AC Resistance Reduction of a Flexible Wireless Power Transmission Coil Using Magnetic Path Control Technology at 13.56 MHz

To reduce the size and weight of wireless power transfer devices, lightweight, thin, and highly efficient power-transmitting and power-receiving coils are required. In this paper, we describe a spiral-shaped flexible flat wire coil with reduced ac resistance, which is suitable for being mounted on electric tools and smart phones. A method for reducing the ac resistance of a flexible coil for wireless power transfer at high frequencies is required. The proposed flexible coil uses magnetic path control technology to suppress the skin and proximity effects by applying a magnetic material to the coils. The proposed coil reduces the ac resistance by 18% at 13.56 MHz in the ISM band, and improves the Q value of the coil by 27%. As a result, the transmission efficiency improves by 1.3% when the distance between the coils in 10 mm.