A nanotube coating would allow a plane to absorb a radar beam, making it undetectable.
A new nanostructured coating could be used to make paints for stealth aircraft that can't be seen at night and that are undetectable by radar at any time of day. The coating, made of carbon nanotubes, can be used to cloak an object in utter darkness, making it indistinguishable from the night sky.
Carbon nanotubes have many superlative properties, including excellent strength and electrical conductivity. They are also the blackest known material. The long straws of pure carbon, each just a few nanometers in diameter, absorb a broad spectrum of light—from radio waves through visible light through the ultraviolet—almost perfectly. Researchers are taking advantage of this perfect absorbance in highly sensitive imaging sensors and other prototype devices.
L. Jay Guo, professor of electrical engineering and computer science at the University of Michigan, realized it could be useful as a kind of camouflage. Stealth aircraft, he notes, are often painted black or dark blue to hide them from view.
Guo's group grew sparse forests of vertical carbon nanotubes on the surface of various three-dimensional objects, including a silicon wafer patterned with the shape of a tiny tank. The nanotubes make the objects appear completely flat and black, and they disappear against a black background. The nanotube-coated objects neither reflect nor scatter light.
This effect works, Guo says, because the nanotubes are perfectly absorbing, and because when they are grown with some space between them, as in his experiments, their index of refraction is nearly identical to that of the surrounding air. This means that light won't scatter out of the nanotubes without being absorbed. The work is described in the journal Applied Physics Letters.
Guo says if an airplane painted with the nanotube coating were hit with a radar beam, nothing at all would bounce back, and it would appear as if nothing were there.
Ray Baughman, director of the MacDiarmid NanoTech Institute at the University of Texas at Dallas says.
"This type of cloaking is very interesting, especially since they have demonstrated operation in air."
Baughman recently demonstrated that nanotubes can form an invisibility cloak when they're heated up under water. The heat from a sheet of nanotubes affects the optical properties of the surrounding water, creating the illusion of invisibility.
Invisibility cloaks shield objects by manipulating incident light so that it simply flows around them. Materials that can achieve this must be made very painstakingly and typically only work with a very narrow spectrum of light—say, microwaves, or red or green light. Nanotubes are relatively easy to make, and work across a broad spectrum.
However, it's not yet practical to grow forests of nanotubes on the surface of an airplane directly—growing such forests is a high-temperature, high-pressure process done in chambers much smaller than an airplane. But Guo says it should be possible to grow the nanotubes on the surface of tiny particles which can then be suspended in paint.
COMMENTARY: The 70-micron coating, or carbon nanotube carpet, is about half the thickness of a sheet of paper. It absorbs 99.9 percent of the light that hits it, researchers say.
Jay Guo, a professor in the Department of Electrical Engineering and Computer Science and principal investigator said.
"You could use it to completely hide any 3D attributes of an object. It's not cloaking, as the object can still cast a shadow. But if you put an object on a black background, then with this coating, it could really become invisible."
To demonstrate this concept, the researchers made a raised, microscopic tank shape on a piece of silicon. They then grew the carbon nanotube carpet on top of the entire silicon chip. In photos taken through an optical microscope, they show that the tank is imperceptible. As a control, they did this again, carving out a rectangle that was not coated with carbon nanotubes. The rectangle is visible on this chip, but the tank remains hidden.
Here's how the new coating works: Human eyes perceive an object based on how it reflects or scatters light. The "refractive index" of this new coating is similar to that of air, meaning light traveling through air doesn't scatter or reflect when it hits the coating.
It's well known that carbon nanotubes are capable of absorbing light, but the researchers were able to push it to such a high percentage by spacing them just right.
The "perfect black" material Guo's team created for this coating has a host of varied applications. It could possibly be used in display screens for ultra-high contrast and a crisper picture. It holds promise as solar heating device. The National Institute of Standards and Technology is using a similar material to absorb infrared light and measure the amount of heat it can generate.
The coating could inspire a new type of camouflaging paint for stealth aircraft. Today's stealth planes use shape to scatter electromagnetic waves and avoid detection, and this scheme could actually absorb the waves.
"The carbon nanotube forest can absorb very wide range of electromagnetic wave from ultraviolet up to terahertz," Guo said, "and in principle it can be applied to an arbitrary sized object."
Just how large an object? Guo suggested an intriguing possibility—perhaps entire planets or even stars.
"Since deep space itself is a perfect dark background, if a planet or star were surrounded by a thick, sooty atmosphere of light-absorbing carbon nanomaterial gases, it would become invisible due to the same principle. It would become totally dark to our instruments that rely on the detection of electromagnetic waves. Could this explain some of the missing matter in the universe?"
X-rays or gamma rays would be able to penetrate through the hypothetical "dark veil" Guo proposes. Or, objects behind such veils would cast a shadow by distant stars behind them.
The paper is called "Low density carbon nanotube forest as an index-matched and near perfect absorption coating." Other co-authors are electrical engineering post-doc Haofei Shiand Ph.D. student Hyoung Won Baac and mechanical engineering Ph.D. student Jong Ok. The university is pursuing patent protection for the intellectual property, and is seeking commercialization partners to help bring the technology to market.
In conclusion, this presents serious national security issues if the formula for the nanotube pure black coating ever gets into the wrong hands. I have a feeling that the U.S. military, CIA, and FBI are already all over this technology for their warmongering and spying activities, and making sure nobody other countries, including our allies get their hands on it.
World's Largest Nanotube Manufacturing Plant Announced
CNano Technology (CNano), founded in 2007 to change the economics of producing a wide range of applications based on extremely pure carbon nanotubes, announced today at NT09: Tenth International Conference on the Science and Application of Nanotubes, that it has successfully scaled up its manufacturing technology to reach the world's largest production capacity of 500 tons per year for multiple wall carbon nanotubes. The carbon nanotube products are already in evaluation with selected customers in several markets that include electronics, automotive and energy storage.
Xindi Wu, President and CEO of CNano said.
"This manufacturing capability is an important milestone in the drive to meet current and future customer supply demands. The production line validates our technology at a much larger scale while providing a reliable large volume supply source for customers utilizing the unique properties of carbon nanotubes in their products."
CNano proprietary manufacturing technology enables large scale production at a lower cost structure than other commercial nanotube manufacturing processes. The growing list of commercial applications for carbon nanotubes includes conductive plastics for electronics and automotive, structural composites for sporting goods and aerospace, conductive coatings for displays and aerospace and electrodes for batteries and super capacitors among others.
Tom Baruch, founder and managing director of CMEA Capital, who serves as chairman of CNano said.
"CNano has achieved a truly significant milestone. CNano can now bring mass produced nano materials to market at the right price. The company has broken through a barrier that has existed in this market up until now. They have successfully scaled the manufacturing process for making carbon nanotubes. This now makes their unique combination of elevated mechanical properties and low electrical resistivity available at the low cost necessary for adoption in large consumer and industrial markets."
Peter Liu, Chairman of WI Harper said.
"CNano's management has brought high quality US-style manufacturing into China, tapping the best from both sides of the Pacific Ocean. Through its large scale production of carbon nanotubes, we expect to see more applications that will be feasible that leverage the highly unique properties of this material."
Purnesh Seegopaul, Partner at Pangaea Ventures added.
"This major capacity expansion not only validates CNano's differentiated low cost production capabilities but also now resolves market concerns on price and high volume supply."
CNano platform production technology also facilitates the production of other types of carbon nanotubes. The Company plans to further leverage the 500 ton plant for additional products to be rolled out in the near future.