Magnetic levitation, maglev, ormagnetic suspension is a method by which an object is suspended with no support other than magnetic fields . Magnetic pressure is used to counteract the effects of the gravitational and any other accelerations. Earnshaw's theorem proves that using only static ferromagnetism it is impossible to stably levitate against gravity, but servomechanisms , the use ofdiamagnetic materials, superconduction , or sys tems involving eddy currents permi t t his to occur. In some cases the lif ting force is provided by magnetic levitation, but t here is a mechanical support bearing little load that provides stability. This is t ermed pseudo-levitation . Magnetic levitation is used formaglev trains , magnetic bearings and for product display purposes. Lift Magnetic materials and systems are able to attract or press each other apart or to gether with a force dependent on the magnetic field and the area of the magnets, and a magnetic pressure can then be defined. The magnetic pressure of a magnetic field on a superconductor can be calculated by: where Pmagis the force per unit area in pascals , B is the magnetic field in teslas, and 0 = 4×10 í7 N·A í2 is thepermeability of the vacuum. [1] [edit] Stability Static stability means that any small displacement away from a stable equ ilibrium causes a net force to push it back to the equilibrium point. Earnshaw's theorem proved conclusively that it is not possible to levitate stably using only static, macroscopic, paramagnetic fields. The forces acting on any paramagnetic object in any combination ofgravitational , electrostatic, and magnetostatic fields will make the object's position unstable along at least one axis, and can be unstable along all axes. However, several possibili ties e xist to make levitation viable, for example, t he use of electronic stabilization ordiamagnetic materials (since relative magnetic permeability is less than one [2] ); it can be shown that diamagnetic materials are stable along at least one axis, and can be stable a long all axes. Dynamic stability occurs when the levitati on system is able to damp out any vibration-like motion that may occur.
