## 1 Introduction  
Wireless charging is a beneficial technology, removing the usage of cables and connectors, which finds its place in many practical application areas such as consumer electronics, medicine, healthcare, automotive, industrial, communications, aerospace, and defense industries. The wireless charging market is valued in the range of USD multi-billions and is expected to experience massive growth in this decade [1]. The growth is determined by the boost of the battery-powered devices market [1, 2] and the development of methods and materials assuring high efficiency and affordability of the technology [3, 4]. After starting from relatively low-power application areas such as consumer electronics, medicine, communications, and sensing, wireless charging also has spread towards high-power applications [5, 6, 7]. A huge potential for high-power wireless charging technology is found in automotive applications, especially for electric vehicle battery charging. As climate change demands that we switch to environmentally friendly technologies, vehicle manufacturers shift their focus from conventional internal-combustion-engine-powered vehicles towards electric ones [8]. The rapidly growing number of electrical vehicles demands widespread and handily applicable EV charging infrastructure development, correspondingly [9]. In addition to the primary purpose of EV batteries, to store energy for their operation, together with acting as financially motivating tools, they are considered to be an additional tool helpful for the power balancing of electrical power systems [10; 11; 12]. Along with conventional conductive AC charging or DC off-board charging [13], wireless power charging appears to be an additional desirable option [14]. The nature of wireless chargers, allowing easy and safe [15; 16] connection and disconnection from the power network, is compatible with the users' demands. Consequentially, the topic of wireless power transfer among researchers has recently been experiencing a renaissance. One of the critical parameters determining the efficiency and power transfer capability of a WPT system is the coupling coefficient of the coupling coils [17]. In EV charging applications, the system must be capable of transferring high power with high efficiency through relatively large air-gaps [18]. Therefore, the analysis of the coupling coefficient of the coils' systems is receiving researchers' attention. A recently published wireless transferred power measurement method's error exhibited a dependence on the coupling coefficient, confirming its maximization benefits for accurate metering [19]. An optimization of the design is presented with respect to the coupling coefficient maximization of coil systems for EV charging applications by applying the finite element method in [20]. The focus of this work is set on research on ferrite saturation and its thickness optimization. A comparison of self and mutual inductances, as well as coupling factors of coils with circular and square geometries based on FEM analysis, is presented in [21]. The work presents an analysis of coreless structures, and core-based structures with and without aluminum shielding. However, different shape coupling systems with different numbers of ferrite bars and just the coil systems with symmetrical designs are compared in [21]. A method for magnetic structures for roadway WPT (Wireless Power Transfer) systems is proposed in [22]. The method is based on the simplified 2D finite element analysis of the coil systems. In [17], the influence of coil misalignment on coupling coefficient, mutual inductance, and quality factor, as well as the influence of the geometry of ferromagnetic backings on coupling coefficient, was investigated for the system of coils consisting of two identical circular coils. In [23], authors presented an analysis of the impact of coil misalignment on the coupling factor of coreless circular, square, rectangular, and DD coil systems.