Karalis, Kurs, Joannopoulos, and Soljačić reply: The results presented in our theoretical work 1 are relatively simple examples of how to implement our proposed scheme for wireless energy transfer. In practice, the system could be designed to operate at frequencies outside the ham radio band, to perform much better than Peter Anderson states (see, for example, section 4 of reference 1) by improving on the materials and geometries used, and to radiate below general safety and interference limits—for example, the IEEE (Institute of Electrical and Electronics Engineers, Inc) standards for general public exposure. 2 Safety and interference issues are very important and will have to be thoroughly investigated before any product development.
The physics of electromagnetic resonance and its use for transferring energy wirelessly has long been known and used to provide relatively low levels of power to various applications, as Herzel Laor states. Existing resonant-electromagnetic-induction technology has been inadequate to efficiently power, over mid-range distances, devices that require on the order of tens of watts of power or more. Our work demonstrates that it is the physics of strong coupling, for which resonance is a prerequisite, that enables the efficient wireless energy transfer needed for larger power applications. 1 The principles of this physical concept will certainly lead to improved engineering in designing actual systems.
In addition, strong coupling implies that the scheme is not radiative but rather uses the near stationary field; therefore, “hundreds of watts of RF” are not being radiated by our method, as numerical examples in reference 1 demonstrate.
