Wireless Electricity: Magnetic Resonance vs. Magnetic Induction

[beonfilms]

What is the difference between magnetic resonance and magnetic induction when it comes to charging devices and other types of wireless electricity. I was doing some research on this but was not able to find a clear answer. If someone could help me with this that would be greatly appreciated.

With kind regards,
Ben

 

[Drakkith]

Per wiki: http://en.wikipedia.org/wiki/Resonant_inductive_coupling

Resonant transfer works by making a coil ring with an oscillating current. This generates an oscillating magnetic field. Because the coil is highly resonant, any energy placed in the coil dies away relatively slowly over very many cycles; but if a second coil is brought near it, the coil can pick up most of the energy before it is lost, even if it is some distance away. The fields used are predominately non-radiative, near field (sometimes called evanescent waves), as all hardware is kept well within the 1/4 wavelength distance they radiate little energy from the transmitter to infinity.

Non-resonant coupled inductors, such as typical transformers, work on the principle of a primary coil generating a magnetic field and a secondary coil subtending as much as possible of that field so that the power passing though the secondary is as close as possible to that of the primary. This requirement that the field be covered by the secondary results in very short range and usually requires a magnetic core. Over greater distances the non-resonant induction method is highly inefficient and wastes the vast majority of the energy in resistive losses of the primary coil.

The use of resonant inductors allows the two coils (in this case the charging device and the object being charged) to be placed much further apart than non-resonant coupled inductors, which are typically right next to each other or one is inside the other. Note that induction is occurring in both cases. In a non-resonant coil an oscillating current won't be sustained. It will simply die off as soon as you stop applying the power. Current in a resonant coil will continue to oscillate back and forth until resistive and radiative losses use up all the energy.