Electromagnetic Induction
It is a very basic principle you drive a magnet thru a induction coil the flux creates a voltage. The frequency of change of magnetic flux is what depicts that the ring will produce a constant supply of electromagnetic induced voltage.
Explore Electromagnetic Induction:
Michael Faraday
After Faraday discovered, in 1831, that a changing magnetic field can induce a current, he performed a series of experiments that showed clearly that the induced EMF is equal to the rate of change of magnetic flux.
The ring has several magnetic flux fields and has the potential to be spun thru each individual induction coil at an extreme rate goverened only by the supply voltage to the drive coils.