Passive and active electromagnetic shielding of induction heaters

In induction heaters, a metallic workpiece is heated by eddy currents, induced by strong alternating magnetic fields. Using numerical models, proper active and passive shields are designed in order to mitigate the stray field of the induction heater. Two models are presented: an axisymmetric finite-element (FEM) and a hybrid finite-element-boundary-element (FEM-BEM) model. Results of both numerical methods are compared and verified with measurements on an induction heater archetype. A good correspondence is observed. Combination of passive and active shielding results in almost 20-dB field reduction.