Improved Performance of a Flat-Wire Coil With Magnetic Composite Material for Wireless Power Transfer

Abstract

This letter focuses on improvements in the performance of flat-wire coils for wireless power transfer in smartphones based on the Qi interface standard. At high frequencies, alternating-current copper losses increase due to the proximity and skin effects. A low-permeability magnetic composite with low hysteresis loss was applied to a coil to reduce coil losses. A parametric analysis was used to obtain the optimum composition of the magnetic coating. Power transmission experiments on a coated coil designed for minimum loss showed that the steady-state temperature was lower than that of an uncoated coil. The coated-coil resistance was lower at high frequencies, where resistance due to skin and proximity effects are significant. When misaligned with respect to a charging pad's transmit coil, the coated coil had a smaller decrease in efficiency compared to an uncoated coil.