“An electrical machine is an electromagnetic energy conversion device. It translates its input electrical power into an output mechanical power. Electrical machines have been available and working for nearly a century (Bose, 1986). During this period many extensive efforts have been made by researchers worldwide to develop and improve design, configuration, and performance of electrical machines. 

Nowadays, electrical machines are found in various physical topologies. They may be categorized according to their conductor geometry and field orientation (see Figure 1) as:

1. Radial-field machine, where the conductor is axial and the airgap flux is radial. 
2. Axial-field machine, where the conductor is radial and the airgap flux is axial.
3. Linear machine, where the mutually perpendicular flux and the conductors are arranged along a linear path.” 
Al-Badi, Gastli, Bourdoucen and Jervase (2000, December). “Evolution of Axial-Field Electrical Machines. Science and Technology.” Special Review (2000) 227–45.

This piece is about the second category. 

Hugo Morales Murguía