Wireless-Power-Transfer Planar Spiral Winding Design Applying Track Width Ratio

With the increase of wireless power transfer (WPT) systems for home and industrial electronic applications, planar spiral winding design techniques are gaining attention due to their low profile, reproducibility, and manufacturability. The major design goal for windings in WPT systems is a high quality factor (Q) for a given inductance. This paper establishes a new method to improve and analyze Q by using a nonunity track-width-ratio geometrical arrangement. The results are applicable for a variety of planar spiral winding families and make full use of the ability to change the width of the traces to improve Q for wireless powered applications. In order to simplify the analysis and provide generality, a unified dimensional system framework is also proposed, covering the racetrack geometry and its derivatives-circular, rectangular, generalized octagonal, and traditional racetrack windings. The resulting dimensional system provides an accurate geometrical description of the windings to obtain high Q and a simple set of manufacturing specifications. Details and derivations of this new method to calculate inductance, dc resistance, and ac resistance estimation to obtain improved Q are presented. A comprehensive set of experimental measurements confirms the validity of the dimensional system and the improvements in Q for wireless powered applications.