*Wireless Power Transfer DOI: http://dx.doi.org/10.5772/intechopen.99990*

**Figure 2.**

In addition to the near-field, it can be further subdivided into the reactive (nonradiative) near-field and the radiative. The wavelength of the field source is normally used to define these limits as shown in **Figure 2**. As a consequence, an electromagnetic (EM) wave's wavelength, which is proportional to its energy, defines how it interacts with its surroundings. Its limits depends on the wavelength *λ* [5]. The boundary of the Radiative region is about 1 wavelength, and up to 2*λ* where a transition region take place. Over than 2*λ* distance from the transmitter, the far field area starts.

The reactive (non-radiative) region is on the very short range of *λ=*2*π* and it is based on the capacitive or the mutual inductance effect of the antenna. The are used two term to indicate the distance of the transmission: short-range and mid-range. The short-range refers to a transmission wavelength that is less than the transmitter's geometry. The mid-range describes a condition in which the transmission gap is at least two to three times the size of the equipment involved in the power transfer [6].
