The Development of ac Rotary Machines [Historical]

After Michael Faraday (1791-1867) produced an electromotive force (EMF) between the axis and edge of a disk kept in rotation and subjected to the axial magnetism of a fixed permanent magnet in 1831, several researchers and experimenters pursued efficient electrogeneration designs capable of replacing expensive electrochemical batteries [1]. It was soon clear that a stronger effect could be achieved with an electromagnetic multiplier (i.e., a coil of many windings) subjected to the alternating action of a permanent magnet, obtained by mutual rotation.