Synergistic multi-source ambient RF and thermal energy harvester for green IoT applications

Abstract

In a future green Internet of Things (IoT) reality, billions of devices of the IoT infrastructure should be self-powered. Harvesting ambient energy to power IoT devices is an attractive solution that can extend battery life or can completely replace batteries. Considering the global applications of IoT, ubiquitous and continuous availability is an important requirement for ambient energy sources. Radio frequency (RF) energy from mobile phone towers and thermal energy from diurnal cycle temperature fluctuations are good candidates. In this study, we present a synergistic multi-source energy harvester (MSEH) comprising an RF energy harvester (RFEH) and a thermal energy harvester (TEH) integrated through a dual-function component, heatsink antenna. Both harvesters collect ambient energy 24 h a day and are not location specific. The TEH, which is in the shape of a box, collects energy using heatsinks on its sidewalls. The same heatsinks are optimized to also serve as receiving antennas of the RFEH, which collects energy from the GSM900, GSM1800, and 3G bands. Due to the synergistic integration, radiation efficiency of the antenna doubled from 40% to 80% which resulted in ∼10% increase in power conversion efficiency of the RFEH. Similarly, the average power of the TEH without heatsinks 120 μW is doubled to 240 μW for TEH with heatsinks. Field tests have shown that the outputs of the TEH and RFEH have increased 4 and 3 times compared to the independent TEH and RFEH respectively. A temperature and humidity sensor based IoT node has been successfully powered through this energy harvesting system. Overall, the MSEH can collect 3680 μWh of energy per day which is sufficient to obtain the sensors data with a time interval of 3.5 s.