Application of time-reversal focusing in elastic wave propagation to buried object detection

Abstract

Time-reversal focusing is a technique for focusing energy both spatially and temporally to a single desired point. First studied in fluid media, additional studies have demonstrated the applicability of time-reversal focusing to solid media and elastic wave propagation. A significant difference between time-reversal and other focusing methods is time-reversal focusings immunity to the variation of wave speeds and the effects of scattering objects within the medium. In the detection of buried objects, this feature is paramount where wave speed variations and clutter are common in the region to be searched. The effectiveness of time-reversal focusing is investigated for a variety of configurations of scattering objects. Fields of uniform objects are examined as well as distributions of randomly shaped clutter, and changes in the propagation medium. Both experimental and three-dimensional numerical results are presented. In previous studies, a phenomenon of super-resolution caused by high-order scattering has been observed where focusing exceeds the diffraction limits of the excitation array. The extent of super-resolution is evaluated for the various configurations of scattering objects in an elastic medium. [Work supported by ARO.]