E-Textile RF Energy Harvesting and Storage using Organic-Electrolyte Carbon-Based Supercapacitors

Wearable radio frequency (RF) energy harvesting is highly dependent on the distance from the source and human-caused RF shadowing. Therefore, energy storage devices integrated with rectennas are of paramount importance to overcome this intermittency. In this paper, the use of carbon-based e-textile supercapacitors for storing the RF-DC converted power for powering body area networks nodes is investigated. A voltage doubler sub-1 GHz flexible rectifier, whose peak power conversion efficiency (PCE) approaches 80% is coupled to a two-cell 15.5 mF textile-based supercapacitor operating up to 4 V DC. Owing to the rectifier's low optimum load resistance and high DC Voltage output, the average charging PCE of the rectifier-supercapacitor module reaches 31% for a 9.5 dBm input. Time-varying s-parameter measurements are performed to compare the time-averaged matching as opposed to instantaneous measurements using a resistive load, where the textile supercapacitor exhibits a similar response to a commercial supercapacitor. Finally, the RF-charged textile supercapacitor is demonstrated, for the first time, powering a microcontroller and Bluetooth transmitter with an average power consumption of
$350\ \mu \mathrm{W}$
for up to 102 s, following 40 s of charging at 9.5 dBm, demonstrating its suitability for RF-powered body area networks applications.