Improving Wireless Power Transfer Efficiency Using Hollow Windings With Track-Width-Ratio

With the widespread growth of slim portable electronics, research into planar spiral windings for wireless power transfer (WPT) battery charging systems has gained a lot of attention due to their low profile, reproducibility, and manufacturability. The major design goal for windings in WPT systems is high-quality factor (Q) for a given inductance. This study presents a new method to improve Q by using a nonunity track-width-ratio (TWR) geometrical arrangement in conjunction with increasing the inner radius of winding to make an improved hollow planar spiral winding. The inductance regulation of this technique combined with its exceptional improvements in Q make it a superior choice for resonant WPT systems. Inductance and resistance models are provided in order to assess the Q improvement. A 5-W, 110-200-kHz WPT system was built and tested based on the wireless power consortium Qi standard to confirm the advantages of the improved windings on the transmission efficiency of the system. An increase from 70% to 90% are observed from employing the proposed winding technique designed using the provided models.