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Methods of Controlling Lift - off in Conductivity Invariance Phenomenon for Eddy Current Testing

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posted on 01.06.2020 by Zhongwen Jin, Yuwei Meng, Rongdong Yu, Ruochen Huang, Mingyang Lu, Hanyang Xu, Xiaobai Meng, Qian Zhao, zhijie zhang, anthony peyton, wuliang yin

Previously, a conductivity invariance phenomena (CIP) has been discovered – at a certain lift-off, the inductance change of the sensor due to a test sample is immune to conductivity variations, i.e. the inductance – lift-off curve passes through a common point at a certain lift-off, termed as conductivity invariance lift-off. However, this conductivity invariance lift-off is fixed for a particular sensor setup, which is not convenient for various sample conditions. In this paper, we propose using two parameters in the coil design – the horizontal and vertical distances between the transmitter and the receiver to control the conductivity invariance lift-off. The relationship between these two parameters and the conductivity invariance lift-off is investigated by simulation and experiments and it has been found that there is an approximate linear relationship between these two parameters and the conductivity invariance lift-off. This is useful for applications where the measurements have restrictions on lift-off, e.g. uneven coating thickness which limits the range of the lift-off of probe during the measurements. Therefore, based on this relationship, it can be easier to adjust the configuration of the probe for a better inspection of the test samples.


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Submitting Author's Institution

University of Manchester

Submitting Author's Country

United Kingdom