MI wireless charging works via Inductive Coupling.
In the most basic form, a circular magnetic field is formed around the wire when an electrical current is passes through. When the wires are bent into coils, the magnetic fields are amplified - as the loops of the coil increases, so those the magnetic field. Placing a second coil of wire in the magnetic field created would induce a current into the wire. (This is similar to how a transformer works)
i.e. The transfer of electricity from L1 to L2 can be seen in FIgure 1.1.
This is essentially how contact based chargers work, where wireless charging works over short distances. Inductive Coupling is commonly seen in electric toothbrushes and wireless charging mats.
RB wireless charging works via resonant based indicutive coupling. Harnessing the technology utilised in Inductive coupling and the physics principles of resonance frequency.
The distance at which the energy can be transferred is increased if the transmitter and receiver coils are resonating at the same frequency.
As objects have a certain frequency by which they start vibrating, a receiver and a device in tune can communicate with each other over the same frequency. This technology allows electricity to transfer over distances of up to four feet - with large possibilities for aplication.
Radio Frequency
All wireless devices, including cell phones, Bluetooth, Wi-Fi and wireless charging, use radio frequencies (RF), though the operating frequency differs depending on the use. The radio frequency spectrum is grouped into bands ranging from 3 kHz (kilohertz) to 300 GHz (gigahertz). RF is the electromagnetic field (EMF) spectrum, comprised of electric and magnetic fields present everywhere in our daily environment. EMF spectrum comes from both natural and man-made sources.
Wireless charging technologies operate at a specific frequency or frequency-range on the radio spectrum.
Magnetic Induction (MI)
FIgure 1.1. - Depiction of Induction based charging
Resonant Based (RB)
Radio Frequency (RF)
Detailed Research at : http://d-scholarship.pitt.edu/8474/1/Harrist_Thesis_072804.pdf
