Advertisement

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
Article

Abstract

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 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  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

Personalised recommendations