Flexible and efficient 6.78MHz wireless charging for metal-cased mobile devices using controlled resonance power architecture

Wireless charging to mobile devices with metal cases has been plagued with poor efficiency (∼ 40%) and low power capability with traditional magnetic resonance (MR) technology. This paper will present a controlled resonance technology to use the metal case to enhance the coupling between the RX and TX windings, and to count for the inductance and coupling changes by modulating the resonance in RX and TX resonators and keeping the system in optimal operation mode automatically. In typical smart phone and smart watch applications, about 70% system efficiency is now achieved while the benefit of some spatial freedom is still maintained.