**2. The near-field transmission**

An electric power is transmitted from a source such as a generator or a battery to a load if an electric potential differential is applied over a conductor. The use of cables and wires to link the source to a load is the preferred method to allow the electrons flow. However, electronic devices are getting smaller and more compact as technology progresses. Obtaining energy from a cable attached to a power outlet can no longer be a viable option. Mobile devices that involve a smart power supply management are being built and implemented. As a result, a wired connections restrict their mobility and, in some situations, may not be a secure choice if they are damaged.

Electrical energy can be converted into other types of energy that can be transmitted through a particular medium without the use of conductive wires. The use of radio waves to transmit information, such as sound, video and data is a clear example of transmitting energy wirelessly. In a radio station, a voltage signal reflecting the information is produced and then converted into an electromagnetic energy pulse, which is broadcast into the atmosphere, where it spreads in all directions. An antenna detects the electromagnetic energy signal at a lower energy frequency. This signal is then converted back into an electrical voltage signal from which the information is derived.

Depending on the distance between transmitter and receiver, the power can also be converted in energy and then transmitted. Electromagnetic waves are generated in the surrounding media by any electromagnetic field source (point particle, dipole, antenna, or coil). The electromagnetic waves are distinguished by the properties of the fields and how these are associated with the medium in which they are travelling. These fields are normally divided into two types: the near-field and far-field (shown in **Figure 1**), based on their distance from the source and, more specifically, the characteristics of the dominant waves in this area.

**Figure 1.**

*Representation of wireless power transmission in (a) far field where is highlighted the rectenna, and (b) near field.*
