Analysis and Evaluation of Air-core Two-coil Wireless Power Transfer System Configurations

This paper presents the analysis and evaluation results of different air-core two-coil wireless power transfer (WPT) configurations to achieve maximum power transfer efficiency for the frequency range below 1 MHz. Simplified two-port network circuit model based on experimentally measured parameters is used to evaluate the different two-coil configurations for short range power transmission. The configuration design of the wireless coils impacts the energy transfer efficiency of the WPT system. Three different WPT coils configurations for air-core WPT systems are compared based on the scattering parameters. Different two-coil configurations are obtained from several combinations of flat spiral coils and helical coils. The results show that the flat spiral coil pair configuration achieves a power transfer efficiency of ~68% without ferrite when the coil pairs are well aligned. However, its efficiency decreases rapidly when the misalignment increased. On the other hand, the presented configuration of one helical coil inside another larger helical coil achieves higher power transmission efficiency of ~72% without ferrite. It is also easier to be aligned and maintain alignment compared with the flat spiral coil pair.