Analysis of the coupling between small ring-type coils used in adaptable-size burners for domestic induction heating hobs

Domestic induction hobs with adaptable-size burners are under development in order to improve the flexibility of the apparatus by adapting the active area to the size of the vessel. Such burners are implemented by means of several small ring-type closely-arranged coils, each one of them supplied by a resonant inverter. Its activation depends on the size and the shape of the pot. The basic winding is a ring-type circular small coil, whose self impedance was reported in the past. In this paper, the coupling between coils in terms of impedance is derived. Coils are modeled as axisymmetric current density distributions with parallel revolution axes. Analytical expressions to calculate mutual impedance for several coils placed between two linear semi-infinite media are derived. Experimental measurements have been performed to validate the results.