Effects of fluid-loading on Lamb mode spectra

Light fluid-loading of an infinite, isotropic, elastic plate nor only leads to the real modes of the unloaded plate acquiring a small, imaginary component, but also to the imaginary modes acquiring a small, real component. This provides a model with which computations of the leaky Lamb modes are seen to be compatible. The imaginary components of the propagating modes forma ''resonance pattern'' which contains all the information on the plate's transmittivity. The level of this pattern increases with the ratio of fluid to plate density. When the latter ratio is large enough tu cause the resonance pattern to overlap the peaks of the well-known imaginary semiloops, there is interaction leading to transition from the leaky Lamb mode behavior-tu that of a plate clamped on its surfaces with slip boundary conditions. Tl?ere is general agreement with the conclusions of S. I, Rokhlin er ni. [J. Acoust. Soc. Am. 85: 1074-1080 (1989)] and the present work broadens the parameter range over which those conclusions have been shown ro hold. (C) 1996 Acoustical Society of America.