We consider a finite element model for passive and active shielding of the magnetic stray field of induction heaters. In induction heaters, a metallic workpiece is heated by induced eddy currents. These currents are caused by a strong alternating magnetic field, generated by the excitation coil that surrounds the workpiece. First, an axisymmetric, quasi-static and time-harmonic numerical model of the induction heater is developed. The electrical currents are azimuthal. Next, passive shields are added, using impedance boundary conditions, relating the tangential components of the electric field E and the magnetic field H at the surface of the passive shield. Additionally, the possibility of active shielding is deepened. A number of extra coils is added to the finite element model. The currents in these compensation coils should generate counter fields. The best position and currents in the compensation coils are identified from a proper inverse problem. © 2003 Elsevier B.V. All rights reserved.
Sergeant, P., Dupré, L., Melkebeek, J., & Vandenbossche, L. (2004). Magnetic field computation for optimized shielding of induction heaters. Journal of Computational and Applied Mathematics, 168(1–2), 437–446. https://doi.org/10.1016/j.cam.2003.12.006