Physical Pictures and Performance Analysis of Wireless Power Transfer via Evanescent Fields

We present herein for the first time the physical pictures of wireless power transfer via evanescent fields. Our results show that the evanescent fields store energy in a localized domain and can exchange energy between two modes through evanescent waves. We also show that the energy transfer efficiencies can be greatly improved when long-tailed slowly-evanescent fields are adopted. We investigated the energy transfer efficiency and performance of wireless power transfer systems in detail and established their relationship with respect to the coupling strength and the output load parameters. Our theoretical analysis and computer simulations show that the work, radiation and absorption efficiencies are monotone functions of the coupling strength for a given output load parameter and there exists a global optimal output load configuration and a global optimal transfer rate for a fixed coupling strength parameter. The effectiveness, robustness and safety of this class of systems are also verified via the derivation of asymptotic behaviors of the optimum solutions.