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Mechanical Project On Magnetic Levitation

Introduction to Magnetic Levitation

Magnetic levitation, maglev, or magnetic suspension is a method by which an object isÂ suspended with no support other than magnetic fields. Magnetic pressure is used toÂ counteract the effects of the gravitational and any other accelerations.

Earnshaw’s theorem proves that using only static ferromagnetism it is impossible toÂ stably levitate against gravity, but servomechanisms, the use of diamagnetic materials,Â super conduction, or systems involving eddy currents permit this to occur.

In some cases the lifting force is provided by magnetic levitation, but there is aÂ mechanical support bearing little load that provides stability. This is termed pseudolevitation.Â Magnetic levitation is used for maglev trains, magnetic bearings and for product displayÂ purposes.

Static stability means that any small displacement away from a stable equilibrium causesÂ a net force to push it back to the equilibrium point.
Earnshaw’s theorem proved conclusively that it is not possible to levitate stably usingÂ only static, macroscopic, paramagnetic fields. The forces acting on any paramagneticÂ object in any combination of gravitational, electrostatic, and magneto static fields willÂ make the object’s position unstable along at least one axis, and can be unstable along allÂ axes. However, several possibilities exist to make levitation viable, for example, the useÂ of electronic stabilization or diamagnetic materials (since relative magnetic permeabilityÂ is less than one,Â it can be shown that diamagnetic materials are stable along at leastÂ one axis, and can be stable along all axes.
Dynamic stability occurs when the levitation system is able to damp out any vibration likeÂ motion that may occur.
For successful levitation and control of all 6 axes (3 spatial and 3 rotational) aÂ combination of permanent magnets and electromagnets or diamantes or superconductorsÂ as well as attractive and repulsive fields can be used. From Earnshaw’s theorem at leastÂ one stable axis must be present for the system to levitate successfully, but the other axesÂ can be stabilized using ferromagnetism.

The primary ones used in maglev trains are servo-stabilized electromagnetic suspensionÂ (EMS), electrodynamics suspension (EDS), and experimentally, Inductrack.
If one moves a base made of a very good electrical conductor such as copper, aluminiumÂ or silver close to a magnet, an (eddy) current will be induced in the conductor that willÂ oppose the changes in the field and create an opposite field that will repel the magnetÂ (Lenz’s law). At a sufficiently high rate of movement, a suspended magnet will levitateÂ on the metal, or vice versa with suspended metal. Litz wire made of wire thinner than theÂ skin depth for the frequencies seen by the metal works much more efficiently than solidÂ conductors.

An especially technologically-interesting case of this comes when one uses a HalbachÂ array instead of a single pole permanent magnet, as this almost doubles the field strength,Â which in turn almost doubles the strength of the eddy currents. The net effect is to moreÂ than triple the lift force. Using two opposed Halbach arrays increases the field evenÂ further.
Halbach arrays are also well-suited to magnetic levitation and stabilization of gyroscopesÂ and electric motor and generator spindles.