Pole piece

[clarification needed] The traditional material for pole pieces was soft iron.

While still often used with permanent magnets, soft iron suffers from eddy currents which make it less suitable for use with electromagnets, and particularly inefficient when the magnet is excited by alternating current.

Another specialised pole piece is the armature of an electromechanical solenoid, which produces work by being attracted by an electromagnet when the magnet is actuated.

An electron lens contains two specialised pole pieces used to guide the electromagnetic field lines of the wire coils of the permanent magnet, these field lines guides the spiral of electrons.

In the objective electron lens an upper annular polepiece surrounds the column and a lower planar polepiece with a 'pinhole' on the optic axis is closest to (adjacent) the object (specimen)