RECENT ADVANCES IN WAVES IN LAYERED MEDIA

Abstract

The topic of wave propagation in layered media has for a long time been of major interest in underwater and geophysical acoustics. Later on interest in this field arose due to needs in acousto-microelectronics, mainly surface acoustic wave devices, nondestructive evaluation of composite and layered materials and oil exploration. New applications have presented new challenging theoretical and experimental problems. One trend is to describe more complicated media including anisotropy, nonhomogeneity, imperfect interfaces, and wave diffraction on inhomogeneities ; a second trend is related to solutions of the inverse problem, in which properties of the media should be determined from the wave signature. In this paper we review recent developments in theoretical and experimental studies of elastic wave propagation in layered media with applications to ultrasonic evaluation of materials. We will focus mainly on anisotropy and media property reconstruction. We will also discuss the boundary conditioned for the imperfect interface, which may involve partial contact or other interface inhomogeneities. Such generalized boundary conditions can be systematically incorporated in the transfer matrix approach.