Enhancement of Thickness Measurement in Eddy Current Testing Using a Log–Log Method

• Published in: Journal of nondestructive evaluation Vol. 40; no. 2
• Main Authors: Xue, Zhian, Fan, Mengbao, Cao, Binghua, Wen, Dongdong
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.06.2021; Springer Nature B.V
• Subjects: Approximation; Characterization and Evaluation of Materials; Classical Mechanics; Control; Dynamical Systems; Eddy current testing; Eddy currents; Engineering; Linearity; Penetration depth; Phase shift; Solid Mechanics; Thickness measurement; Vibration; Log–log method; Tangent of phase angle; Eddy current testing; Thickness measurement
• ISSN: 0195-9298; 1573-4862
• DOI: 10.1007/s10921-021-00773-x

Eddy current testing for thickness measurement has great advantages, such as non-contact, low cost, and high efficiency. It is reported that there is a linear relationship between the tangent of the phase angle of impedance change and the thickness, termed as the approximate linear method (ALM). However, the accuracy of ALM is not very good, especially when the thickness of a specimen is very thin compared with standard penetration depth. The relationship between tangent of phase angle and thickness is simulated by Dodd-Deed model. The first and second derivatives of tangent of phase angle to thickness is consistent with the power function. Thus, the log–log method (LLM) is obtained by taking logarithm of power fitting equation. And, it is found that the change of excitation frequencies and lift-offs hardly affect the slope and linearity of LLM. The correctness and feasibility of LLM are verified by numerical simulation and experiments.