Looking Up – Bob Eklund

‘Perfect Black’ Coating Can Render a 3-D Object Flat, Raises Intriguing Dark Veil Possibility in Astronomy —

A carbon nanotube coating developed at the University of Michigan acts as a “magic black cloth” that conceals an object’s three-dimensional geometry and makes it look like a flat black sheet.

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 3-D attributes of an object,” said Jay Guo, a professor in the Department of Electrical Engineering and Computer Science and principal investigator.

“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.”

A paper on the research is newly published online in Applied Physics Letters.

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 the absorption to such a high percentage by spacing the nanotubes 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 also holds promise as solar heating device, creating heat from light. The National Institute of Standards and Technology is testing this by using a similar material to absorb infrared light and measure the amount of heat it can generate.

The coating could also 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 a very wide range of electromagnetic waves, from ultraviolet up to terahertz,” Guo said,


The “perfect black” concept also has several applications in astronomy. It could be used coat the interiors of telescope tubes and other optical devices so as to eliminate internal reflections and scattered light.

Guo also suggests that a similar but natural form of extreme light-absorption, occurring within dust clouds in space, could be hiding 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,” 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?”

How could astronomers detect or see through such nanomaterial clouds? X-rays or gamma rays would be able to penetrate through this hypothetical “dark veil,” Guo proposes. Or, objects behind such veils might cast a shadow in the light of distant stars behind them.

Starshadows? Wasn’t it Shakespeare who wrote (Hamlet, Act I, Scene V), “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy…”?

You can contact Bob Eklund at [email protected], or visit his website at www.bobeklund.com.

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