EXCITATION OF GUIDED-WAVES IN GENERALLY ANISOTROPIC LAYERS USING FINITE SOURCES

The excitation of guided wave modes in generally anisotropic layers by finite sized strip sources placed on the surfaces of the layer is exa mined. The general problem of arbitrarily applied harmonic surface tra ctions is first solved using the normal mode expansion technique in co njunction with the complex reciprocity relation of elastodynamics. Thi s general solution is then specialized to loading situations modelling those commonly used to excite guided waves in layers for use in nonde structive evaluation. The amplitudes of the generated modes are writte n as the product of an ''excitation function'' which depends only on t he distribution of the applied tractions and an ''excitability functio n'' which depends only on the properties of the specific mode(s) being excited and which determines how receptive the modes are to the appli ed tractions. Expressions are obtained for the - 9 dB wave number and phase velocity bandwidths (sigma(beta) and sigma(nu), respectively) wh ich determine the widths of the wavenumber or phase velocity excitatio n spectra at the - 9 dB generation point. Finally, the problem of tran sient loading is addressed by superimposing time harmonic solutions vi a an integration over the dispersion curves of the layer.