A Novel Phase-Control-Based Energy Beamforming Techniques in Nonradiative Wireless Power Transfer

Recent efforts to increase the energy transfer efficiency in magnetic resonant coupling-based wireless power transfer (WPT) systems, have been focused on improving quality factor, precision of impedance matching, and position alignment between the resonators. Although those approaches are effective to increase transfer efficiencies, the transferred energy can easily be wasted due to leakage flux of nondirectional fields. In this paper, we present a novel magnetic field shaping technology for improving the energy efficiency in a near-field WPT system. In this study, the beamforming techniques that have been used for radio frequency systems are efficiently exploited in a WPT system to improve the transfer efficiencies by minimizing unnecessary leakage flux. The optimal antenna structure for energy forming is first determined through mathematical analysis. Using the proposed crossed antennas, the phase-control method is effectively used to form magnetic fields in particular directions. The proposed energy forming-based WPT system using crossed antennas is implemented with the phase control of three-power stack transmitters. The experimental results matches well with the theoretical analysis, and the energy-forming approach for synthesizing the magnetic fields achieves average improvements of the transfer efficiency and transfer distance of up to 20.1% and 30%, respectively, over the conventional nonradiative energy transfer approach at 1 m distance.