Free Arrangement Wireless Power Transfer System with a Ferrite Transmission Medium and Geometry-Based Performance Improvement

Abstract

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.