Rapid inversion of eddy current data for conductivity and thickness of metal coatings
- 181 Downloads
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 wordsScaling feature-based inversion eddy-currents thickness conductivity
Unable to display preview. Download preview PDF.
- 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.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.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.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.J. R. Bowler and S. J. Norton, Eddy current inversion for layered conductors,Res. Nondestr. Eval. 4:205.Google Scholar
- 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.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.S. J. Norton, A. H. Kahn, and M. L. Mester,Res. Nondestr. Eval. 1:167 (1989).Google Scholar