This paper presents the modeling and optimization of a High-frequency self-resonant planar coil for wireless power transfer (WPT) to improve the power transfer efficiency by maximizing the coil’s quality factor (Q). While self-resonant planar coils using two coils for internal capacitance offer design flexibility for high-power operation, achieving a high Q-value remains challenging due to significant magnetic losses at MHz frequencies. To address this, we developed a gradient–based optimization method that uses an equivalent circuit model, derived from Archimedean spiral equations for inductance, capacitance, and series resistance, to avoid extensive parameter sweeps. Incorporating multiple physical constraints, we employed sequential least squares programming (SLSQP) in Python to maximize the Q factor under equality and inequality constraints, reducing optimization time significantly. A prototype copper-sheet planar coil, tested at 13.56 MHz, achieved Q > 700, and with a Class Phi-2 inverter at 400 W over 12.2 cm, demonstrated 96% coil-to-coil efficiency, confirming the effectiveness of the proposed design.
