PREDICTION OF THE IMPULSE-RESPONSE OF MATERIALS USING A SAM TECHNIQUEIN THE MHZ FREQUENCY-RANGE WITH A LENSLESS CYLINDRICAL-FOCUSED TRANSDUCER

This paper deals with a new approach to the theoretical prediction of the impulse response of materials achieved by a special surface acoust ic microscope operating in the MHz frequency range. The modeling is ba sed on developments in the harmonic regime, and is extended to the cas e of a broad-band excitation. The real emission profile of the transdu cer (pupil function) is taken into account in the modeling, associated with the corresponding diffraction effects. This is applied to a lens less transducer with a line focus (cylindrical shape) in order to char acterize anisotropic materials. A one dimensional (1D) modeling is dev eloped and then validated by comparison between experiments and theore tical predictions for three materials: glass, ceramic and polished ste el. The modeling well predicts the absolute time shape and amplitude o f the acoustic response of the material. By means of an optimization t echnique, this modeling tends to solve the inverse problem of the elas tic constant evaluation, the ultrasonic attenuation measurement relate d to the grain size or the velocity gradient estimation through the sa mple thickness. (C) 1998 Elsevier Science B.V.