Diamagnetic and eddy current levitation

Diamagnetic and eddy current levitation

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Within the boundaries imposed by our exploration of the technology of levitation and suspension, this chapter addresses diamagnetic phenomena in three categories. These are: 1. Non-metallic materials: In this case, diamagnetism is generally a very weak property that is usually swamped by paramagnetic effects. Biological materials are diamagnetic, very graphically demonstrated by a now famous experiment in which a frog is floated in a powerful magnetic field. The physiological repercussions for the frog are not recorded. 2. Metals: In a non-magnetic environment, 'good' conductors are either weakly diamagnetic or weakly paramagnetic. However, in a changing magnetic field, currents are induced in a conductor. In accordance with Lenz's law, these currents adopt circulation directions that generate secondary fields opposing the original field. In effect, the conductor behaves in a strongly diamagnetic manner. This effect is used widely in levitation systems from bearings to trains. 3. Superconductors: These represent the optimum in diamagnetism by exhibiting a magnetic susceptibility of -1. The strength of the levitation forces available with type I superconductors has provided a new impetus to developments in levitation, although it comes with the disadvantage of the need to provide supercooling. High temperature, type II superconducting materials, within which strong magnetic fields can be trapped, have become a source of very powerful permanent magnets at liquid nitrogen temperatures. This relatively recent development has also given a considerable boost to the search for successful, cost effective levitation systems.

Chapter Contents:

  • 7.1 Diamagnetism
  • 7.1.1 Conventional elements
  • 7.1.2 Compounds
  • 7.2 Eddy currents in metals
  • 7.2.1 Conventional conductors
  • 7.2.2 Lateral displacement
  • 7.2.3 Stabilisation
  • 7.2.4 Levitation through motion
  • 7.2.5 Levitation based on linear induction
  • 7.3 Diamagnetic levitation with superconductors
  • 7.3.1 Electrodynamic levitation
  • 7.3.2 Type II superconductors
  • 7.3.3 Superconduction in transport systems
  • 7.4 Summary
  • 7.5 References

Inspec keywords: permanent magnets; magnetic fluids; magnetic levitation; superconducting materials

Other keywords: circulation directions; biological materials; eddy current levitation; diamagnetic levitation; suspension; superconductors; Lenz's law; levitation systems; conductors; nonmetallic materials; paramagnetic effects; secondary fields; diamagnetic phenomena; permanent magnets; physiological repercussions; magnetic field

Subjects: Magnetic materials; Superconducting materials; Magnetic liquids; Superconducting materials

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