Ultrasonic surface wave parameters monitoring using 3D vibrometry and ellipsometry for local material characterization

Rayleigh wave is widely used in non-destructive testing and evaluation, the three-dimensional vibrations inspection highlights the bivariate nature of these waves and their elliptic motion. The links between this motion and the material properties are well established, however, theoretical expressions are very sensitive to the measurement errors and the purity of the surface wave. If the classical processing often uses independently the two components of the wave, it seems more complete to process the two components together using the adequate bivariant filters. This work presents the monitoring of the 3D propagation of ultrasonic Rayleigh waves and the signal processing dedicated to the identification of their characteristic parameters. It is particularly focused on the wave ellipticity, i.e. the horizontal to vertical component ratio (H/V-ratio). This phenomenon is studied analytically, numerically and experimentally. Over a scanned area, the local mechanical parameters are estimated using time signals extracted from each single point. The obtained results for Aluminum show a good agreement between the analytical, numerical and experimental studies of Rayleigh wave ellipticity. Moreover, these H/V ratios are consistent with the theoretical values found in literature. This method is also applied on simulation data to study orthotropic materials (wood/bone), obtaining promising results.