Investigation of Near-Field Wireless Power Transfer Under Multiple Transmitters

We derive the upper bound for wireless power transfer in the near-field region under the multiple-transmitter scenario. It is found that a stable region in power transfer efficiency (PTE) can be created for sufficiently close spacing between two transmitters, in contrast to the monotonic decay of the single-transmitter case. We next demonstrate through simulation and measurement that such a bound can be approached by using efficient, electrically small, folded cylindrical helix dipoles. The measurement shows a 17% PTE value over a 0.3λ region between the two transmitters, corroborating the theory and simulation. Results from the four-transmitter case show that the stable PTE region can be extended to two-dimensional space.