Switchable magnet
For switchable magnets with permanent magnets from z. B. Neodymium-Iron-Boron are constructions that, similar to an electromagnet , allow to switch between two magnetic states.
The best known are magnetic feet and lifting magnets . In both cases, a switch or lever is used to turn a magnet, so that the magnetic flux in the construction changes. When switched on, the magnetic flux passes over the pole shoes . When switched off, the flux is diverted internally so that the field lines do not run over the pole shoes.
A typical structure consists of two outer magnets and a central, rotatable magnet with the axis of rotation parallel to the load (see sketch). When switched off, the north and south poles of the pole pieces face each other so that the magnetic field is passed through the magnets there and there is only a very weak magnetic field outside. When switched on, with the central magnet rotated by 180 °, the north pole of both the fixed and the rotatable magnet are arranged on one pole piece, and the south poles on the other, so that a strong magnetic field exists between the pole pieces.
In an alternative arrangement, a second magnet is rotatably arranged parallel to one magnet, with the axis of rotation perpendicular to the load. If the same poles are on one side, there is a strong magnetic field that can be diverted via the pole pieces. If, after turning 180 °, there is a north and a south pole on one side, the external magnetic field is very much reduced.
There are also arrangements in which several smaller magnet systems are moved, for example a base with several magnets over which a disk with several magnets is rotated. The advantages mentioned are the lower weight of the switchable magnet, the lower decrease in the holding force for thin materials and the lower need for neodymium-iron-boron.
For amplification and weakening by differently oriented magnets, see also Halbach array .
An important parameter is the holding force, which is specified in Newtons (N). It has become common practice to also specify a force in kg. The conversion factor is the acceleration due to gravity (9.81 m / s², i.e. 9.81 N corresponds to 1 kg).
The specified adhesive forces are only achieved if the magnetic base is completely seated on a flat or cylindrical (V-base) surface. Bumps interrupt the magnetic flux at these points (magnetic lines emerge) and reduce the adhesive force. So you can z. B. with a corrugated or profiled sheet no longer count on the full adhesive force.
Individual evidence
- ↑ MagSwitch Technology: How MagSwitch Works. June 10, 2015, accessed April 18, 2019 .
- ↑ Patent US8350663 : Rotary switchable Multi-core element permanent magnet-based apparatus. Published January 8, 2013 , Inventor: Jim G Michael.