Hello, I have read a lot of literature in this area and am really confused. I need help. There is a drive today towards increasing the distance over which energy transfer is feasible. Currently, mutual induction is used commercially for a whole bunch of applications, but each of them requires that the air gap between the primary and secondary coils be small. Enter resonance induction: a special kind of induction that uses resonance; I have read that this phenomenon allows for the distance to be increased to a few times the size of the coils. The phenomenon that facilitates the transfer of energy is highly theoretical - "evanescent wave coupling." Literature compares this physics to http://en.wikipedia.org/wiki/Total_internal_reflection#Frustrated_total_internal_reflection" that occurs in wave-media interactions. In energy transfer applications, this evanescent field is seen in the "near field" region of a resonator (e.g., LC coil) My question is: what is the theoretical basis that supports the existence of such a wave in the vicinity of a resonator? and why does coupling of the evanescent wave allow for the air gap distance to be increased?