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A contactless charging system based on a circular coil configuration is presented for electric vehicles. An analytical model of the charging system is derived and used to investigate the effect of system dimensions on the system mutual inductance. The efficiency of the system is then calculated and used as a criterion to optimize the dimensions of transmitter and receiver coils in an uncompensated system, as well as series and parallel compensated systems. As a result, several design rules are presented. Following these rules, it is shown that significant improvement in the system efficiency is achieved by optimizing the coil dimensions while the length and weight of coils are kept constant. The performances of the optimized systems are evaluated using the 3-D finite-element method (FEM) and experiments. The FEM and experimental results are in good agreement, confirming the validity of the analytical model and the optimization approach.