Planar reactive shield for wireless power transfer system of mobile device

Abstract

Recently, the demand and interest in wireless power transfer (WPT) have been rapidly increased. In particular, a wireless charging system of the mobile device is excepted to grow rapidly in the future. For the high power transfer efficiency and long-distance, the WPT system use the high frequency. As the frequency of the WPT system high, the affects toward human body of other electronic devices are increased. Therefore, a reduction method for the leakage magnetic field generated from the wireless charging mobile device must be considered. To reduce the leakage magnetic field from the WPT system, the several methods such as metallic shield, magnetic shield, active shield, reactive shield are introduced. The reactive shield is most suitable for suppressing the leakage magnetic field from the wireless charging mobile device among various shields. In this thesis, an effective and compact reactive shield to reduce the magnetic field leakage from a planar wireless power transfer (WPT) coil for mobile electronics devices is proposed. The proposed resonant reactive shielding coil consists of loop conductor and a resonant capacitor which generate a cancelling magnetic field to reduce the magnetic field leakage from the WPT coils. As the cancelling magnetic field is generated from the WPT coils and consumes negligible power. The mechanism and the design methodologies to control cancelling magnetic field using the inductance and capacitance of the shielding coil are explained. The shielding performance and power transfer efficiency are compared to that of a conventional shield. A 3D simulation has been performed to verify the performance of the shielding coils. The experimental validation with fabricated test vehicle showed good correlation with the simulation and the confirmed the effective shielding without significant change in the WPT efficiency.