Turning the tides - 33 Years of Professor Brian Morton

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Experimental verification of the theory of multilayered Rayleigh waves

A phenomenon which has been termed "multilayered Rayleigh modes" has been presented in previous papers. This study aims to prove experimentally the existence of these waves in anisotropic periodically multilayered media. These modes result from a combination of Floquet waves which propagate in a periodically multilayered medium when all the Floquet waves are inhomogeneous. The experimental verification was done using an acousto-optic technique and a measurement of the reflected field, which was obtained with a hydrophone measurement system, on a carbon/epoxy composite plate. The experimental and calculated dispersion curves of the multilayered Rayleigh modes were then drawn. The coincidence of the curves was found quite good, thus confirming our theory. However, two modes were found by the acousto-optic technique not to fit into the theory. One experimentally detected mode was found to correspond to the Lamb mode of the plate and the other was not experimentally detected by the acousto-optic technique. Measurement of the reflected field for this mode, which was obtained with a hydrophone measurement system, and its comparison with the predicted reflected field make it possible to verify the existence of the mode. The combination of both experiments permit a good coincidence to be found. (C) 1999 American Institute of Physics. [S0021-8979(99)01314-6].status: publishe