Minimization of vias in PCB implementations of planar coils with litz-wire structure

PCB implementation of planar windings replicates the structure of conventional litz wires in order to reduce the ac losses. This structure consists of a set of fine trace electrically connected in parallel which are transposed by means of changes of both trajectory and layer. An appropriate transposition strategy is essential to reduce the winding ac losses, however PCBs with high number of vias could result expensive and not reliable. Taking advantage of the field profile of planar windings, in this work is studied the minimization of the number of vias without significant reduction of performance. The work is carried out by means of a combination of finite-element analysis (FEA) simulations and experimental verification on ultra-thin (0.3 mm) PCB prototypes of planar inductors oriented to a domestic induction heating application.