Radiofrequency energy harvesting system based on a rectenna array in urban environments

Energy harvesting has become very attractive due to the extended usage time of devices. Among several forms of recycling energy, radiofrequency (RF) harvesting has been suggested due to its wide availability mainly in urban areas. Its applications range from sensor nodes to charging low power consumption portable devices and depend on the amount of antennas. In this paper, we evaluate the feasible application of RF harvesting for charging a cell phone. To validate our analysis, we conduct an RF measurement campaign at four important locations in Brasilia, Brazil. Considering the average incidence of 11 dBm, we achieve the final value of 2.5 mW/m2. With an incident power of +10 dBm, only 2 rectennas per hour are needed to charge a cell phone whose battery is approximately 3.72 mWh. We perform a comparison between rectenna arrays and simple antennas directly connected to one external matching circuit, dismissing adaptive beamforming circuits as a way of avoiding intermediate energy losses. In order to apply RF energy harvesting in higher power consumption devices, we propose a rectenna array system which increases considerably the amount of recycled power. For both Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) paths, harvesting systems based on rectenna arrays outperform standard antenna array based solutions.