**4.2 Coupling elements design**

The most important parameter in the design of coupling coils is undoubtedly the product of quality factors *Q* and coupling *k*. Its operating size is strongly dependent on various parameters (e.g. circuit topology, load size, coil distance, etc.) and therefore cannot be optimized directly. One option is to maximize the quality factor. To achieve maximum inductance, we make the coil as planar with square turns (**Figure 23**). In addition, due to the limitation of parasitic capacitance (we now neglect), we keep constant spacings between individual turns of size *δ<sup>v</sup>* = 4 mm. Geometric dimensions allow to wind about 26 turns. In addition, if we know the

*Theoretical and Practical Design Approach of Wireless Power Systems DOI: http://dx.doi.org/10.5772/intechopen.95749*

operating frequency, we can determine the voltage drop and the current through the coil from the required power. It is necessary to design an effective winding cross section for this.

Regarding the available conductor cross-sections, a copper wire (2200 mutually insulated conductors) with a total cross-section of *Sv* = 19.63 mm2 was selected. The winding produced in this way eliminates the effect of the skin effect and the resulting resistance of the coil is therefore only affected by the phenomenon of proximity.

The coil has 22 turns, the calculation parameters being as follows. The selfinductance has a value *L* = 147 μH and the active resistance is *R* = 0.19 Ω.
