RFID-Enabled Energy Harvesting using Unidirectional Electrically-Small Rectenna Arrays

RFID has been widely adopted in sensing applications based on passive tags. We present, for the first time, a practical room-scale demonstration of a wireless power grid based on 868 MHz UHF RFID, with 27 dBm radiated power. The proposed harvester is a state-of-the-art flexible rectenna surface based on serially-connected tightly-coupled electricallysmall rectenna elements. Reflector-backing is proposed increasing the harvester’s effective area by 3 dB with over two-fold increase in the harvested energy. The DC power harvesting pattern of the array are experimentally characterized showing an 18 dB front-to-back ratio. In a 40 m
²
room with a single reader and 3 antennas, a maximum energy of 5.3 mJ was harvested using the unidirectional array in a capacitor over a 1-minute charging period. The minimum energy yield of 0.5 mJ, sufficient for powering a Bluetooth beacon, evidences that, despite its intermittency, RFID packets can create an indoor RF grid.