Reconfigurable transmitter coil structure for highly efficient and misalignment-insensitive wireless power transfer systems in megahertz range

The structural optimization of coils is a key issue in wireless power transfer (WPT) applications owing to size limitations. In this study, a novel planar-spiral transmitter coil (TX-coil) with an outer-tight and inner-sparse configuration is proposed to achieve a high quality factor (Q-factor) and uniform magnetic field, which ensures high efficiency and improves the misalignment tolerance for several-megahertz WPT systems. Furthermore, a closed-form expression for the Q-factor is provided and analyzed for coil optimization. By using this method, a TX-coil with an outer diameter of 100 mm and a wire diameter of 1.5 mm is designed and tested at 1 MHz. Finite element method simulations and experimental results demonstrate that the Q-factor is increased by about 8% in comparison with evenly spaced planar spiral coils, which is achieved while ensuring a relatively uniform magnetic field.