Textile-based Radio Frequency Energy Harvesting and Storage using Ultra-Compact Rectennas with High Effective-to-Physical Area Ratio

Wearable Radio Frequency (RF) rectennas do not require expensive or hazardous materials and can be easily integrated with conventional e-textiles. In this paper, we investigate the use of ultra-miniaturized wire-type monopole antennas for energy harvesting (EH) applications, as a method maximizing the effective collection area of a rectenna relative to its physical size, while not reducing the net DC output. The rectenna, operating in the 915 MHz band, is integrated with a simple carbon-based e-textile supercapacitor for direct energy conversion and storage. The integrated module is then demonstrated, for the first time, wirelessly-charging a Bluetooth Low Energy sensor node at over 1 m distance from a license-free Powercast transmitter. The 14.1 mF supercapacitor is charged using the e-textile rectenna filament in 83 s up to 4.14 V, from an incident power density of 23.9 μW/cm2 and a time-averaged efficiency over 40%, enabling the sensor node to sustain operation for 108 s after the wireless RF source is stopped. Compared to state-of-the-art RF energy harvesters, the proposed module achieves over five fold improvement in the RF to DC power harvesting efficiency normalized to the harvester’s area.