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Superconductors are materials that have no resistance to the flow of electricity, as all other substances have. Once merely a scientific curiosity, today’s engineers are searching for new kinds of superconductors that can be made into functional electrical wires or electron devices such as transistors. Resistance to electricity causes energy to be lost as heat. If superconducting materials could be used, this heat would not be generated, so that electricity flowing through wires would not be wasted and devices such as microprocessors would run cooler.
The first superconductor was discovered by Dutch physicist, Heike Kamerlingh Onnes at the University of Leyden. In 1911 he found that mercury lost all its electrical resistance when it was cooled to extremely low temperatures. This intriguing property could not be used in electrical engineering because it was impractical to cool things to such low temperatures. Engineers at Westinghouse managed to make superconducting wire out of the element niobium in 1962, but it was not until 1975 that anyone made use of it—in that year it was used as part of a highly specialized scientific instrument called a particle accelerator.
Superconducting was not only difficult to apply to practical devices, it was also difficult to understand in terms of physics. Interestingly, it was John Bardeen, one of the co-inventors of the transistor, who advanced the first viable theory of superconductivity in 1957. He won a second Nobel Prize for this work. In 1962 Brian Josephson theorized that two currents would flow between two superconducting electrodes even if they were separated by a thin insulator—another strange property of superconductors. This principle was eventually applied to scientific instruments.
Although many new superconducting materials were discovered in the 1980s and 1990s, including many made from ceramics (which are normally used for insulators), the dream of a room-temperature superconductor still seems far off. Today, there are many devices using superconducting materials, but all still must be cooled to extremely low temperatures. The most famous of these is Magnetic Resonance Imaging (MRI), which is used to create images of the inside of the body. Specialized electronic equipment used by cellular telephone providers at their central offices also makes use of superconducting electronic devices known as filters. Electric generator and motor manufacturers such as General Electric (GE) are in the process of building equipment with superconducting materials, which they believe will be successful. Superconducting cables for electric power are still in development, but the longest one in use is just 400 feet long. What are today called “high temperature” superconductors are those capable of operating when cooled by relatively inexpensive means, but they still must be extremely cold, and therefore they are not suitable for everyday technologies. Engineers are hopeful, however, that superconductors will eventually replace conventional materials in many applications.
A current use of superconductors is to make magnetic resonance images (MRIs) of the human body. Powerful magnets made of superconducting material produce fields that penetrate the body, allowing cross sectional images like the one above to be made.