Coherently enhanced wireless power transfer: theory and experiment

Extraction of electromagnetic energy by an antenna to a coupled waveguide is the crucial part of wireless power transfer. Efficiency of this process is usually defined by the coupling strength between the antenna and the outcoupling waveguide or cable. We show that there is an additional possibility to improve the receiving efficiency by coherent excitation of the outcoupling waveguide by a backward propagating guided mode with a specific amplitude and phase. This additional wave creates a special interference picture in the system and result in increased amount of energy extracted to the waveguide from the free space. We develop a simple analytical model predicting this effect, demonstrate it in numerical FDTD simulations, and verify in microwave experiment. (paper)