Eliminating backwall effects in the phased array imaging of near backwall defects

Abstract

Ultrasonic array imaging is widely used to provide high quality defect detection and characterization. However, the current imaging techniques are poor at detecting and characterizing defects near a surface facing the array, as the signal scattered from the defect and the strong reflection from the planar backwall will overlap in both time and frequency domains, masking the presence of the defect. To address this problem, this paper explores imaging algorithms and relevant methods to eliminate the strong artefacts caused by the backwall reflection. The half-skip total focusing method (HSTFM), the factorization method (FM) and the time domain sampling method (TDSM) are chosen as the imaging algorithms used in this paper. Then, three methods, referred to as full matrix capture (FMC) subtraction, weighting function filtering, and the truncation method, are developed to eliminate or filter the effects caused by the strong backwall reflection. These methods can be applied easily with few tuning parameters or little prior knowledge. The performances of the proposed imaging techniques are validated in both simulation and experiments, and the results show the effectiveness of the developed methods to eliminate the artefacts caused by the backwall reflections when imaging near backwall defects.

Model-Based Parametric Study of Surface-Breaking Defect Characterization Using Half-Skip Total Focusing Method

“…This is due to some phase difference between the raw and extracted backwall reflection signal so that the subtraction cannot make the most effect. Besides, there is another disadvantage of FMC subtraction [22] that the pairs with larger lateral separations, e.g., the first element as transmitter and the last as receiver, will have less averaging effect according to Eq. ( 8).…”

“…Another idea that avoids counting backwall reflection signal into the process of HSTFM image reconstruction is to introduce a weight function [22], which is based on the angle between incident and receiving direction of wave. However, this method is invalid when the Snell's law-based wave mode conversion introduced in Sect.…”

Ultrasonic Image Artifacts Removing Technique Based on SoS Kernel

“…Moreover, Potter [14] et al proposed a technique to reduce the artifacts using a hybrid full matrix formed through a temporally weighted sum of coherent and reconstructed matrices. In addition, Huthwaite [15] proposed a method combined with weighting function filtering and the truncation imaging algorithm to eliminate the artifacts, and Budyn [16] adopted a statistical robustness geometry mid-value to replace the delay-superposition imaging algorithm for suppressing the artifacts. In 2019, Guanru [17] generated a phase reversal signal to counteract the signal tail.…”