Equivalent circuit characterization of resonant magnetic coupling for wireless transmission of electrical energy

This paper provides the accurate characterization of a wireless power transfer system consisting of two resonant air-core coils mutually coupled in free space. The lumped-circuit parameters of the equivalent circuit are determined with analytical formulas taken from the literature and validated by comparison with numerical simulations with a finite-element computer code and with experiments. The parameters are determined taking as input only the geometry of the system (coil size and mutual distance, conductor radius, and turn distance) and the frequency. Once the lumped-circuit parameters are known with good accuracy, the assessment of the power transfer system can be carried out by evaluating the current and voltage gains and efficiency for different system geometries, operating frequencies and load conditions. The Scilab programming environment was used to perform all the calculations. The characterization presented in this paper can then be considered as an effective tool in designing an efficient wireless power system.