Types of Wireless Power Transmission
Near Field :-
Near-field wireless power transfer operates based on the near-field electromagnetic coupling of coils or by electric fields using capacitive coupling between metal electrodes. Such a system can transmit power over a relatively short distance that is of the same order of magnitude as the coupled coils. The power transmission distance can be increased with flat relay resonators. Near-field behaviors dominate close to the antenna or scattering object.
Near-field E (electric) and B (magnetic) field strength decrease more rapidly with distance: the radiative field decreases by the inverse-distance squared, the reactive field by an inverse cubed law, resulting in a diminished power in the parts of the electric field by an inverse fourth-power and sixth-power, respectively. In the near-field region, radiation absorption affects the load on the transmitter. The magnetic induction seen in transformers can be seen as a very simple example of this type of near-field electromagnetic interaction.
Far Field :-
Far-field methods reach longer ranges, often many kilometers, where the distance is much larger than the diameter of the device.
High-directivity antennas or well-collimated laser light produce a beam of energy that can be made to match the shape of the receiving area. The maximum directivity for antennas is physically limited by diffraction.
