Wireless charging with textiles through harvesting and storing energy from body movement

This paper presents a wireless charging method based on textiles through harvesting and storing energy from human movement. The proposed method uses resonant coils made of a conductive yarn and a flexible printed circuit board. The conductive yarn consists of polyurethane-coated copper and polyester filaments. The transmission characteristics of the resonant coils, which were worn on the arm of a human body, were evaluated using simulation and measurement tools. It was determined that the change in the resonant frequency of the conductive-yarn resonant coils can be obtained from the coil length, stitch intervals, and fabric thickness using equations. The measured resonant frequencies of the sending and receiving coils were designed to achieve a resonant frequency of 13.56 MHz when the coils are worn. The resonant coils were worn on the arm of a subject, who moved at various speeds, and the transmission efficiency was measured using an alternating current–direct current converter. The measurement results showed a maximum transmission efficiency of 55.1%, even though the resonant coils were worn around the arm and not the leg, and an average transmission efficiency of 52.1% when the subject was moving at a speed of 6 km/h.