John Heritage <xebec@home.com> asked about the negative resistance article which expired off the www.buffalo.edu news server at <URL: http://www.buffalo.edu/news/Latest/ChungResistance.html>. I saved a copy so I though't I'd post it and get it in the list archive.
Release Date:
EMBARGOED UNTIL 7/9/98
Contact: Ellen Goldbaum
Phone: 716-645-2626
E-mail:
goldbaum@newsb.buffalo.edu
SUPERCONDUCTION AT ROOM TEMPERATURE:
NEGATIVE ELECTRICAL RESISTANCE SEEN IN
CARBON COMPOSITES
LAS VEGAS -- Materials engineers at the University at
Buffalo have made two discoveries that have enabled
carbon-fiber materials to superconduct at room temperature.
The related discoveries were so unexpected that the researchers
at first thought that they were mistaken.
Led by Deborah D.L. Chung, Ph.D., UB professor of mechanical
and aerospace engineering, the engineers observed negative
electrical resistance in carbon-composite materials, and zero
resistance when these materials were combined with others that
are conventional, positive resistors.
Their observation of zero resistance is the first time that this has
been seen without cooling. Zero resistance has been seen in
superconducting materials, but only at temperatures of 125
degrees Kelvin, about -150 degrees Centigrade or -234 degrees
Fahrenheit.
Without resistance, there is no energy loss, so the amount of
energy that is put into a system is exactly the amount that it
produces.
According to the researchers, the discovery has the potential to
lead to much faster, far- more-efficient electronic devices,
previously assumed to be possible only with the development of
room-temperature superconductors. Potential applications
include much-simpler, more-powerful electronic circuits in
computers and far-more-efficient "smart" structural
components for aircraft and concrete structures.
The research was presented here today (July 9, 1998) in a
keynote address at the fifth International Conference on
Composites Engineering by Chung, who holds the Niagara
Mohawk Chair in Materials Research at UB.
"We have achieved zero resistance without cooling and without
a superconducting material," said Chung.
"With structural electronics, the structural composite itself can
act as the electrical circuitry, but the fibers in the composite are
far less conductive than copper. Our research shows that it is
possible to overcome that resistance and make these structural
electronics far more efficient," she said.
This finding of negative resistance flies in the face of a
fundamental law of physics: Opposites attract.
Chung explained that in conventional systems, the application of
voltage causes electrons -- which carry a negative charge -- to
move toward the high, or positive end, of the voltage gradient.
But in this case, the electrons move the other way, from the plus
end of the voltage gradient to the minus end.
"In this case, opposites appear not to attract," said Chung.
The researchers are studying how this effect could be possible.
Chung, working with Shoukai Wang, a UB doctoral candidate in
mechanical and aerospace engineering, made the discovery
while conducting research on the intrinsic electrical properties of
carbon composites related to developing "smart materials," in
which she has played a leading role.
Chung explained that it is the unusually high pressure used to
cure the carbon-epoxy composite that appears to be responsible
for the finding.
"We were looking at the effect of curing pressure on the junction
between carbon-fiber layers, and were making electrical
measurements of the interface," she said. "When we saw the
negative resistance at the interface, we didn't believe it for quite
a few months. But after checking and rechecking our
connections, using different meters over a period of time and
observing the continuous change of resistance from positive to
zero and then to negative values during curing, we came to
realize that what we were seeing was truly negative resistance."
According to Chung, an unknown mechanism must be at work
that is being triggered by sufficient contact between the layers of
carbon fibers.
In the experiments, two layers of carbon fibers oriented in
different directions and bound together by epoxy, Portland
cement or pressure demonstrated negative resistance as low as
-8 ohms for a contact area of one square centimeter. (An ohm is
a unit that measures electrical resistance.)
The researchers noted that absolute zero resistance can be
achieved when the values of positive and negative resistors
connected in series match exactly.
"It's a matter of tailoring them to make them exactly the same,"
said Chung.
A patent application has been filed on the invention.
Previous patents filed by other researchers on negative resistance
have been limited to very narrow ranges of the voltage gradient.
In contrast, the UB researchers have exhibited negative
resistance that does not vary throughout the entire gamut of the
voltage gradient.
Companies that are interested in technical information on the
invention should contact the UB Office of Technology Transfer
at 716-645-3811 or by e-mail at
lohrman@research.buffalo.edu.