Impact of Encapsulation on the Core Loss of Ferrites in Inductive Power Transfer

Inductive power transfer (IPT) magnetics are often “potted” with an encapsulant material to improve thermal performance. Mismatched thermal expansion of the encapsulation and magnetic core materials creates a residual mechanical stress that permanently reduces the magnetic performance of the Mn-Zn ferrite core layer. An encapsulated small-scale Double-D IPT pad designed for 2.5kW is built and tested, and the core loss of the ferrite tiles increases by 121% after encapsulation with a polyurethane-based material. The change in the core loss of the potted IPT pad after encapsulation is predicted using finite element analysis, and the proposed method matches within 7.3%. Three methods are presented to mitigate this increase in losses and experimentally verified on ferrite toroids. These results show that the choice of encapsulation material significantly impacts the thermal, structural, and electromagnetic behavior of the IPT pad.