Some didactical and some practical remarks on free plate waves

Abstract

It is recalled how wave equations can be generated from dispersion relations. The bending wave equation for thin plates including some higher-order terms is obtained by this general method and compared to the corresponding equation of Timoshenko. Further, the dispersion of free plate waves is derived in a concise and elementary manner without using a scalar potential and a vector potential for the displacements. Finally, as a matter of practical interest, exact and approximate expressions for the ratio of parallel to perpendicular displacements at a plate surface are calculated. Under favourable circumstances measurement of this ratio allows decomposing an observed wave into its quasi-longitudinal and bending components.