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Published online by Cambridge University Press: 15 June 1999
In order to allow non-destructive characterizations by acoustic microscopy, the materials presenting in their properties a gradient perpendicular to the surface are modelled. The method consists in regarding the material as built of a succession of homogeneous layers numerous enough for the acoustic parameters to varyquasi-continuously. The gradient in Young modulus existing in the material is relatedto a gradient in acoustic properties measurable by acoustic microscopy. The role ofthe shape of the gradient profile is taken into account in the study of theconvergence of the velocity of the surface mode V S. The dispersion of thevelocity V Sversusd/λ (d is the depth of the gradient areaand λ is the wavelength) is studied as a function of the gradient profile. Theshape of the curves shows that the best sensitivity to the profile is obtained ford/λ≈1.