A method or apparatus for wireless transferring energy between a source coil and a drain coil, comprises selling an initial resonant frequency of the source coil as a first condition; setting the source coil and said drain coil in positions relative to each other to define an initial coupling coefficient therebetween, so that the initial coupling coefficient comprises a second condition; and adiabatically changing one or both of the conditions while pumping energy into the source coil. The source coil energy is transferred to the drain coil over the course of the adiabatic change.