An NFC-Connected Coupler using IPT-CPT-Combined Wireless Charging for Metal-Cover Smartphone Applications

A near field communication (NFC)-connected coupler using inductive power transfer (IPT)-capacitive power transfer (CPT)-combined wireless charging is proposed for metal-cover smartphone applications. To mitigate eddy current loss in the metal cover, CPT is introduced. Compared with traditional CPT, wireless power transfer through a metal cover is realized, and cost and valuable space inside the smartphone are saved. To achieve CPT through a metal cover, the metal cover itself is separated by a cross slot and utilized as receiving plates. To reduce the voltage across the metal cover within a safety range, IPT is applied. The already-existing NFC antenna is first used as the receiving coil for IPT and also performs as the compensated inductance for CPT. By connecting one of its feed lines to the metal cover, only a parallel external capacitor is needed to construct the receiver of the proposed coupler because the metal cover and NFC antenna are components that already exist inside the smartphone, which greatly saves space inside the smartphone and cost for the proposed coupler. Prototypes of the proposed NFC-connected coupler with and without actual smartphone have been built. The wireless power transfer through metal cover by IPT and CPT has been validated via experiment.