ABSTRACT
A permanent magnet (PM) can produce a magnetic field in an air gap with no field excition winding and no dissipation of electric power. External energy is involved only in changing the energy of the magnetic field, not in maintaining it. As any other ferromagnetic material, a PM can be described by its B-H hysteresis loop. PMs are also called hard magnetic materials, meaning ferromagnetic materials with a wide hysteresis loop.
