This antenna is used to filter the call frequencies of mobile phones. YBCO is a superconductor made from yttrium, barium, copper and oxygen. Superconductors are materials which offer zero resistance to the pasage of an electric current when cooled to below a certain critical temperature. With early superconductors this was only a few degrees Kelvin (K), meaning that they had to be cooled using liquid helium, which is expensive and difficult to handle. In the 1980s, so-called high-temperature superconductors were discovered, including YBCO, which has a critical temperature of 92 K (-181 C), allowing the use of liquid nitrogen instead of helium. Today, superconductors with critical temperatures as 'high' as 150 K (-123 C) have been developed.
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