Interaction of Lamb waves with a grating composed of two spatial periodicities: Study in dual space

This work is a contribution to the characterisation of a rough surface by ultrasonic methods. The target application is the non-destructive evaluation of interfaces (corrosion or bonding quality). Usually, rough surfaces exhibit a limited number of dominant spatial periodicities. This paper deals with the propagation of Lamb waves in a plate with a finite surface grating composed of two spatial periodicities. Conversion modes of Lamb waves are shown. Normal displacements of the plate are studied using Fourier analysis. A new quantitative link between these data and the power spectral density (PSD) of the profile is highlighted. An experimental study confirms the numerical predictions.