The thesis deals with the scattering of plane longitudinal elastic waves incident normally on a cylindrical cavity in a solid medium. The scattered fields are solved with consideration of attenuation effects of the medium by introducing complex wavenumbers. The addition theorem of the cylindrical functions is employed in order to evaluated those functions with complex arguments. Angular distributions and impulse response curves of the scattered waves are obtained at various receiver positions. Characteristics of the impulse response curves are explained by means of ray theory. From these results, it is found that the impulse responses are composed of the two waves reflected and diffracted by the cavity. To verify the accuracy of predicted impulse responses, experiments are carried out for aluminium and acryl specimens as a typical non-attenuating medium and attenuating one, respectively. The spectral ratio method is used to obtain the attenuation coefficients of acryl. It is observed that the measured attenuation coefficients increase with frequency linearly. Experimental results are in good agreements with predicted scattered waves. Therefore, once the input waveform and the attenuation coefficients of a medium are known, it is possible to predict the waveforms of scattered waves due to a cylindrical cavity. In addition, a method to detect the position of a cavity is suggested. From the fact that the time intervals in the impulse responses are related to the path length difference of the ray scattered by a cavity, an objective function is defined and the absolute position of a receiver is determined by minimizing this function. The suggested method is verified by simulation and experiment, and good results are observed. It is expected that the techniques in this study can be applicable to the fields of geophysics and non-destructive testings.
