This digest proposes a magnetic-core-based multi-MHz toroidal inductor structure, capable of achieving comparable quality factors to air-core inductors, while reducing its size significantly. Numerical optimization is performed to determine the optimal physical dimensions of the toroidal structure, resulting in a maximum inductor quality factor. Furthermore, the optimized magnetic-core toroidal inductor is compared with the optimized air-core toroidal inductor in terms of quality factor and size. An example 5.3 μH magnetic-core inductor designed at 13.56 MHz and 13 A peak ac current using the proposed optimization achieves a quality factor of ~1225, with an 8x volume reduction compared to an air-core toroidal inductor of the same quality factor. To validate the theoretical analysis, a 1-kW 13.56-MHz 12-cm air-gap capacitive WPT prototype is tested using magnetic-core toroidal inductors designed using the proposed structure. Experimental results are in good agreement with the theoretical findings.
