Analysis of Coil-Thickness-Variation Technique for Q-Factor Enhancement of Rectangular Planar Coils

For wireless power transfer (WPT) applications, such as battery charging, the attainment of a high coil quality factor ( $Q$ ) becomes prudent to ensure a high-power transfer efficiency (PTE). In this article, we demonstrate an effective method to enhance $Q$ by employing different thicknesses for each trace of the coil. The thickness of the inner turns of the coil, where high alternating current (ac) losses are concentrated, is relatively smaller compared to the outer coil turns. This technique realizes a reduction in the ohmic resistance, thereby increasing $Q$ of the coil. Furthermore, we present the analysis on the performance of the conventional coils with the same turn thicknesses compared to the proposed coil. To validate this technique, the prototypes of both the proposed and conventional coil structures are fabricated, where good agreement is achieved between the simulation and measurement results. The proposed coil realizes an increment of about 11.54% in $Q$ compared to the conventional coil.