TRANSIENT EDDY-CURRENT ANALYSIS FOR GENERALIZED STRUCTURES USING SURFACE IMPEDANCES AND THE FAST FOURIER-TRANSFORM

Surface impedances have been utilized in eddy current problems, primarily where the skin depth is small compared to the conductor thickness being modeled. In this paper, we extend their use to arbitrary thickness conductors. In addition, we investigate modeling different shapes as combinations of slabs. In particular, a cylinder is emulated as a polygon of slabs to verify the versatility of the technique. The application to sinusoidal steady-state problems is straightforward. Of greater interest is the extension to the transient problem. A solution is sought via the fast Fourier transform. It is generally considered that the use of transform methods is inefficient by comparison to a Crank-Nicholson scheme because of the overhead involved in the generation of each frequency solution. However, with the surface impedance method, the calculation of each frequency solution is fast; the overhead required in setting up the problem, albeit the integral or finite element matrix, is geometry dependent only, and need be performed but once. The calculation of the transient response of a cylinder placed in an exponentially decaying field is computed and compared to analytic results. Some discussion is given to the benefits of breaking up the excitation field into parts that start and end at the same level. © 1990 IEEE