An NFC-CPT-Combined Coupler With Series- None Compensation for Metal-Cover Smartphone Applications

A near-field communication capacitive power transfer (NFC-CPT)-combined coupler with a series-none compensation topology is proposed for metal-cover smartphone applications. To achieve capacitive power transfer through metal cover, the metal cover itself is used as the receiving metal plates. To realize NFC through metal cover, the cross slot including a slim horizontal slot and a rectangular slot is embedded on the metal cover, which mitigates the eddy current loss and increases the inductive coupling for the NFC antenna. Besides, the cross slot divides the metal cover into two separate metal plates, which is necessary for capacitive power transfer. Considering the space limitation and safety requirement, no compensation components are integrated inside the smartphone and only a series inductance is integrated on the transmitter side. A prototype of the proposed NFC-CPT-combined coupler has been built. The wireless power transfer and NFC through metal cover have been validated through experiment. The experimental results show that the prototype achieves 5-W output power with a 93.5% circuit efficiency at 6.78 MHz, and the detection range of the NFC antenna is 61 mm.