Stealth aircraft and other top-secret military vehicles of the future may benefit from a new carbon nanotube coating that can render a 3D object flat.
Developed by the University of Michigan, the new coating acts as a “magic black cloth” that conceals an object's three-dimensional geometry and makes it look like a flat black sheet, researchers say.
‘Completely Hide’ 3D Attributes
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.
“You could use it to completely hide any 3D attributes of an object,” said principal investigator Jay Guo, a professor in the university’s Department of Electrical Engineering and Computer Science.
Photos: University of Michigan
|A tank etched out of silicon is viewed without (left) and with carbon nanotube coating.|
“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.”
‘Near Perfect Absorption’
The team’s research shows “near-perfect absorption” with the conformal coating on an arbitrarily shaped surface.
The coating uses a “forest,” or thick layer, of multi-walled carbon nanotubes, which prevents “any detectable light reflection and scattering from the object,” the team reports in “Low-density carbon nanotube forest as an index-matched and near-perfect absorption coating,” published in the current issue of Applied Physics Letters.
To demonstrate the 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.
How it Works
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 that light traveling through air doesn't scatter or reflect when it hits the coating.
|The coating can “completely hide any 3D attributes of an object,” says Dr. Jay Guo, whose team conducted the research.|
Carbon nanotubes are well known for their ability to absorb light—NASA just developed a “super black” coating that absorbs more than 99 percent of light—but the Michigan 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, researchers say.
It could, for example, lead to a new type of camouflaging paint for stealth aircraft. Today’s stealth planes use shape to scatter electromagnetic waves and avoid detection; the new coating could actually absorb the waves.
The coating also holds promise as solar heating device, the team says. 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 carbon nanotube forest can absorb a very wide range of electromagnetic waves,” Guo said.
Theoretically, the coating could be applied to any size object—even something the size of a planet or stars, says Guo.
“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,” Guo said.
“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 university is pursuing a patent for the coating and commercialization partners to help bring it to market.