High resolution defect imaging in guided waves inspections by dispersion compensation and nonlinear data fusion

Performance of defect imaging procedures based on scattered guided waves (GW) acquired by a network of piezoelectric sensors relies mainly on the density of transducers adopted as well as on the accuracy in the time of flight (ToF) estimation. The dispersive and multimodal nature of GW makes this latter task complicated. In this work, a strategy to achieve high resolution defect imaging is proposed and tested to image cracks on an aluminum plate. In particular, first dispersion compensation and basis pursuit schemes are exploited to accurately extract the GW ToF information from the acquired dispersive signals and to translate it into distance of propagation (DoP). Next, the DoP is used to feed four beamforming techniques namely (i) delay and sum, (ii), weighted coherence-factor, (iii) channel rank and (iv) Capon beamformer, which outputs are finally integrated by a proposed nonlinear data-fusion technique. A quantitative comparison on experimental Lamb waves waveforms acquired with a Scanning Laser Doppler Vibrometer (SLDV) on a damaged aluminum plate shows the high resolution imaging performance of the proposed method.