Swept-frequency eddy current testing to characterize a nonmagnetic metallic plate and a nonconductive coating over it

Abstract

In the measurement of a metallic plate’s dimension by eddy current testing, the plate’s electrical conductivity is required but practically unavailable. This study investigated the application of swept-frequency eddy current testing (SFECT) to measure the thicknesses of the plate and a nonconductive coating over it, even without knowing the plate’s conductivity. Hinted by the known analytical expressions available for the calculation of the impedance of an air-cored coil above a plate, we found that the maximum phase angle of the normalized SFECT signal is relevant to the thickness of a conductive plate and the liftoff, regardless of the conductivity, and can be applied to thickness measurement. Analytical and experimental studies also showed that the conductivity of a nonmagnetic plate can be measured nondestructively by using SFECT signals in the high frequency range.

Keywords

Swept-frequency eddy current testing nonmagnetic conductivity thickness coating layer

Get full access to this article

View all access options for this article.

References

Mcmaster

R.C.

Mclntire

and Mester

M.L.

, Nondestructive Testing Handbook, 2nd edn, American Society of Nondestructive Testing, 1986.

Cheng

, Thickness measurement of metal plates using swept-frequency eddy current testing and impedance normalization, IEEE Sensors Journal 17(14) (2017), 4558–4569, doi:10.1109/JSEN.2017.2710356.

Dodd

C.V.

and Deeds

W.E.

, Analytical solution to eddy current probe-coil problem, J. Appl. Physics. 39(6) (1968), 2829–2839.

Theodoulidis

T.P.

and Kriezis

E.E.

, Eddy Current Canonical Problems (With Applications to Nondestructive Evaluation), 1st edn, Tech Science Press, USA, 2006.

User’s Manual of IM3536 LCR Meter (in Japanese), 2nd edn, HIOKI, Sep. 2016.

Wang

H.B.

and Feng

Z.H.

, Noncontact thickness measurement of metal films using eddy-current sensors immune to distance variation, IEEE Trans. Instrum. Meas. 64(9) (2015), 2557–2564.

Yin

and Peyton

A.J.

, Thickness measurement of metallic plates with an electromagnetic sensor using phase signature analysis, IEEE Trans. Instrum. Meas. 57(8) (2008), 1803–1807.

User’s Manual of Loresta-GP, MCT-TP600 (in Japanese), Mitsubishi Chemistry Ltd.

Harrison

D.J.

Jones

L.D.

and Burke

S.K.

, Benchmark problems for defect size and shape determination in eddy-current nondestructive evaluation, J. Nondestructive Evaluation 15(1) (1996), 21–34.