Localization of defects in irregular waveguides by dispersion compensation and pulse compression

Abstract

In this work a pulse-echo procedure suitable to locate defect-induced reflections in irregular waveguides is proposed. In particular, the procedure extracts the distance of propagation of a guided wave scattered from a defect within the echo signal, revealing thus the source-defect distance. To such purpose, first, a Warped Frequency Transform (WFT) is used to compensate the signal from the dispersion of the guided wave due to the traveled distance in a portion of the waveguide that is assumed as reference. Next, a pulse compression procedure is applied to remove the additional dispersion introduced by the remaining irregular portion of the waveguide.Thanks to this processing the actual distance traveled by the wave in the regular portion of the irregular waveguide is revealed. Thus the proposed strategy extends pulse-echo defect localization procedures based on guided waves to irregular waveguides. Since the processing is based on Fast Fourier Transforms, the algorithm can be easily implemented in real time applications for structural health monitoring. The potential of the procedure is numerically demonstrated by processing Lamb waves propagating in an irregular waveguide composed by aluminum plates with different thicknesses and tapered portions.

Increased range of ultrasonic guided wave testing of overhead transmission line cables using dispersion compensation

“…To correct for this, the theoretical dispersion curves were scaled by dividing them by the length ratio given in Eq. (7). The theoretical group velocities for the cable were, therefore, calculated using…”

“…Hall and Michaels performed adaptive dispersion compensation to improve imaging of defects on an aluminium plate using a distributed transducer array [13]. De Marchi et al used a warped frequency transform to provide dispersion compensation for an irregular waveguide [7]. Zeng and Lin proposed a chirp-based dispersion pre-compe nsation technique using a priori knowledge of the propagation distance [30].…”

Optimizing the Calibration Error of Refraction Angles in Ultrasonic Angle Beam Testing

“…For example, F. Bettayeb suppressed noise to enhance flaw location by wavelet transform [9]; C. Zhou developed the probability-based diagnostic imaging approach to improve the accuracy [10]; L. Gandossi, J. He and J. Yang used Bayesian updating to improve accuracy [7,11,12]; J. Zhang used the scattering-matrix-based approach to increase sensitivity in ultrasonic arrays testing [13]; L. De Marchi used the warped frequency transform technology to overcome the difficulties associated with wave arrival time detection [14,15]. J.…”

Pulse-compression based iterative time-of-flight extraction of dispersed Ultrasonic Guided Waves

“…However, in order to implement the WDR technique the propagation distance should be known. In one of the latest studies, Marchi et al extended WFT based dispersion compensation to irregular wave guides [19], and then combined it with pulse compression to localize defects [20]. However, only triangular pulse excitation is used and no experimental validation is presented.…”