An Improved Rectenna Design for Battery-free Wireless Sensors and Structural Health Monitoring

This paper addresses the design and the characterization of an improved rectenna operating with low power density. As compact as possible, the surface of the fabricated rectenna is only 66 cm2 that is only 0.057 of a square wavelength at the operating frequency (868 MHz). A small size (15 $\mathrm{x}9\mathrm{cm}^{2})$ reflector plane behind the rectenna increases the amount of the harvested dc power of the rectenna: the harvested dc power is greater than 100 μW (dc voltage greater than 1V) when the rectenna is illuminated with radiofrequency power densities greater than $0.78\ \mu \mathrm{W}/\mathrm{cm}^{2}$. Additionally, a comparison between different configurations of the rectenna is presented.