Below Tc, superconducting materials exhibit two characteristic properties:
*Zero electrical resistance
*Perfect diamagnetism (the Meissner effect)
Zero electrical resistance means that no energy is lost as heat as the material conducts electricity
The second of these properties, perfect diamagnetism, means that the superconducting material will exclude a magnetic field - this is known as the Meissner effect (after its discoverer)
Superconducting materials can be categorised into one of two types:
Type I Superconductors - which totally exclude all applied magnetic fields. Most elemental superconductors are Type I.
Type II Superconductors - which totally exclude low applied magnetic fields, but only partially exclude high applied magnetic fields; their diagmagnetism is not perfect but mixed in the presence of high fields. Niobium is an example of an elemental Type II superconductor
commercial use :
1. Magnetic-levitation is an application where superconductors perform extremely well. Transport vehicles such as trains can be made to "float" on strong superconducting magnets, virtually eliminating friction between the train and its tracks. Not only would conventional electromagnets waste much of the electrical energy as heat, they would have to be physically much larger than superconducting magnets.
2.development of a double-relaxation oscillation SQUID (Superconducting QUantum Interference Device) for use in Magnetoencephalography. SQUID's are capable of sensing a change in a magnetic field over a billion times weaker than the force that moves the needle on a compass (compass: 5e-5T, SQUID: e-14T.). With this technology, the body can be probed to certain depths without the need for the strong magnetic fields associated with MRI's
3. An idealized application for superconductors is to employ them in the transmission of commercial power to cities. However, due to the high cost and impracticality of cooling miles of superconducting wire to cryogenic temperatures, this has only happened with short "test runs".
Promising future applications include high-performance transformers, power storage devices, electric power transmission, electric motors (e.g. for vehicle propulsion, as in vactrains or maglev trains), magnetic levitation devices, and Fault Current Limiters.
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