of waves. Two parameters are introduced in order to measure the efficiency of signal recompression in TR processes: spatial and temporal efficiencies. It is demonstrated that the signal recompression enhances when the medium is highly dispersive, when there are several modes involved in the process, and when the angular aperture of the TR mirror is appreciable. These results are applied to Lamb waves recompression in thin plates and focalization efficiencies in longitudinal and transversal directions are deduced. Finally, these theoretical results are compared with the experimental ones obtained for different plate thicknesses. (c) 2005 Acoustical Society of America.