Can science make true invisibility possible?

A 3D illustration of a metasurface skin cloak made from an ultrathin layer of nanoantennas (gold blocks) covering an arbitrarily shaped object. Light reflects off the cloak as if it were reflecting off a flat mirror.
Xiang Zhang group | University of California Berkely

Several recent studies announced the creation of "invisibility cloaks" — a discovery that should tantalize science fiction fans.

Using a class of man-made substances called "metamaterials," different teams of researchers have independently been able to build tiny (microscopic) cloaks that could make things seem to disappear.

While these experiments have shown measurable results, researchers say that the true invisibility cloaks — such as those seen in the "Harry Potter" films — are still probably a distant dream.

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Metamaterials are ordinary substances, such as metals or ceramics, that are shaped and manipulated in such a way that they take on extraordinary characteristics.

When a person sees an object, the seeing is made possible by the effect of light bouncing off that object and back to your eye. Different surfaces reflect light in different ways, depending on how they are shaped at the microscopic level. The "invisibility" cloaks using metamaterials are designed in such a way that they cancel out the effect of these bumps that allow you to see things. So what you see instead is more like what you would see if you looked into a mirror, or you might just see the space behind the cloak, or nothing at all.

Xiang Zhang and fellow researchers at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory constructed a microscopic sheet made up of nanoscopic gold blocks that does exactly this.

The team used computer models to determine how the tiny gold blocks should be shaped and arranged into the pattern they would need to mask a particular object. They then had the sheet manufactured, and tested it. When the researchers activate the sheet, it cloaks the object behind it, as seen in the video below.

"The reason I can see you is that your face and body have different shapes and different heights — a nose, a chin, and they cast different shadows," Zhang told CNBC. "But I can design the cloak so that it reflects light in such a way that it erases those differences in height and in shape. So what you see is a flat surface."

Boubacar Kante, a researcher at the University of California, San Diego, build a model that shares similarities to the Berkeley model, but is made with ceramics instead of metals.

Kante said that his device could be used to cloak something from radar, and he told CNBC his team has already signed a patent for its technology.

"The idea is that if you have a bump on the street, you can cloak it, and the bump will just look like flat ground," Kante said. "We wouldn't want to do that on the street, since it would cause a lot of accidents. But you can hide something, you can make it look like something else."

David Smith, a professor at Duke, who conducted some of the first successful experiments in invisbility with metamaterials, calls Zhang's study a "tour de force," but adds that it is not quite the same sort of "invisibility cloak" one might wear at Hogwarts.

"The actual 'Harry Potter' cloak, or the sort of thing you see in 'Predator,' or 'Star Trek,' is a long ways off," Smith told CNBC.

For one thing, these cloaks are not adaptive — they have to be custom-made to suit a particular object in a particular position. Once the object moves, the cloak can no longer properly hide it. Zhang said you can build a cloak in a shell-like design, that would cloak any object of whatever shape you could fit under it.

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That's not the only limitation: "You can write out the recipe for this and all of the equations will work perfectly," but translating that recipe into a physical model presents challenges, Smith said.
The materials used can have small effects that can make physical models behave differently than theoretical ones.

Smith noted that his own experiments using metamaterials to create the first invisibility cloak back in 2006 received an almost "over the-top" amount of attention.

Smith is working on commercializing metamaterials for other applications, and said several medium- to large-sized companies are beginning to explore the technology for satellite communications, radar, cellular technology and others. Smith is interested in trying to use metamaterials to transfer power wirelessly from one device to another.

He joined Bellevue, Washington-based Intellectual Ventures in 2013 to that end. Smith is on the advisory board of Kymeta, which was spun off from Intellectual Ventures and focuses on commercial applications for metamaterials, including communications.