Dual-Receiver Wearable 6.78 MHz Resonant Inductive Wireless Power Transfer Glove Using Embroidered Textile Coils

Abstract

The design of dynamic wearable wireless power transfer systems (WPT) possesses multiple challenges that affect the WPT efficiency. The varying operation conditions, such as the coils' coupling, and operation in proximity or through the human body, can affect the impedance matching at the resonant frequency. This paper presents a high-efficiency wearable 6.78 MHz WPT system for smart cycling applications. Resonant inductive coupling using dual-receiver textile coils is proposed for separation-independent WPT, demonstrated in a smart cycling glove, for transferring energy from an on-bicycle generator to smart-textile sensors. The effects of over-coupling in a dynamic WPT system have been investigated analytically and experimentally. The embroidered coils efficiency is studied in space, on- and through-body. The measured results, in space, show around 90% agreement between the analytical and experimental results. To overcome frequency-splitting in the over-coupling region, an asymmetric dual-receiver architecture is proposed. Empirical tuning of the lumped capacitors is utilized to achieve resonance at 6.78 MHz between the fundamental frequency and the even mode split frequency. Two different coil sizes are utilized to achieve separation-independent efficiency in the tight coupling region on- and off-body, while maintaining a Specific Absorption Rate (SAR) under 0.103 W/kg. The presented system achieves a peak efficiency of 90% and 82% in free space and on-hand respectively, with a minimum efficiency of 50% under loose and tight coupling, demonstrating more than 40% efficiency improvement over a 1:1 symmetric transmit and receive coil at the same separation.