Ummm, wait just a second here. Just because your hypotech paint could be rated in negative-x-ohms-per-square doesn’t show that a given swath could deliver the needed /power/. If my house is a purely resistive 10 ohms and runs on 120 V RMS, then the current needed will be 12 A. I^2R is 1440 W. Your “per-square” analysis would make it appear that a postage stamp of the stuff would work just as well as the 20 by 40 array.

Researchers in the US have developed a carbon fibre composite material which exhibits `negative resistance’ – a phenomenon which essentially means electrons appear to flow the wrong way.

Professor Deborah Chung from the University of Buffalo says that combining the material with conventional composite structures, which have high positive resistance, will produce a material that is a superconductor at room temperature.

The research is aimed at giving electronic function to composite structures used in the aerospace and automotive industries. These materials, which consist of layers of carbon fibres bound together with epoxy resin, normally exhibit large resistance in a direction perpendicular to the carbon fibres.

While carbon fibres themselves are electrically conducting, the polymer matrix is an insulator. But resistance is never infinite because there will always be some contact between fibres of adjacent laminae.

Prof Chung found that, if the composite was made with a curing pressure of above 1.4MPa (200psi), negative resistance could be observed at the junctions where the carbon fibre layers are in contact.

Prof Chung describes her findings as “surprising”, saying that these interfaces are geometrically very complex and the reason for negative resistance is unclear. Energy is needed to get the electrons to jump from one lamina to another but its source is unknown.

One suggested mechanism is based on an imbalance of drifting and diffusing electrons. When a voltage is applied, electrons drift between adjacent lamina which are not electrically connected; electrons then diffuse back to the bottom lamina at the short-circuited regions of the interface.

This diffusion current seems to overshadow the drift current, giving the impression of electrons flowing the wrong way. Prof Chung is now working on the theory that this phenomenon “may be driven by the applied current and the entropy-driven backflow of electrons”.

The discovery was made accidentally, while examining the electrical behaviour of carbon composites as a way of improving damage detection. Prof Chung says the research could result in `smart’ aircraft parts which sense their own strain or automotive parts capable of storing huge amounts of power.

Like silicon, carbon fibres can be doped to be n and p-type semiconductors. The research team has already made np junctions (diodes) and is working on making transistors.

“This is a whole new level of `smartness’ in materials,” she said. “For example, using composite structures as electronic components means electronic capabilities could be spread over a much larger surface area, eliminating the problem of heat dissipation.”

It also means aircraft parts could be made without the need to embed sensors, thus improving mechanical properties.