Lamb mode conversion in a plate with a delamination

A theoretical study of Lamb mode propagation through a part of a plate containing a finite-length, delamination parallel with the surface is presented. In the delamination boundary region, which is taken parallel with the free plate surface, noncontact boundary conditions are assumed. The calculation is based on a modal decomposition method. As a result of diffraction on a delamination the incident Lamb mode is efficiently converted into Lamb modes with wave numbers close to the wave number of incident mode. The transmission coefficient of a Rayleigh wave incident on a delamination located near the surface has an oscillating dependence on the delamination parameters and has a pronounced minimum where there is a strong conversion into transmitted Lamb modes. Inversely, using the method of phase conjugation, a proper incident Lamb mode combination can be efficiently converted into a single transmitted Lamb or Rayleigh wave. (C) 2004 Acoustical Society of America.