A method of transferring energy comprising: providing a first resonator structure receiving energy from an external power supply, said first resonator structure having a first resonant frequency (ω 1 , a resonance width Γ 1 , a first Q-factor Q 1 , and characteristic size L 1 , providing a second resonator structure being positioned distal from said first resonator structure , at distance D, said second resonator structure having a second resonant frequency ω 2 , a resonance width Γ 2 , a second Q-factor Q 2 , and characteristic size L 2 , transferring energy non-radiatively between said first resonator structure and said second resonator structure , said energy transfer being mediated through coupling of their resonant-field evanescent tails, and the rate of energy transfer between said first resonator and said second resonator being denoted by κ, wherein non-radiative means D is smaller than each of the resonant wavelengths λ 1 and λ 2 , wherein c is the propagation speed of radiation in the surrounding medium, and characterised in that Q 1 > 200 _ and Q 2 > 200 , and κ / sqrt Γ 1 ∗ Γ 2 > 2 , wherein said first resonator structure comprises a capacitively-loaded conducting-wire loop, where the characteristic size L 1 is the radius of the loop, wherein said second resonator structure comprises a capacitively-loaded conducting-wire loop where the characteristic size L 2 is the radius of the loop, wherein the distance D is the center-to-center distance between the first and second resonators, wherein the second resonator structure is part of a mobile wireless receiver, and wherein the mobile wireless receiver is any of a robot, a vehicle, or a computer. providing a first resonator structure receiving energy from an external power supply, said first resonator structure having a first resonant frequency (ω 1 , a resonance width Γ 1 , a first Q-factor Q 1 , and characteristic size L 1 , providing a second resonator structure being positioned distal from said first resonator structure , at distance D, said second resonator structure having a second resonant frequency ω 2 , a resonance width Γ 2 , a second Q-factor Q 2 , and characteristic size L 2 , transferring energy non-radiatively between said first resonator structure and said second resonator structure , said energy transfer being mediated through coupling of their resonant-field evanescent tails, and the rate of energy transfer between said first resonator and said second resonator being denoted by κ, wherein non-radiative means D is smaller than each of the resonant wavelengths λ 1 and λ 2 , wherein c is the propagation speed of radiation in the surrounding medium, and characterised in that Q 1 > 200 _ and Q 2 > 200 , and κ / sqrt Γ 1 ∗ Γ 2 > 2 , wherein said first resonator structure comprises a capacitively-loaded conducting-wire loop, where the characteristic size L 1 is the radius of the loop, wherein said second resonator structure comprises a capacitively-loaded conducting-wire loop where the characteristic size L 2 is the radius of the loop, wherein the distance D is the center-to-center distance between the first and second resonators, wherein the second resonator structure is part of a mobile wireless receiver, and wherein the mobile wireless receiver is any of a robot, a vehicle, or a computer. <EOS>