Prediction of transient eddy current fields using surface impedance methods

Surface impedance methods are used primarily in steady-state eddy current problems where the thickness of the conductor is much larger than the skin depth. This application is extended to transient problems involving shell structures. The shell structure examined is a three-dimensional spherical shell. At time t=0, a uniform z -directed field of 1 T is turned on. Attention is primarily focused on extracting eigenvalues using the surface impedance method and more specifically on how to build the temporal responses from these eigenvalues. Because the source chosen is a unit step, it is necessary to incorporate a host of eigenvalues to get a good initial transient prediction. A less costly alternative is to relax the requirement of how much of the field is excluded from the conductor and to use fewer eigenvalues