Efficiency dependence on wire type for wireless power transfer of magnetic resonant coupling

Wireless power transfer is expected to be applied to portable devices and electric automobiles in future, and it requires high efficiency and the miniaturization of coils. To improve the efficiency of wireless power transfer, the authors propose the use of a litz wire (LMW) with a magnetoplated wire (MPW), which is a copper wire plated with a thin Fe film. The transmission efficiency using coils with a solid copper wire (COW), a litz wire with a copper wire (LCW) and an LMW are measured. The frequency is 13.56 MHz, the inner diameter of the coils is 36 mm, their number of turns is 8 and the transmission distance is 36 mm. Results show that efficiencies of the COW, LCW and LMW coils in output power is 1 W are 63.9%, 52.8% and 69.6%, respectively, and the efficiency of the LMW coil is the highest. Also, the axial direction length of the LMW coil is half that of the COW for the same efficiency.