Evanescent wave coupling
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Evanescent wave coupling is a process by which electromagnetic waves are transmitted from one medium to another by means of the evanescent (or decaying) electromagnetic field(s). This is usually accomplished by placing two or more waveguides close together so that the evanescent field does not decay much in the vicinity of the other waveguide. Assuming the receiving waveguide can support mode(s) of the appropriate frequency, the evanescent field gives rise to propagating wave mode(s), thereby connecting (or coupling) the wave from one waveguide to the next.
Evanescent coupling is always associated with matter, i.e. with the induced currents and charges within a partially reflecting surface. This coupling is directly analogous to the nearfield, non-radiative coupling between the primary and secondary coils of a transformer, or between the two plates of a capacitor. Mathematically, the process is the same as that of quantum tunneling, except with electromagnetic waves instead of quantum-mechanical wavefunctions.
[edit] Applications
Evanescent wave coupling is used to excite dielectric microsphere resonators among other things. A new application could be wireless energy transfer, useful, for instance, for charging electronic gadgets without wires.
[edit] References
- Karalis, Aristeidis; J.D. Joannopoulos, Marin Soljačić (November 2006). "Efficient wireless non-radiative mid-range energy transfer". arXiv:physics/0611063. Retrieved on 2007-02-24.
- "'Evanescent coupling' could power gadgets wirelessly", Celeste Biever, NewScientist.com, 15 November 2006
- Wireless energy could power consumer, industrial electronics - MIT press release
