High Q-factor compact coils having non-uniform wire width for wireless power transfer system

Compact coil is designed at 6.78 MHz for wireless power transfer (WPT) system. The proposed coil is optimized by adjusting the gap between wires, scaling factor, and the number of turns to achieve high quality factor (Q-factor), and its Q-factor is 263. The Q-factor of the proposed coil exhibits 1.21 times higher than conventional coil. The coil is made on thin substrate with a low relative permittivity and a loss tangent to decrease influence of the substrate, and the coil size is 100 mm × 100 mm × 0.4 mm. The measured efficiency is shown as 95% at 50 mm and 30% at 200 mm. The compact coil having non-uniform wire width has higher efficiency than that of conventional coil. The proposed coil can be utilized for the various mobile applications.