Contents I. Introduction
Wireless Power Transfer (WPT) is assuming a role of primary importance in numerous sectors. This technique is already widely used for electric vehicle battery charging [1]–[3], underwater robotics [4] [5], biomedical plants [6] [7] and railway applications [8]–[10]. Thanks to the possibility of transferring power through an air gap, it avoids the use of bulky cables making the system simpler and lighter [11]–[12]. Two main group of WPT system can be identified: inductive (IWPT) and capacitive (CWPT) wireless power transfer systems. The IWPT exploit the magnetic induction between two coils, while CWPT systems exploit the electric field generated between two metal plates. While IWPT is already a mature technology and numerous devices are already available in the market, CPWT systems are still a relatively new technology. Since in a CWPT the power is transferred using cheap metallic plates and does not require high-cost magnetic cores and litz wires, it represents a cheaper solution with respect to IWPT [13]. In addition, since the power is transferred through an electric field between the metal plates, this technology is characterized by lower electromagnetic emissions with respect to IWPT systems where the magnetic field between coils tends to propagate in any direction [14].
