Analysis of Multi-Coil Omnidirectional Energy Harvester

An omnidirectional energy harvester with a multi-coil structure for the wireless power transfer (WPT) system is proposed and analyzed. Compared with the traditional single-direction receivers, this harvester can provide more homogenous output power with relatively high transmission efficiency under arbitrary transmission directions. An analytical solution for mutual inductance calculation in the WPT system with multiple coils is derived. The influence of the mutual inductance under different angle inclinations on the magnetic flux leakage and transmission efficiency is analyzed accordingly. The proposed energy harvester has successfully transmitted over 20 W power with 110 mm, which is over twice of the radii of the receiving coils. The transmission directions can vary over 0°-360° with an efficiency of around 85% and the output power fluctuation within 5%. Thus, the performance is much better than the traditional receiver on both efficiency and stability of output power, especially when transmission direction changes or the receivers have a relatively large misalignment. The proposed energy harvester is particularly attractive for wireless charging of moving devices with 3-D trajectories such as drones or medical equipment.