Excitation of plane Lamb wave in plate-like structures under applied surface loading

Lamb waves play an important role in structure health monitoring (SHM) systems. The
excitation of Lamb waves has been discussed for a long time with absorbing results. However,
little effort has been made towards the precise characterization of Lamb wave excitation by
various transducer models with mathematical foundation. In this paper, the excitation of plane
Lamb waves with plane strain assumption in isotropic plate structures under applied surface
loading is solved with the Hamiltonian system. The response of the Lamb modes excited by
applied loading is expressed analytically. The effect of applied loading is divided into the
product of two parts as the effect of direction and the effect of distribution, which can be changed
by selecting different types of transducer and the corresponding transducer configurations. The
direction of loading determines the corresponding displacement of each mode. The effect of
applied loading on the in-plane and normal directions depends on the in-plane and normal
displacements at the surface respectively. The effect of the surface loading distribution on the
Lamb mode amplitudes is mainly reflected by amplitude versus frequency or wavenumber. The
frequencies at which the maxima and minima of the S0 or A0 mode response occur depend on
the distribution of surface loading. The numerical results of simulations conducted on an infinite
aluminum plate verify the theoretical prediction of not only the direction but also the distribution
of applied loading. A pure S0 or A0 mode can be excited by selecting the appropriate direction
and distribution at the corresponding frequency.