Researchers find new uses for flexible superconductors

0 Comments | Insight on the News, Jan 15, 1996 | by Hank Hogan

Step by step, researchers are mastering the remarkable ceramic materials that conduct electricity with no resistance -- ushering in a new era in the energy and electronics industries.

The discovery of high critical-temperature superconductors in the mid-1980s led to predictions of levitating trains, speedy computers and advanced medical equipment. Time has passed, and so far HTc superconductors have resisted efforts at commercialization.

That may be about to change. The first commercial HTc superconductors -- used to develop magnetic sensors for medical imaging and laboratory measurements -- are on the market. Compact, highly efficient superconducting electronic filters -- key components in central switching points for cellular communication -- promise dramatically improved wireless communication. A 1,000-horsepower superconducting motor is scheduled to debut in 1998, and a 10,000-horsepower model is on the drawing boards.

"It took many years for the transistor [invented in 1948] to reach widespread applications [in integrated circuits in 1961]"' says Joseph Madden, applications engineering manager for California-based Superconductor Technologies. Like the semiconductors used for making transistors, superconductors have properties markedly different from those found in everyday insulators and conductors.

"A superconductor is a material that does two things," explains Paul Grant, executive scientist at the Electric Power Research Institute in Palo Alto, Calif. "It carries electricity perfectly... It is also a perfect shield against magnetism," which allows one superconductor to float above another.

How can something have no electrical resistance? "Although theoreticians have since diligently pursued a theory to explain HTc superconductors, so far no one theory is the clear winner," notes Balu Balachandran, director of the High Temperature Superconductivity Program at Argonne National Laboratory in Illinois.

Despite the lack of theoretical understanding, however, research scientists, both academic and industrial, have been engaged in intense experimentation with HTc superconductor materials. One of the first problems they encountered: Superconductors, made of brittle ceramics, are ill-suited to form the flexible wires required for most electronic applications.

"If you take ceramic dinner plates and try to draw them into wire, that's very, very challenging processing," says Wei-Kan Chu, deputy director of research for the Texas Center for Superconductivity at the University of Houston. After attempts to machine the new ceramics had proven unsuccessful, two alternate processing approaches were adopted.

In one, borrowed from the semiconductor industry, researchers are developing thin superconducting films ranging from a few tenths of a micron (a millionth of a meter) up to 1 micron, which are patterned through photolithography. This method cuts both processing and material cost. As an added benefit, it allows superconductors to be more easily integrated into standard semiconductor electronics.

In the other method, powered precursor elements are packed into thin silver tubes and treated with heat and oxygen. In this way, it is possible to manufacture superconducting wire or tape that is both flexible and durable, although the wires lose their super-conductivity when exposed to a high magnetic field.

Until recently, the two approaches have not crossed paths. Researchers at the Superconductivity Technology Center at Los Alamos National Laboratory, however, have adapted thin-film processes to build a superconducting tape that is so flexible that it retains its current-carrying ability even if it is wrapped around a pencil. In addition, it is not adversely affected by magnetic fields.

Such superconducting wires could be used for making large transformers that step voltage up and down for transmission through power lines; to replace 30- and 40-year-old power cables underneath most cities; and to generate and store energy.

Experts at the 1994 International Superconductivity Industry Summit predicted the commercial market for superconductors would grow from $1.5 billion in 1993 to $150 billion or more by 2020. Today the market nearly is all low critical-temperature superconductors. LTc superconductors already are used in medicine to detect tumors, in aviation to detect hidden cracks and corrosion, and in a number of other applications.

But these devices are bulky and expensive because of the equipment needed to cool them to a temperature of -454 [degrees] Fahrenheit (-269 [degrees] Celsius). HTc superconductors would be cheaper and smaller. "Instead of using a refrigerator the size of a desk, we can use a refrigerator that's the size of a quart bottle of milk and really achieve the same circuit performance," says Maden. The reduction in size of the supporting equipment opens the possibility for portable diagnostic units and inspection machines.

Both the U.S. and Japanese governments are spending about $200 million a year on superconductor research, and European countries also spend heavily in this area, not to mention private investment. More and more, policymakers are recognizing that superconductors are no longer just a laboratory curiosity.