Broadband Radio Frequency Energy Harvesting

Abstract

In this project, a broadband energy harvesting rectenna is presented over the frequency band of 3G, 4G, and Wifi. This frequency band, from 1.8 to 2.5 MHz, is determined after the consideration of the overall ambient power available in the environment and the rectenna is optimized for the corresponding input power level. For harvesting radio frequency energy, broadband designs can accumulate more energy from the environment and produce a higher DC output power, even though they have lower overall efficiency and a larger dimension than narrowband design, which this project also aims to overcome. Since the functionality of rectenna depends heavily on the rectifying circuit, matching circuit and the antenna portion. First, a Greinacher voltage doubler is used to enhance its sensitivity, efficiency, and performance in a low power density environment. Then, a two-branch impedance matching circuit is used to widen its bandwidth with a compact circuit design. After that, a broadband dual-polarized cross-dipole antenna is used to improve its adaptability to the environment within the targeted bandwidth. The measured sensitivity of the rectenna is lower than -10dBm and the overall conversion efficiency reaches 8.2% when the power input to the rectifying circuit is -10dBm. Moreover, the highest recorded open circuit voltage output reaches 0.85V in the practical outdoor environment. Therefore, this proposed energy harvester is capable of power many low-power electronic devices which will be abundant in the coming IoT trend.