Active and passive magnetic shielding for stray field reduction of an induction heater with axial flux

A combined active and passive shield is designed for an industrial axisymmetric induction heater for steel wire. Both the active and the passive shield should reduce the magnetic stray field of the induction heater in a given area, namely the target area. They should have low electromagnetic losses and cause a limited change of the heating induced in the workpiece. The positions as well as the currents of the active shield coils and the position and length of the passive shield are optimised. The numerical models are verified by comparing the results with measurements on the unshielded induction heater. Several passive shields (steel, copper and ferrite) and active shields are studied, resulting in a maximal field reduction of 43 dB.