Modeling of gradients in elastic properties for acoustic microscopy characterizations

In order to allow non-destructive characterizations by acoustic microscopy, the materials presenting in their properties a gradient perpendicular to t he surface are modelled. The method consists in regarding the material as b uilt of a succession of homogeneous layers numerous enough for the acoustic parameters to vary quasi-continuously. The gradient in Young modulus exist ing in the material is related to a gradient in acoustic properties measura ble by acoustic microscopy. The role of the shape of the gradient profile i s taken into account in the study of the convergence of the velocity of the surface mode V-S. The dispersion of the velocity V-S verses d/lambda (d is the depth of the gradient area and lambda is the wavelength) is studied as a function of the gradient profile. The shape of the curves shows that the best sensitivity to the profile is obtained for d/lambda approximate to 1.