Coils Fabricated with Sewing Litz wire and Application to Wireless Power Transmission

Abstract

　Flexible and high-conductive coils are required to deliver power wirelessly to wearable devices. This paper describes coils fabricated with sewing high-conductive Litz wire and wireless power transmission using the coils. Those coils are fabricated by using some sewing techniques such as hand sewing, sewing machine and a punch needle method. A coil with 15 turns and a 150 mm × 150 mm square shape has 60 - 120 of the Q-factor at measurement frequencies from 100 kHz to 1000 kHz. A wireless power transfer system was built with the coil. A power oscillator was used in the system in order to adjust the operating frequency automatically. Maximum AC power efficiencies were around 0.44 - 0.99 at the coil distances from 0 to 150 mm in the prototype system. Durability against washing and effects on deformation were discussed.