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| What's Superconductivity? |
(1) Zero Electrical Resistance
The main feature of superconductivity is zero electrical resistance. As shown in the figure on the right, in the case of metals such as copper, when temperature is lowered, resistance will gradually become lower, but it will never reach zero. However, in the case of superconductivity, electrical resistance will reach zero when temperature is below critical temperature. From the viewpoint of industrial applications, this is the most important characteristic. This phenomenon is applied to the superconducting cables currently under development in Sumitomo.
Because superconductors have zero electrical resistance, currents can pass through at high density. Taking advantage of this feature, the superconducting magnets that generate strong magnetic fields are manufactured.
(2) Meissner Effect
When a magnetic field is applied to a superconductor, electric current passes through the superconductor so as to cancel out the magnetic field, thus preventing the magnetic field from entering. This phenomenon is called the Meissner effect. Because no magnetic field enters, strong repulsion is generated between the superconductor and magnet. Some people may have seen the experiment where a black mass of superconductor floats in the air. The trick is that the superconductor repels the magnet and therefore is suspended in midair.
(3) Josephson Effect
When a thin layer of insulator is sandwiched between two superconductors, until the current becomes certain volume, electrons pass through the insulator as if it does not exists. This phenomenon can be applied to the switching devices that conduct on-off operation at high speed.
(4) Quantized Magnetic Flux
Magnetic flux (a batch of magnetism) that flows through the ring of superconductor is an integral multiple of the minimum unit (flux quantum). This phenomenon is called the quantization of magnetic flux. If counting of quantized magnetic is conducted, extremely precise measurement of magnetic field is possible. One of the products to which this principle is applied is SQUID, the sensor that captures very small changes in magnetic generated when the brain and muscles move. Sumitomo Electric Hightechs Co., Ltd. handles development and sales of SQUID.
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