Wireless Electricity or WiTricity is rooted in such well-known laws of physics that it makes one wonder why no one thought of it before. In the past, there was no great demand for such a system, so people did not have a strong motivation to look into it.
WiTricity is based on using coupled resonant objects. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects. A child on a swing is a good example of this. A swing is a type of mechanical resonance, so only when the child pumps her legs at the natural frequency of the swing is she able to impart substantial energy.
In any system of coupled resonators there often exists a so-called "strongly coupled" regime of operation. If one ensures to operate in that regime in a given system, the energy transfer can be very efficient.
Various methods of transmitting power wirelessly have been known for centuries.Perhaps the best-known example is electromagnetic radiation, such as radio waves Since radiation spreads in all directions, a vast majority of power would end up being wasted into free space.