Wireless Energy Harvesting for Internet-of-Things Devices Using Directional Antennas

With the rapid development of the Internet of Things, the number of wireless devices is increasing rapidly. Because of the limited battery capacity, these devices may suffer from the issue of power depletion. Radio frequency (RF) energy harvesting technology can wirelessly charge devices to prolong their lifespan. With the technology of beamforming, the beams generated by an antenna array can select the direction for wireless charging. Although a good charging-time schedule should be short, energy efficiency should also be considered. In this work, we propose two algorithms to optimize the time consumption for charging devices. We first present a greedy algorithm to minimize the total charging time. Then, a differential evolution (DE) algorithm is proposed to minimize the energy overflow and improve energy efficiency. The DE algorithm can also gradually increase fully charged devices. The experimental results show that both the proposed greedy and DE algorithms can find a schedule of a short charging time with the lowest energy overflow. The DE algorithm can further improve the performance of data transmission to promote the feasibility of potential wireless sensing and charging applications by reducing the number of fully charged devices at the same time.