Optimization procedure of complex permeability for a wireless power transfer system

Wireless power transfer (WPT) is fundamentally based on Faraday´s law of induction and uses relatively strong magnetic field to transfer the required power from the source to the load without any electrical contact. To reduce the leakage magnetic field and enhance the magnetic coupling between the coils, soft magnetic material such as ferrite is frequently used. However, it is hard to determine the optimum magnetic properties to meet the various design requirements such as the cost, the efficiency and the regulations for the time-varying electromagnetic field (EMF) exposure. In this paper, we present the procedure to find the optimum complex permeability satisfying the following design requirements: the transfer efficiency of 90% and the minimum levels of EMF around the coils. The results show that solely maximizing the real part of complex permeability or minimizing the magnetic loss tangent is unsuitable to meet the given design requirements for the WPT system.