Impulse Modeling of the Rayleigh Wave Propagation Generated by a Spherical Focused Transducer

In order to characterize materials locally by means of the Rayleight wave analysis, a new modeling of acoustic microscopy in the case of an impulse excitation is presented. The usualV(z) representation established for a given frequency component, is extended to the case of a broadband excitation of the transducer. Therefore, the time-dependant acoustic response of the material,s(z,t), is mainly composed of two echoes: the specular and the Rayleigh contributions which are resolved in time. In the first part, we demonstrate that the acoustic response can be represented by the time convolution product between the acoustic signal detected at the focus on an ideal reflector, and a function depending onz andt variables. This last function is connected to the tranducer emission profile, which includes the diffraction effects, and the reflectance of the material. In the second part, the modeling is discussed with regard to experimental data on several materials and takes into account the attenuation phenomena. Experimental results and computations are shown to be in a good agreement.