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A free arrangement wireless power transfer system with a ferrite transmission medium and geometry-based performance improvement method are introduced here. The proposed system addresses the efficiency collapse caused by misalignment or increased distance between the transmitter and receiver coils, that is, receivers can be located anywhere on the plate-shaped system, which can be applied to a table, wall, or floor to supply electrical power as needed. Despite its high cost, ferrite is advantageous over air as a medium as the latter diminishes the efficiency at a distance or misalignment. Further, ferrite reduces the transmitter volume and number of coil turns, which is useful for practical applications. Skewed-shape coil windings with higher effective mutual inductance than unskewed structures are used in this system to increase power transfer efficiency. The improvements from the ferrite and coil-winding geometry are verified through Ansoft Maxwell v14.0 and MATLAB simulations. Four prototypes of the proposed system are fabricated and validated at 100 kHz. The highest transfer efficiency at the farthest distance, 55 cm, is 17.5% with the 4-cm-skewed ferrite structure, whereas no power is delivered beyond 10 cm in air. Consequently, the proposed system achieves wider power transfer area and better efficiency without additional power and coil windings while the system complies with the guidelines provided by International Commission on Non-ionizing Radiation Protection (ICNIRP) and IEEE for human safety. This article is accompanied by a demonstrating video.

This paper presents the system of wireless power transfer (WPT) in a planar structure with various ways to increase both average value and uniformity in the efficiency of the proposed system. The horizontal flux approach is selected to implement the proposed system, taking advantage of optimization, compared to the system with the vertical flux approach. To overcome the limitation of the approach and enhance the performance, the following three methods are introduced. The permeability of the transmission medium, which is related to the transfer efficiency, is increased by using ferrite. Also, winding multiple transmitter coils is presented to improve uniformity. Finally, adjusting the structure of the transmitter coils raises the intensity of the net magnetic field. By a combination of these methods, average efficiency is observed as 81.3% with low standard deviation, indicating the system has uniformly high transfer efficiency all over the plate. Consequently, the proposed system demonstrates the feasibility of the WPT system in which the receiver can be located freely.