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This paper discusses the use of magnetically coupled resonators for midrange wireless non-radiative power transfer (WNPT). A quasi-static (circuit) model is developed to establish key measures of performance and to aid in design. The use of directly fed, resonant shielded loops for WNPT is also proposed for the first time. Two experimental WNPT systems employing shielded loops are reported. A comprehensive experimental study is performed, and the performance of the WNPT systems shows close agreement with analytical predictions and developed circuit models. With a single-turn system of loop radius 10.7 cm, power transfer efficiency of 41.8% is achieved at a loop separation of 35 cm (3.3 loop radii). When the number of turns is increased to ten, a power transfer efficiency of 36.5% is achieved at a loop separation of 56 cm (5.3 loop radii). Measured magnetic field levels in the vicinity of the WNPT systems are shown to closely agree with analytical field values.