Prediction of the impulse response of materials using a SAM technique in the MHz frequency range with a lensless cylindrical-focused transducer

Abstract

This paper deals with a new approach to the theoretical prediction of the impulse response of materials achieved by a special surface acoustic microscope operating in the MHz frequency range. The modeling is based on developments in the harmonic regime, and is extended to the case of a broad-band excitation. The real emission profile of the transducer (pupil function) is taken into account in the modeling, associated with the corresponding diffraction effects. This is applied to a lensless transducer with a line focus (cylindrical shape) in order to characterize anisotropic materials. A one dimensional (1D) modeling is developed and then validated by comparison between experiments and theoretical predictions for three materials: glass, ceramic and polished steel. The modeling well predicts the absolute time shape and amplitude of the acoustic response of the material. By means of an optimization technique, this modeling tends to solve the inverse problem of the elastic constant evaluation, the ultrasonic attenuation measurement related to the grain size or the velocity gradient estimation through the sample thickness.