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Concept
Magnetic levitation
Summary
Magnetic levitation (maglev) or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields. Magnetic force is used to counteract the effects of the gravitational force and any other forces.
The two primary issues involved in magnetic levitation are lifting forces: providing an upward force sufficient to counteract gravity, and stability: ensuring that the system does not spontaneously slide or flip into a configuration where the lift is neutralized.
Magnetic levitation is used for maglev trains, contactless melting, magnetic bearings, and for product display purposes.
Magnetic materials and systems are able to attract or repel each other with a force dependent on the magnetic field and the area of the magnets. For example, the simplest example of lift would be a simple dipole magnet positioned in the magnetic fields of another dipole magnet, oriented with like poles facing each other, so that the force between magnets repels the two magnets.
Essentially all types of magnets have been used to generate lift for magnetic levitation; permanent magnets, electromagnets, ferromagnetism, diamagnetism, superconducting magnets, and magnetism due to induced currents in conductors.
To calculate the amount of lift, a magnetic pressure can be defined.
For example, the magnetic pressure of a magnetic field on a superconductor can be calculated by:
where is the force per unit area in pascals, is the magnetic field just above the superconductor in teslas, and = 4π N·A−2 is the permeability of the vacuum.
Earnshaw's theorem proves that using only paramagnetic materials (such as ferromagnetic iron) it is impossible for a static system to stably levitate against gravity.
For example, the simplest example of lift with two simple dipole magnets repelling is highly unstable, since the top magnet can slide sideways or flip over, and it turns out that no configuration of magnets can produce stability.
However, servomechanisms, the use of diamagnetic materials, superconduction, or systems involving eddy currents allow stability to be achieved.
Official source
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