Integrated fiber supercapacitor coils enabling wireless charging and passive voltage monitoring

Abstract

Fiber supercapacitors (FSCs) have attracted extensive research interest in the field of flexible electronics and wearable devices. This paper presents integrated FSC coils capable of inducing charging current between two electrodes in an alternating magnetic field, where FSC serves both as energy storage part and as an inductive coil, and rectifier diodes regulate charging current direction and maintain direct current bias of FSC. Using FSC as inductive coils leads to a concurrent increase in both energy storage capacity and energy harvesting ability as the device scale expands. This enables the aggregation of the total charging power when multiple coils are used for charging simultaneously. The charging principles reveal that the charging current is only induced and circulated inside the coil, ensuring each individual coil maintains its independence during multi-module charging and preventing the risk caused by the accumulation of large currents. The charging power of the device can be quantitively reflected by the pulse height (ΔUpulse) between two electrodes and voltage drop (Udrop) in one electrode, and analyzing these parameters enables rapid assessment of device performance. The integrated FSC coils also show compatibility with commercial wireless charging pads, expanding potential applications. In addition, the devices naturally function as LC oscillators, with resonant frequency tunable through the coil structure design. Replacing diodes with varactor diodes allows direct conversion of charging voltage into resonance frequency, permitting wireless readout. Such capability facilitates rapid identification and passive voltage monitoring across individual components during multi-module charging, presenting a viable approach for maintaining and managing large-scale, multi-coil systems.