Technology: Superconductors take the noise out of radio communications

日期:2019-02-28 05:13:10 作者:左丘谈鲦 阅读:

HIGH-TEMPERATURE superconductors could benefit communication systems and other signalling devices that work in the radio and microwave sectors of the spectrum. This is the finding of George Peterson of AT&T Bell Laboratories in Murray Hill, New Jersey, who has made resonators using superconducting ceramics. The shape of radio signals from his resonators are between 10 and 100 times as sharp as anything their all-copper counterparts can produce. Resonators are tubes that contain a central wire or coil of conducting material. They are used in devices that generate or receive radio signals. Resonators that work at highly precise frequencies will be particularly useful in radio communications, astronomy, medicine and the military. Peterson thinks that the materials reduce the signal’s noise by a factor of 100 or more, and compress the bandwidth of the resonating frequency by a factor of 10 or more. The result is a much sharper signal. At low frequencies, superconductingresonators can be much smaller than conventional ones. A superconducting 10-megahertz resonator will fit into one hand, whereas an all-copper version would be the size of a barrel, according to Peterson. At high frequencies, however, the difference in size between a conventional resonator and a superconducting one is negligible, he says. He has made resonators for frequencies up to 1.5 gigahertz. No superconductor has zero resistance at radio frequencies, but Peterson says that the ceramics have much lower resistance than copper. Although the power of his resonators is limited – no more than 4 watts – it is enough for most radio receivers. The success of the laboratories’ superconductors is partly due to a process developed by ICI Advanced Ceramics at Runcorn in Britain, which strengthens the normally fragile ceramic superconductors. A group at ICI, led by Derek Birchall, devised the process to strengthen other ceramics, demonstrating the technique by making a spring of cement 10 years ago. In the process, a polymer is mixed with powdered ceramic materials, producing a substance that can be moulded like plastic. Then the polymer is burned off, leaving behind a very strong ceramic. For the superconductors, ICI uses about 20 per cent polymer by volume, so the finished part is about 20 per cent smaller than the mould. Neil Alford, who leads the superconducting work at Runcorn, made both rodsand coils for the AT&T experiments. Sid Saunders, director of commercial development for ICI Advanced Materials at Wilmington in Delaware, said that Alford can make the superconducting material yttrium-barium-copper oxide almost twice as strong as anyone else. This is an important advantage; some samples are so fragile that they cannot even support their own weight. Peterson was impressed when a sample that ICI posted to him arrived intact. Another advantage of Alford’s process is that it yields a smooth surface, improving conductivity at high frequencies. The resonators are not the first electronic components of high-temperature superconductors. ICI made superconducting antennas last year,