Experimental determination of the near-surface conductivity profiles of metals from electromagnetic induction (eddy current) measurements

Autor: John C. Moulder, Erol Uzal, James H. Rose
Rok vydání: 1994
Předmět:
Zdroj: Inverse Problems. 10:753-764
ISSN: 1361-6420
0266-5611
Popis: We report experimental measurements that test an inverse method for determining the electrical properties of conducting surface layers on metals. We test the method's ability to determine the spatial variation of the near-surface electrical conductivity of flat, layered (one-dimensional) metal plates from experimental measurements of the frequency-dependent impedance of a small right-cylindrical air-core coil placed next to the metal surface and driven by an alternating current. This is an inverse problem for the diffusion equation with complex wavevector. We fit the experimental measurements to a recent closed-form analytic solution for the impedance of a conductivity profile that varies as a constant plus a hyperbolic tangent with depth into the sample. The model profile depends on three parameters, which roughly correspond to: (1) the thickness of the surface layer, (2) the change in conductivity and (3) the sharpness of the transition from surface to bulk conductivity. Data were obtained by measuring the impedance of an air-core coil for flat Cu and Ti plates that have surface layers that extend to various depths. We extended the range of the study by using simulated data, which were obtained by solving the forward problem numerically. Good estimates for the 'average' conductivity profile were obtained when the conductivity was maximum (minimum) at the surface and decreased (increased) monotonically to the bulk conductivity as a function of depth into the sample. The thickness, conductivity change and the sharpness of the profile were successfully inferred from experiment in most cases.
Databáze: OpenAIRE
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