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A simple equivalent-circuit model is developed for a wireless energy-transfer system via coupled magnetic resonances, and a practical design method is also provided. Node equations for the resonance system are built with the method, expanding on the equations for a transformer, and the optimum distances of the coils in the system are derived analytically for optimum coupling coefficients for high transfer efficiency. In order to calculate the frequency characteristics for a lossy system, the equivalent model is established at an electric-design automation tool. The model parameters of the actual system are extracted, and the modeling results are compared with measurements. Through the developed model, it is seen that the system can transfer power over a midrange of a few meters and that impedance matching is important to achieve high efficiency.
Date of Publication: July 2011