**4. System overview**

There are many different types of WPT such as electromagnetic, electrostatic, electromechanical, etc. In the case of electromagnetic wireless power transfer, the systems are generally broken down into two categories of far-field and near-field power transfer [4].

In such systems, the energy transfer is accomplished through electromagnetic radiation, which for omnidirectional propagation scenario results in poor efficiency. The range that is the far-field region of a transmitter depends on the frequency of operation.

The idea behind WPT is simple. According to the Faraday's law of induction when a varying magnetic field passes through a loop it will produce a potential difference across it. In other words, a loop can harvest an alternating magnetic field which then can be converted and stored as electrostatic energy [5].

Generating, the required magnetic field can be done through Amperes law. Amperes law states that when an electric current flow through a loop, let us call it the transmitter loop, it generates a magnetic field around it.

Now, if we place a second loop, let us call it the receiver loop, in the proximity of the transmitter, an alternating voltage will appear across the receiver loop. Hence effectively transmitting power through electromagnetic waves.
