Effective Magnetization and Forces due to Eddy Currents

A simple method is presented to evaluate the effective magnetization due to eddy currents excited by ac magnetic fields in finite conductive objects. The values of magnetization enable the estimation of the forces exerted on the object by the effect of eddy currents. The main method relies on assuming a similarity between eddy current magnetization and the magnetization due to diamagnetic effects, which is easier to evaluate. The validity of the present method is checked by comparing results regarding the eddy current forces with data obtained from conventional but much more complicated methods or from experimental data. The eddy current forces can be of value in the production of pure metals, in eddy current driven actuators or in the construction of electromagnetically levitated vehicles. Furthermore, it seems that the present approach may be useful in order to evaluate the eddy current losses in finite conductive objects excited by ac magnetic fields, e.g., in inductive heating, or eddy current nondestructive testing, or to evaluate the influence of small conductive objects on ac excitation coils, e.g., eddy current metal detection. The method described here is based on combining techniques which are on one hand related to the conventional evaluation of eddy currents in certain one-dimensional geometries. On the other hand, the evaluation is derived by approximating a behavior of the ac magnetic field in finite objects (especially the demagnetization effect is treated in this way) in a way similar to that followed when the magnetic forces acting on a diamagnetic object are calculated.