High Power Density Self-Resonant Coupler for Flexible Surface Wireless Power Transfer System With Nanocrystalline Ribbon

Self-resonant wireless power transfer (WPT) gains industrial attention for its high power density due to eliminating additional capacitors in the compensation network. While current research predominantly focuses on low-power applications in the megahertz range for antenna and microwave applications, the significant potential of WPT systems at medium power levels with resonant frequencies below 100 kHz is often overlooked. This study explores self-resonant WPT systems, focusing on medium power levels with low resonant frequency. A four-layer capacitor-free coil pad is introduced, utilizing a flexible printed circuit (FPC) with polyimide substrates. Meanwhile, nanocrystalline flake ribbon (NFR) cores are explored since their merits of high magnetic saturation and low core loss surpass traditional MnZn ferrites. Electromagnetic simulation confirm reduced magnetic flux leakage, underscoring the efficacy of NFR cores and capacitor-free FPC coil pads in medium-power WPT systems for flexible surface charging applications. The experimental results showcase a high power density of 29.9 W/cm
³
and a high efficiency of 92% at the low self-resonant frequency of 56.7 kHz, demonstrating consistent performance across both flat and curved surfaces with a transmission distance of 45 mm.