A three-coil electromagnetic induction power transfer system is disclosed for epiretinal prostheses and other implants. A third, buffer coil is disposed between an external transmitting coil and a receiver coil buried within the body to improve efficiency and robustness to misalignments. One or more of the coils can be manufactured using micromechanical machining techniques to lay out conductors in a ribbon of biocompatible insulator, folding lengths of the insulated conductor traces longitudinally over one another, and then spiraling them into a ring. The traces change axial position in the ring by shifting across fold lines. One or more U-shaped sections on the traces can be folded so that adjacent traces can project opposite one another, lengthening the resulting ribbon that can be wound into a coil.