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Journal of Sensors
Volume 2018 (2018), Article ID 9545832, 8 pages
https://doi.org/10.1155/2018/9545832
Research Article

Multiframe Ultrasonic TOFD Weld Inspection Imaging Based on Wavelet Transform and Image Registration

1Photoelectric Engineering Institute, Southwest Jiaotong University, Chengdu 610031, China
2Southwest Jiaotong University NDT Research Center & Olympus NDT Joint Laboratory of Nondestructive Testing, Chengdu 610031, China

Correspondence should be addressed to Lin Luo

Received 30 May 2017; Revised 14 November 2017; Accepted 3 December 2017; Published 13 February 2018

Academic Editor: Jaime Lloret

Copyright © 2018 Jiaxu Duan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

TOFD (time of flight diffraction) is a kind of weld defect detection technology by using ultrasonic diffraction wave signal. Because the diffraction intensity is far less than ultrasonic echo wave intensity, thus, the noise contained in TOFD signal is fairly large, and the formed image is not clear enough. Therefore, it is difficult to determine the size of defects accurately. In this paper, a method of noise reduction of TOFD signal and improving the resolution of the image are discussed based on the combination of wavelet thresholding and image registration. Wavelet multiresolution analysis method is adopted and the A-scan signal is decomposed into different frequency components. We propose a new threshold function to process the wavelet coefficients, which guarantees to denoise while preserving the useful information as much as possible. Setting up the ultrasonic TOFD inspection system and the image data with randomly distributed noise can be obtained via fine shake of the probes during testing. Then, image registration based on maximum correlation and blending is adopted to eliminate the noise in further step. The result shows that the proposed method can achieve denoising, together with resolution enhancement.