Examination and analysis of efficiency for air gap and characteristic impedance in wireless energy transfer

Wireless energy transfer has become one of the attractive research topics in recent years and is now one of the fields in which many researchers state their different approaches. The very first energy transfer studies was started by Nicola Tesla and the present day studies make it possible to have applications which are hard to be supplied by cables but by wireless energy as the preferred method. The main target for wireless energy transfer is to store the energy within a coil in the magnetic resonance circuit and then to transfer this stored energy to another coil in the very same circuit. In order to have the energy transferred from the primary coil to the secondary coil effectively, two conditions have to be fulfilled. The first condition is to have a very compact coil size and utilize high frequency for better energy transmission. The second condition on the other hand is to have good magnetic coupling between the two coils. The effect of magnetic resonance circuit on the wireless energy transfer system is not only affected by the parameters of the system itself but by the distance between the two coils. Therefore in this study, depending on the air gap values as well as the applied frequency, the behavior of the system under various load conditions has been analyzed such that depending on the change of voltage and power for these two parameters and the system efficiency is observed. In order to calculate parameters like current and voltage as a function of frequency at various air gap values and load conditions, analysis depending on different parameters were made by running system simulations on three different simulation platforms and the efficiency values of each system gathered from these simulations have been compared. It was observed that the distance between the coils responsible for energy transfer should be kept at an optimum value since any increase of the air gap value will degrade the energy transfer ratio. This problem could be solved by optimizing the relation between frequency and quality factor. Keywords: Wireless energy transfer, magnetic coupling, magnetic resonance circuit, characterictic impedance