Pole piece
A pole piece is a component made of a material with high permeability , for example iron . It is used to let the magnetic field lines of a permanent magnet or a winding emerge in a defined shape and to distribute them.
In an electric motor , for example, the magnetic excitation field is distributed over the armature in a circular segment by a pole piece . This homogenizes the course of the magnetic flux density along the armature circuit. Not only the stator has pole shoes, but also the armature of DC motors or the rotor of turbo generators . The latter generates the excitation field in an elongated coil that carries pole pieces in order to distribute the field on the cylindrical outer surface of the rotor.
In the case of special designs, such as the linear motor , the pole pieces are not shaped like a segment of a circle, but flat. Instead of a rotating movement, a linear movement is generated.
In electrodynamic loudspeakers , the pole pieces are called pole plates; they generate a radial field in an annular gap.
Pole shoes of the excitation windings of AC motors , rotors of DC motors and wattmeters must be laminated to keep eddy current losses low. For this reason, alternator stators also have sheet metal pole shoes.
An optimized pole piece improves the efficiency of the salient pole machine .