Wearable Rectenna With Integrated Miniaturized Feeding Slot and Rectifier Structure

A low-cost hybrid textile/PCB wearable rectenna is designed for smart on-body applications. It is an integration of a textile patch antenna and a highly efficient rectifier on a small PCB substrate, where the feeding aperture of the antenna is significantly miniaturized by exploiting an LC loading technique to have an effective integration with the rectifier. The feeding-rectifying circuitry is attached to the back of the antenna by normal sewing threads. The essential components are soldered on the small rigid PCB for a robust connection. The size of the rectenna is $0.817\times 0.817\,\,\lambda {0}^{2}$ while the rigid substrate area for the feeding-rectifying circuitry is only $0.278\times 0.147\,\,\lambda {0}^{2}$ ( $3.4\times1.8$ cm) at 2.45 GHz. The intrinsic dielectric/conduction loss of textile feedlines, the loss of antenna-to-rectifier interconnectors, the loss of soldering or gluing on textiles, and the loss due to body absorption from typical large feeding slots are constitutively reduced. The soldering points and the consequent hard-to-be-characterized parasitic effects on textiles are avoided. The proposed integration approach reduces the cost and eases the rectenna design, fabrication, and integration. As a result, the power conversion efficiency (PCE) of the rectifier reaches up to 39.5% at -20 dBm input power level whilst the experimental rectenna prototype achieves the state-of-the-art PCE of 41% at an extremely low incident power density of $0.4~\mu \text{W}$ /cm2. The maximum PCE is 56% at the -5 dBm input power. Finally, the possibility of harvesting datalink energy from PC/mobile phones as power source for wearable electronics is investigated.