Journal of Nondestructive Evaluation

, Volume 14, Issue 1, pp 39–46 | Cite as

Rapid inversion of eddy current data for conductivity and thickness of metal coatings

  • Ananth Sethuraman
  • James H. Rose


A feature-based method that determines the thickness and electrical conductivity of a coating on a metal plate from the change in the frequency-dependent impedance of an eddy-current probe coil is presented. Recently a least-squares solution of this problem was presented, which, however, requires approximately 20 CPU minutes on a DEC 5000 work station for the analysis of each set of measurements. We show that a feature-based approach can reduce the time to a few seconds on the same processor. We start by showing that a three-parameter scaling of the resistive component of the impedance change vs. frequency leads to a simple and nearly universal curve. Consequently these parameters provide a simple and compact way of expressing the data. Next, we show that the three scaling parameters can be used to construct a look-up table that determines the conductivity and thickness of the coating. Finally, we test the method using experimental data.

Key words

Scaling feature-based inversion eddy-currents thickness conductivity 


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  1. 1.
    J. C. Moulder, E. Uzal, and J. H. Rose, Thickness and conductivity of metallic layers from eddy current measurements,Rev. Sci. Instr. 63(6):3455–3465 (1992).Google Scholar
  2. 2.
    D. H. S. Cheng, The reflected impedance of a circular coil in the proximity of a semi-infinite medium,I.E.E.E Trans. Instr. Meas. 14(3):107–116 (1965).Google Scholar
  3. 3.
    C. V. Dodd and W. E. Deeds, Analytical solutions to eddy-current probe-coil problems,J. Appl. Phys. 39(6):2829–2838 (1968).Google Scholar
  4. 4.
    O. Baltzersen, Model-based inversion of plate thickness and liftoff from eddy current probe coil measurements,Mater. Eval. 51(1):72–76 (1993).Google Scholar
  5. 5.
    J. R. Bowler and S. J. Norton, Eddy current inversion for layered conductors,Res. Nondestr. Eval. 4:205.Google Scholar
  6. 6.
    E. Uzal, J. C. Moulder, S. Mitra, and J. H. Rose, The impedance of coils over layered metals with continuously variable conductivity and permeability: Theory and experiment,J. Appl. Phys. 74(3):2076–2089 (1993).Google Scholar
  7. 7.
    J. H. Rose and S. M. Nair, Exact recovery of the DC electrical conductivity of a layered solid,Inverse Problems 7:L31 (1991).Google Scholar
  8. 8.
    S. J. Norton, A. H. Kahn, and M. L. Mester,Res. Nondestr. Eval. 1:167 (1989).Google Scholar

Copyright information

© Plenum Publishing Corporation 1995

Authors and Affiliations

  • Ananth Sethuraman
    • 1
  • James H. Rose
    • 1
  1. 1.Center for Nondestructive EvaluationIowa State UniversityAmes

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