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Metal defects sizing and detection under thick coating using microwave NDT

Lookup NU author(s): Hong Zhang, Dr Bin Gao, Professor Gui Yun TianORCiD, Dr Wai Lok Woo, Dr Libing Bai


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An experimental study to evaluate shapes and sizes of defect under thick coating by microwaves NOT is demonstrated. Specially fabricated thick fire protect coated steel panels with embedded defects are inspected using an X-band (8.2-12.4 GHz) open-ended rectangular waveguide. The fundamental idea behind using this probe is presented along with several experimental results to validate this method for defect detection under coating. The reflected signal related to the phase and magnitude of the reflection coefficient at the waveguide aperture is used to create images of these coated samples under test. These images indicate the ability of microwaves for identifying and sizing defects under thick coating layer. Linear sweep technique is used here to obtain multiple frequency spectrum variances. Principle Component Analysis (PCA) algorithms have been employed to enhance the resolution of our proposed method. A series of performance comparison with PCA algorithms are also provided to extract the defect features from thick coating layer influence. To evaluate the proposed technique, steel with known defect and five coated steel plates with unknown defect under different coating thickness are measured. Results indicate that the defect detection capability has been enhanced with the suitable use of signal processing methods. (C) 2013 Elsevier Ltd. All rights reserved.

Publication metadata

Author(s): Zhang H, Gao B, Tian GY, Woo WL, Bai LB

Publication type: Article

Publication status: Published

Journal: NDT & E International

Year: 2013

Volume: 60

Pages: 52-61

Print publication date: 01/12/2013

Online publication date: 20/07/2013

Acceptance date: 05/07/2013

ISSN (print): 0963-8695

ISSN (electronic): 1879-1174

Publisher: Elsevier


DOI: 10.1016/j.ndteint.2013.07.002


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