SCATTERING OF ULTRASOUND (INCLUDING RAYLEIGH WAVES) BY SURFACE ROUGHNESS AND BY SINGLE SURFACE FLAWS. A REVIEW OF THE WORK DONE AT PARIS 7 UNIVERSITY

Since some years our team has worked on the characterization of rough surfaces f~om a study of the angular and frequency dependence of the backscattered intensity of ultrasonic waves. We shall discuss, in view of our experimental results, the different components of the signature of the surface profile which can be evaluated by these means:-r.m.s. roughness h with a precision of the order of 1 ~m in the range 6-100 ~m,-influence of the autocorrelation distance L,-when present, surface periodicities with a precision which can be better than 1%. In the case of quasiperiodic surfaces, we shall present a comparison between the spectra theoretically predicted in the low-frequency approximation for various samples, and the ultrasonic spectra actually observed. Since 1977, we have also used Rayleigh waves to study surface propPrties and surface cracks in ceramics and metals and we shall give an introduction to the results obtained at the oresent time. This tooic will be developed by B.R. Tittmann in a following paper