page_title: Pole piece
section_title: Shapes and forms
hierarchical_section_title: Pole piece / Shapes and forms
caption_attribution_description: English: A "horseshoe" magnet made of Alnico, an alloy of iron, aluminum, nickel, and cobalt. Probably around 1 inch (3 cm) long. It is made in a "horseshoe" shape to bring the North and South poles of the magnet close together, creating a strong magnetic field between them. The metal plate between the poles at bottom is called a "keeper". It is left on the magnet when not in use, to prevent the magnet becoming demagnetized. By creating a closed magnetic circuit, it strengthens the magnetic flux in the magnet, making it harder for mechanical shocks or high temperatures to randomize the magnetic domains of the metal.
context_page_description: A pole piece is a structure composed of material of high magnetic permeability that serves to direct the magnetic field produced by a magnet. A pole piece attaches to and in a sense extends a pole of the magnet, hence the name.
  Pole pieces are used with both permanent magnets and electromagnets. In the case of an electromagnet, the pole piece or pieces simply extend the magnetic core and can even be regarded as part of it, particularly if they are made of the same material. In the case of a permanent magnet, the distinction between the magnet itself and the pole piece or pieces is more clear cut.
context_section_description: Pole pieces take many shapes and forms depending on the application.
  A traditional dynamic loudspeaker has a distinctive annular magnet and pole piece structure which serves to concentrate the magnetic flux on the voice coil. The central, cylindrical pole piece surrounded by the voice coil is normally referred to as the pole piece. A second pole piece in turn surrounds the voice coil.
  A moving coil meter has a different and equally distinctive structure.
  A magnet keeper is a specialised pole piece used to temporarily connect the poles of a permanent magnet, to help to preserve the magnetism, and for safety in the case of large and powerful magnets.
  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.
caption: A horseshoe magnet with a keeper in use
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