How does wireless charging work?

How does wireless charging work?
Mains voltage is converted into high frequency alternating current (AC).
The alternating current (AC) is sent to the transmitter coil by the transmitter circuit.  The alternating current then induces a time varying magnetic field in the transmitter coil.
Alternating current flowing within the transmitter coil induces a magnetic field which extends to the receiver coil (when within a specified distance).

The magnetic field generates current within the receiver coil of the device.  The process whereby energy is transmitted between the transmitter and receiver coil is also referred to as magnetic or resonant coupling and is achieved by both coils resonating at the same frequency.
Current flowing within the receiver coil is converted into direct current (DC) by the receiver circuit, which can then be used to charge the battery.
Through the process described above, power can be transferred safely over an air gap and also through any non-metal object which might exist between the coils i.e. wood, plastic, granite.  The addition of extra (or larger) transmitter coils can also extend the range at which the power can be transferred.