A device has a plurality of coils arranged along a perimeter within the device, where each coil has a winding configured to be coupled to a power converter through a resonant capacitor, and forms a resonator with the resonant capacitor. The device has also a connection core which is magnetically coupled to the plurality of coils. Furthermore, the device has a plurality of power converters, where each power converter is coupled to one of the plurality of coils, and is configured such that a current flowing through the winding of the coil has the same frequency as other winding currents in the device, and the phase angle of the current is approximately equal to the space angle of the coil, so a rotating magnetic field is formed in a space around the device.