In wireless energy transfer systems, the energy is transferred from a power source to an electrical load without the need of physical\nconnections. In this scope, inductive links have been widely studied as a way of implementing these systems. Although high\nefficiency can be achieved when the system is operating in a static state, it can drastically decrease if changes in the relative position\nand in the coupling coefficient between the coils occur. In this paper, we analyze the coupling coefficient as a function of the distance\nbetween two planar and coaxial coils in wireless energy transfer systems. A simple equation is derived from Neumann�s equation\nfor mutual inductance, which is then used to calculate the coupling coefficient. The coupling coefficient is computed using CST\nMicrowave Studio and compared to calculation and experimental results for two coils with an excitation signal of up to 10MHz.\nThe results showed that the equation presents good accuracy for geometric parameters that do not lead the solution of the elliptic\nintegral of the first kind to infinity.
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