The reflection of the Lamb wave in a semi-infinite plate

The Lamb wave technique is used in the detection of internal defects inplates.The reflection of the Lamb wave at the free edge of the plate has been shownto be rather complicated.The reflected wave is usually composed of infinite numberof Lamb wave modes even in the case of incidence of one pure mode.The analysisof the reflection problem is complicated in nature as the orthogonality relations ofthe eigen modes of the Lamb wave concern both the stresses and displacements.Weadopt the principle of the least squares as a new approach to simplify the analysis,inwhich the eigen-modes are taken as the trial function.It seems to be simple and effective.In most cases a good enough result can be obtained on using an 8-bitmicrocomputer.Here the coefficients of the various reflected modes are calculated,some interesting phenomena on the mode conversion are indicated and the condi-tions on the pure mode reflection are given.