1. Transformer coupling
Energy transfer between two coil through magnetic fields
but in this method, distance between two coils should be too close.
2. Resonant induction coupling (Evenescent wave coupling)
Electro magnetic wave in a high angular waveguide is called as evenescent waves which carry no energy, when if a proper resonant waveguide is brought near the transmitter then a tunnel is formed to the power drawing waveguide which can be converted in DC using rectifier circuits.
A prototype model is achieved with 5 meters of ranges with this method.
3. Radio and microwave energy transfer:
with this method a long range is possible. In this method microwave is sent to the long distances and can be received through rectenna which extract microwave energy back to electrical energy. But the problem with this methods is that the diameter of antenna should be order of km.
4. Laser beam transfer
In this method, laser is beamed to the photo voltaic cells which extracts the electrical energy
5. Electrical conduction method
In this method, while tranfer energy through wires or conductors, when the voltage reaches the breakdown voltage, the sorrounding medium start conducts, in this way the enegy can be transfered through air medium.
Though there are several methods available, in practical cases there is no device for transmitting power wirelessly with high energy capacity. But at low power transfer there are so many devices available in the market.