The power transferred increases with frequency[REF] and the mutual inductance M between the coils,[REF] which depends on their geometry and the distance Drange between them.
Resonant inductive coupling (electrodynamic coupling,[REF] strongly coupled magnetic resonance[REF]) is a form of inductive coupling in which power is transferred by magnetic fields (B, green) between two resonant circuits (tuned circuits), one in the transmitter and one in the receiver (see diagram, right) [REF].