Wireless Charging Coils TDK Wireless Charging Coils for smart phones and other mobile devices employ a proprietary flexible thin metal magnetic sheet, achieving an industry-leading thickness of only 0.52mm. These TDK wireless power transfer coil units are ultra-thin, lightweight and highly resistant to shock. The design of the coils minimizes the tendency toward rising resistance and achieves a power transfer efficiency that meets the requirements of the WPC Qi standard. These TDK devices also have a low height and an output current of 0.5 to 0.6A.