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Sensors 2017, 17(5), 943; doi:10.3390/s17050943

A Gradient-Field Pulsed Eddy Current Probe for Evaluation of Hidden Material Degradation in Conductive Structures Based on Lift-Off Invariance

1
State Key Laboratory for Strength and Vibration of Mechanical Structures, Shaanxi Engineering Research Center of NDT and Structural Integrity Evaluation, Xi’an Jiaotong University, Xi’an 710049, China
2
Leading Edge NDT Technology (LENDT) Group, Malaysian Nuclear Agency, 43000 Bangi, Kajang, Selangor, Malaysia
*
Author to whom correspondence should be addressed.
Academic Editors: Ashutosh Tiwari and Bharati Tudu
Received: 28 March 2017 / Revised: 17 April 2017 / Accepted: 22 April 2017 / Published: 25 April 2017
(This article belongs to the Special Issue Magnetic Sensors and Their Applications)
View Full-Text   |   Download PDF [2413 KB, uploaded 25 April 2017]   |  

Abstract

Coated conductive structures are widely adopted in such engineering fields as aerospace, nuclear energy, etc. The hostile and corrosive environment leaves in-service coated conductive structures vulnerable to Hidden Material Degradation (HMD) occurring under the protection coating. It is highly demanded that HMD can be non-intrusively assessed using non-destructive evaluation techniques. In light of the advantages of Gradient-field Pulsed Eddy Current technique (GPEC) over other non-destructive evaluation methods in corrosion evaluation, in this paper the GPEC probe for quantitative evaluation of HMD is intensively investigated. Closed-form expressions of GPEC responses to HMD are formulated via analytical modeling. The Lift-off Invariance (LOI) in GPEC signals, which makes the HMD evaluation immune to the variation in thickness of the protection coating, is introduced and analyzed through simulations involving HMD with variable depths and conductivities. A fast inverse method employing magnitude and time of the LOI point in GPEC signals for simultaneously evaluating the conductivity and thickness of HMD region is proposed, and subsequently verified by finite element modeling and experiments. It has been found from the results that along with the proposed inverse method the GPEC probe is applicable to evaluation of HMD in coated conductive structures without much loss in accuracy. View Full-Text
Keywords: electromagnetic non-destructive evaluation; gradient-field pulsed eddy current probe; lift-off invariance; material degradation; inversion; coated conductive structures electromagnetic non-destructive evaluation; gradient-field pulsed eddy current probe; lift-off invariance; material degradation; inversion; coated conductive structures
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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. (CC BY 4.0).

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Li, Y.; Jing, H.; Zainal Abidin, I.M.; Yan, B. A Gradient-Field Pulsed Eddy Current Probe for Evaluation of Hidden Material Degradation in Conductive Structures Based on Lift-Off Invariance. Sensors 2017, 17, 943.

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