A 3D resonant wireless charger for a wearable device and a mobile phone

A resonant wireless power transfer (WPT) system that allows for free positioning of a wearable device about a 360° axis of rotation and simultaneous charging of a mobile phone is proposed. A 3D transmitter coil structure is introduced to provide a cylindrical charging surface with a uniform magnetic field. A prototype charging system including an amplifier and a rectifier operating at 6.78 MHz is demonstrated. The prototype delivers 1 W to a wearable device and 5 W to a mobile phone simultaneously with a power transfer efficiency of 48%.