Analysis of inductive coupling coils for extending distances of efficient wireless power transmission

This paper proposed an approach to extend the transmission distances of wireless power transmission (WPT) systems under the constraint of the coil size and optimized delivered power and efficiency. Based on the reflected load theory, the inductive coupling coils can be modelled as an equivalent circuit for simple analysis and be extended to multiple-coil wireless power transmission systems. According to this proposed approach, power transmission efficiency (PTE), power delivered to load (PDL), and geometric factors of the coil are taken into consideration simultaneously as the proposed figure-of-merit (FoM) to optimize the performance of the wireless power transmission systems. Finally, a practical 4-coil WPT was implemented to verify the theory, and based on the FoM, the most efficient design parameters of WPT were identified. The optimal distance was increased by 50%, and the PTE remains more than 78%.