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The Lift-Off Effect in Eddy Currents on Thickness Modeling and Measurement

Kral, J. ; Šmid, R. ; Ramos, H. ; Ribeiro, A. L.

IEEE Transactions on Instrumentation and Measurement Vol. 62, Nº 7, pp. 2043 - 3047, July, 2013.

ISSN (print): 0018-9456
ISSN (online): 1557-9662

Journal Impact Factor: 1,790 (in 2014)

Digital Object Identifier: 10.1109/TIM.2013.2247713

Abstract
This paper uses a linear transformer model to investigate the effect of the lift-off on the results of the thickness measurement of non-ferromagnetic metallic plates. The transformer model previews that the time derivative of magnetization curves obtained for different gaps between the excitation coil and the plate should intercept in a single point when low magnetic coupling factors are considered. To assess the validity of the model results are compared with experimental data obtained with a giant magnetoresistive (GMR) sensor probe. For comparison, the sensor output voltage time derivative must be performed as well. The model results are confirmed by actual measurement results.