Covers that can do more
Carbon-based composites are popular materials for designers of airplanes, automobiles and other high-tech goods because of their strength and light weight. They may become even more popular in the future because a technician has discovered an intriguing new property of the composites: they can conduct electricity like a semiconductor. "This is a whole new level of 'intelligence' in building materials," said Deborah Chung, professor of mechanical and aerospace engineering at the University at Buffalo. "We can now use the building material itself as the electronic part." She presented her research on March 4, 1998 at the International Symposium on Smart Structures and Materials in San Diego.
Carbon composites are known for their durability and light weight. They are mainly used to make aircraft parts and are increasingly used for vehicle parts, bridges, machines and sports equipment. Optical or electronic sensors are currently used to detect changes in shape and deformation. For this purpose, they are embedded in carbon composites used in the production of aircraft parts. This process itself can significantly weaken the component in question. "Furthermore," explained Chung, "these devices can only be used in certain places, but not consistently throughout the device."
Therefore, she studied the electrical behavior of carbon composites to improve damage detection. She focused on how to detect temperature changes in the material using the building material itself as an indicator. She discovered that the electrical properties of the composite also changed with temperature.
"This typically indicates a semiconductor," she explained. 'What's even more unusual about this particular material is that it had the properties of a semiconductor in one direction, but appeared metallic in another direction. Normally a semiconductor, such as silicon, is a semiconductor in all directions.' The advantage of having metal and semiconductor in one material is that the metallic properties for the composite provide a system of built in electrical contacts and leads to which a measuring device can be connected.
Using the fibers as conductors and placing an insulator between the layers of fibers also forms a large capacitor, Chung says, allowing an entire airplane or car part made from the composite to store energy. An electronic building material would thus have exceptional potential for energy storage. As a result, an aircraft part can act like a huge solar cell. Solar cars would also be easier to realize since the entire body paneling, made up of carbon composites, could store energy. Even something as exotic as computers without chips would in principle be possible.
Chung plans to focus on the development of optoelectronic and electronic devices made from the composite. She has already applied for a patent for her invention.
The new semiconductor materials are made from carbon-graphite fibers embedded in a polymer matrix. Their production would be simpler and cheaper than silicon-based electronics. The new semiconductors would distribute electronic capabilities over much larger surface areas, and thus thermal conduction - one of the major challenges for all circuit packaging today - would no longer be an issue.
The Heidelberger Verlag Spektrum der Wissenschaft is the operator of this portal. Its online and print magazines, including "Spektrum der Wissenschaft", "Gehirn&Geist" and "Spektrum – Die Woche", report on current research findings.
