A wireless power transfer system is disclosed. The system includes a first resonator having a first resonant frequency ωo1, a half power bandwidth Δω1, and an unloaded quality factor Qo1=ωo1/Δω1 coupled through a first coupling circuit to a power source, a second resonator having a second resonant frequency ωo2, a half power bandwidth Δω2, and an unloaded quality factor Qo2=ωo2/Δω2 coupled through a second coupling circuit to a load, the first resonator disposed a distance away from the second resonator, wherein the distance is smaller than the first and second resonant wavelengths, the first and second coupling circuits are configured so that up to a maximum achievable power transfer efficiency between the first and second resonators can be achieved, wherein Qo1 and Qo2 can be less than 100.