An improved beamforming technique for increased imaging resolution in GW-based SHM

Structural Health Monitoring (SHM) of 2D areas can be performed bycombining time waveforms acquired by an array of Guided Wave (GW) transducersthrough phased addition algorithms. However, spatial resolution in defectlocalization is often limited by both dispersion in wave mode propagation andimaging noise associated to conventional delay-and-sum (DAS) beamforming.Starting from a statistical interpretation of DAS, this paper combines arecently proposed time-frequency procedure based on the Warped FrequencyTransform (WFT) and convex optimization with an adaptive thresholding techniqueto process multi-mode and dispersive Lamb waves. The proposed signal processingis applied to time waveforms recorded at an array of scan points after waveguideexcitation. The results show high-resolution source and scatterer imaging, thusconsiderably improving localization accuracy by imaging noise removal.