RF-Powered Wearable Energy Harvesting and Storage Module Based on E-Textile Coplanar Waveguide Rectenna and Supercapacitor

This paper presents a high-efficiency compact (
$0.016\lambda _{0}^{2}$
) textile-integrated energy harvesting and storage module for RF power transfer. A flexible 50
$\mu \text{m}$
-thick coplanar waveguide rectenna filament is integrated with a spray-coated supercapacitor to realize an “e-textile” energy supply module. The meandered antenna maintains an
$S_{11}< -6$
dB inside and outside the fabric and in human proximity with a 2.3 dBi gain. The rectifier achieves a peak RF-DC efficiency of 80%, across a 4.5
$\text{k}\Omega $
load, and a 1.8 V open-circuit voltage from −7 dBm. The supercapacitor is directly spray-coated on a cotton substrate using carbon and an aqueous electrolyte. When connected to the supercapacitor, the rectifier achieves over an octave half-power bandwidth. The textile-integrated rectenna is demonstrated charging the supercapacitor to 1.5 V (8.4 mJ) in 4 minutes, at 4.2 m from a license-free source, demonstrating a significant improvement over previous rectennas while eliminating power management circuitry. The integrated module has an end-to-end efficiency of 38% at 1.8 m from the transmitter. On-body, the rectenna’s efficiency is 4.8%, inclusive of in-body losses and transient shadowing, harvesting 4 mJ in 32 seconds from 16.6
$\mu \text{W}$
/cm
²
. It is concluded that e-textile rectennas are the most efficient method for powering wearables from
$\mu \text{W}$
/cm
²
power densities.