Surface Acoustic Wave-based Characterization of Randomly Distributed Surface Cracks

In this paper we present an approach to characterize surface breaking cracks by analayzing propagation of surface acoustic waves. We generate surface acoustic waves with plane wave fronts using a line-focused pulsed-laser to study scattering of SAWs on surface microcracks. A homogenized behavior of the randomly scattered and interferometrically detected field, i.e. the coherent waveform, is gained by spatially averaging the measurements. The data is studied in the time and frequency domain. The experimental results show the attenuation of the coherent SAWs due to scattering and the strongly distorted shape indicates the presence of dispersion. These parameters can be used to characterize the density and depth distribution of the cracks.