Thin self-resonant structures with a high-Q for wireless power transfer

The range, efficiency, and size of resonant coils in an inductive wireless charging system is determined by the quality factor Q of the resonant coils. The multi-layer self-resonant structure is a new resonant coil technology that has been demonstrated to have a Q 6× larger than conventional coils. However, to date, implementations of this structure have been thick, which limits their practical applications. In this paper, we explore the relationship between the thickness of a self-resonant structure and its performance. A computationally efficient 2-D optimization algorithm is proposed to design thin resonant structures and illustrate the trade-offs in the design. A new magnetic core shape is proposed which shapes the magnetic field lines to be parallel to the conductive layers and reduces current crowding. Finally, a prototype 3.5 mm thick self-resonant structure is constructed, which has a measured quality factor of 560 despite having a diameter of only 6.6 cm; this provides a 3.03× improvement over the state-of-the-art wireless power transfer coils in the literature.