Large air gap misalignment tolerable multi-coil inductive power transfer for wireless sensors

The efficiency of wireless power transmission via electromagnetic induction is strongly dependent on the distance and the lateral misalignment between the sending and the receiving coils. In this study, the authors propose to adopt a multiple-input-single-output (MISO) coil system to increase the efficiency of energy transmission in case of large air gap misalignment between coils. The sending part consists of a matrix of air-core coils, in which only the four coils under the receiving coil, supplied with the same current, contribute to energy transmission. To orientate the magnetic field and to reduce the energy losses, they propose to power the two nearest neighbour coils with low, out-of-phase, excitation current. A simplified analytic model of the multi-coil system configuration is developed, whereas the mutual inductance and the coupling factor are determined by numerical simulations. To validate the analytical and simulation results, an experimental setup was built. Both simulation and experimental results at a distance of 83% of the receiving coil diameter show that the proposed MISO coil system improves the received power and reaches at the same time a much better efficiency than that of two-coil systems.