Indoor WiFi energy harvester with multiple antenna for low-power wireless applications

This research proposed a WiFi energy harvester for low-power wireless applications. The proposed system harvests energy using three antennas to cover three ISM (Industrial, Scientific, and Medical) channels with central frequencies at 2.412 GHz, 2.439 GHz, and 2.462 GHz. For each channel, a co-planar waveguide antenna is designed to harvest energy from indoor WiFi transmitters. FR4 substrate with relative permittivity of 4.3 and loss tangent of 0.025 is used to form the antennas. The output from each harvester antenna is then connected to a seven-stage multiplier circuit. The multiplier circuit is to rectify and boost the harvested energy to a higher voltage level and then stored temporarily in a super capacitor. A dc-dc boost-charger circuit with battery management is used to increase the output voltage level to 2 V. An experiment with the proposed system has been conducted using transmitted energy from available WiFi transmitters. The power density at the harvesting antenna front is between -80 dBm and -50 dBm. The proposed harvester system takes about 6 to 7 hours to charge up the first stage super capacitor up to the minimal threshold voltage (0.45V). This minimal threshold will start the boost-charger circuit charging the secondary storage device. This research demonstrates that the proposed system can supply energy for low-power wireless sensors that operate with an input power less than 1 mW.