How exactly does WiTricity's wireless power transfer using resonance work? The WiTricity group has made a lot of buzz but no internet article explains the exact method that they are using. Does anyone know how it works?
 A: I don't really see anything new or unique about what they are doing.  They are just making a near-field resonator.  They avoid publishing their true efficiency numbers which is really the only characterization that matters.  There are some numbers of 42% efficiency on wikipedia.
Basically their 9.9 Mhz demos are just transformers with an air gap for coupling.  Their "resonance" claims are really just hype because no one would try to design a coupled system without making it resonant at the operating frequency.
Likewise simulating SAR is very different from the real SAR and they are using those simulations as part of their efficiency calculations which is suspect.  There are no actual studies or reports are claimed of the specific technology, power levels and use in home environments.
There's a paper on their dielectric resonators that you can read.
A: The method that WiTricity implements is that of magnetic resonance coupling.  Resonance is done to ensure efficient exchange of energy between the transmitter and the receiver.
The method is very simple. If you take a coil and pass alternating current through it, it will produce alternating magnetic field around itself (like a solenoid). Now, place another coil in the vicinity of the first coil. The alternating magnetic field causes alternating flux through the second coil. This generates an emf in second coil and hence provides power to load.
Witricity's method created a buzz because they portrayed it as a new invention but actually its just an improved version of inductive coupling.
A: This is only comment-worthy, but I don't have the reputation for a comment yet.
https://web.archive.org/web/20131207183005/http://witricity.com/pdfs/highly-resonant-power-transfer-kesler-witricity-2013.pdf
That paper from WiTricity has some more detailed descriptions and a bit of math.  It also cites references if you'd like to follow up on some details.  So hopefully it can satisfy your curiosity a bit deeper.
