A dispersion compensation procedure to extend pulse-echo defects location to irregular waveguides

A time–frequency signal processing procedure aimed at extending pulse-echo defect detection methods based on guided waves to irregular waveguides is proposed. In particular, the procedure returns the distance traveled by a guided wave that has propagated along a waveguide composed by segments with different dispersive properties by processing the detected echo signal. To such aim, the acquired signal is processed by means of a two-step procedure. First, a warped frequency transform (WFT) is used to compensate the dispersion of the guided wave due to the traveled distance in a portion of the waveguide that is assumed as reference. Next, a further compensation is applied to remove from the warped signal the group delay introduced by the remaining irregular portion of the waveguide. Thanks to this processing strategy, the actual distance traveled by the wave in the regular portion of the irregular waveguide is revealed. Thus, the proposed procedure is suitable for automatically locate defect-induced reflections in irregular waveguides and can be easily implemented in real applications for structural health monitoring purposes. The potential of the procedure is demonstrated and validated numerically by simulating and processing Lamb waves propagating in waveguides made up of different uniform, tapered and curved segments.