Guided ultrasonic wave phase and group velocity measurement

In the context of Structural Health Monitoring (SHM), guided waves can be used for the efficient inspection and monitoring of large, thin-walled structures. This enables monitoring systems employing a limited number of permanently installed sensors. However, the propagation of guided waves is complicated due to the existence of dispersion and multiple wave modes. Accurate knowledge of the guided wave propagation characteristics, such as the frequency dependent phase and group velocity is required to achieve good sensitivity for defect detection and for prediction of scattering characteristics. The influence of different measurement configurations on the accuracy of phase and group velocity quantification was evaluated. The accuracy of sensor placement and signal-to-noise ratio (SNR) were found to influence measurement repeatability and methods to reduce these effects were applied. For low frequency guided wave propagation in an isotropic plate (A₀ Lamb mode), good repeatability and agreement of experimentally measured velocities with theoretical predictions based on nominal material properties was achieved.