Evaluation of coating thickness using lift-off insensitivity of eddy current sensor

Meng, X., Lu, M., Yin, W., Bennecer, A. and Kirk, K. (2021) Evaluation of coating thickness using lift-off insensitivity of eddy current sensor. Sensors (Switzerland). 21(2) 1424-8220.

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2021_Meng_Xiaobai_etal_MDPI_Evaluation_of_Coating_Thickness_Using_Lift-Off_Insensitivity_of_Eddy_Current_Sensor
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Abstract:

Defect detection in ferromagnetic substrates is often hampered by nonmagnetic coating thickness variation when using conventional eddy current testing technique. The lift-off distance between the sample and the sensor is one of the main obstacles for the thickness measurement of nonmagnetic coatings on ferromagnetic substrates when using the eddy current testing technique. Based on the eddy current thin-skin effect and the lift-off insensitive inductance (LII), a simplified iterative algorithm is proposed for reducing the lift-off variation effect using a multifrequency sensor. Compared to the previous techniques on compensating the lift-off error (e.g., the lift-off point of intersection) while retrieving the thickness, the simplified inductance algorithms avoid the computation burden of integration, which are used as embedded algorithms for the online retrieval of lift-offs via each frequency channel. The LII is determined by the dimension and geometry of the sensor, thus eliminating the need for empirical calibration. The method is validated by means of experimental measurements of the inductance of coatings with different materials and thicknesses on ferrous substrates (dual-phase alloy). The error of the calculated coating thickness has been controlled to within 3% for an extended lift-off range of up to 10 mm.

Uncontrolled Keywords:

Multi-frequency eddy current, multi-layer conductor, non-destructive testing, coating thickness, lift-off inversion

Creators:

Meng, X., Lu, M., Yin, W., Bennecer, A. and Kirk, K.

Faculties, Divisions and Institutes:

Faculties > Faculty of Arts, Science & Technology > Engineering

Date:

9 January 2021

Date Type:

Publication

Journal or Publication Title:

Sensors (Switzerland)

Volume:

Number:

Number of Pages:

Language:

English

DOI:

10.3390/s21020419

ISSN:

1424-8220

Status:

Published / Disseminated

Refereed:

Yes

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