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International Society for Industrial Process Tomography

3rd World Congress on Industrial Process Tomography

The Use of Inductance Spectroscopy to Image the Conductivity Distribution of a Layered Conductor


W Yin, S J Dickinson and A J Peyton


Engineering Department, Lancaster University, Lancaster, LA1 4YR, UK, w.yin@lancaster.ac.uk


ABSTRACT


This paper presents an inverse method for determining the conductivity distribution of a flat, layered conductor using a multi-frequency electromagnetic sensor. Eddy current sensors are used in a wide range of non-destructive testing (NDT) applications. Single frequency sensors are very common, however, the potential of an eddy current sensor with spectroscopic techniques offer the ability to extract depth profiles and examine more fully the internal structure of the test piece. In this paper, the forward solution for a small right-cylindrical air-cored coil placed next to a layered conductor is based on the analytic solution provided by the transfer matrix approach. For inverse solution, a modified Newton-Raphson method was used to adjust the conductivity profile to fit a set of multi-frequency inductance in a least-squared sense. The approximate Jacobian matrix (sensitivity matrix) was obtained by the perturbation method. Numerical results of the forward solution are provided for cases of step, continuous conductivity profiles. Good estimates for the conductivity profile were obtained. Experimental eddy-current tests are performed by taking the difference in inductance of the coil when placed next to a reference conductor and next to a layered conductor over the range 1k-1MHz. Inverse results based on experimental and simulated data verified this method.


Keywords Multi-frequency electromagnetic sensor, conductivity distribution, layered conductor

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