Can’t believe your eyes?
A UC Berkeley team builds an invisibility cloak that may one day hide a fighter jet.
A UC Berkeley team is closer to building an invisibility cloak.
Scientists might be a step — a teeny, tiny step — closer to making a Harry Potter-style invisibility cloak that Muggles can use in the real world.
Researchers at UC Berkeley have created a thin metamaterial that can conform to irregularly shaped objects and render them invisible in certain wavelengths of light.
For now, this cloak is exceedingly small and covers an object that’s only about 1,300 square microns. (A square micron is 1 million times smaller than a square millimeter.) But the device, described in Friday’s edition of the journal Science, offers a proof of concept that potentially could be scaled up in the future.
Previous incarnations of invisibility cloaks tried to gently redirect the light around the object they were hiding. But this required using lots of material, making the cloaks far bulkier than the object they were trying to conceal.
“That is not practical,” said materials scientist Xiang Zhang, director of the NSF Nanoscale Science and Engineering Center at UC Berkeley and senior author of the study. “You have to carry a huge cloak around you.”
So Zhang and his colleagues took a different approach. They decided to scatter the incoming light using a very thin metamaterial — one whose physical structure, rather than its chemical composition, allows it to manipulate light.
Usually, when light bounces off a three-dimensional object, the light is scattered and the wavefront gets distorted. That’s what allows us to see the object’s angles and curves.
The new and improved cloak, just 80 nanometers thick, is covered with nanoantennas made of tiny gold blocks of different sizes. These blocks can counteract that distortion, making it seem to an observer as though the light is coming from a flat surface.
In tests, the cloak was able to hide an object that was the size of a few biological cells, but Zhang said the concept could be applied on a larger scale.
A cloak made of this metamaterial could one day be used to make a thin suit that “you can wear and make yourself disappear,” he said.
In theory, the technology also could be used to make an image stand out instead of hiding it. For instance, Zhang said, it could turn a two-dimensional image into a three-dimensional one. Say hello to holographic television.
It could even be used to make one object look like another, rather than to simply cloak it, he added. That might be useful for the military, which could use the metamaterial to disguise fighter jets as cargo aircraft.
And then there are more whimsical applications: Built into a shirt, cloaking technology has the potential to make beer bellies look like six-pack abs.
Previous cloaks could hide only standard-shaped objects, such as a cylinder. But the world isn’t smooth. This cloak was able to cover an irregularly shaped object, one with plenty of bumpy bits.
The researchers called their device a “skin cloak.” But if you were to make a mask out of this metamaterial, it would only work for the particular contours of one individual’s face, and only against a predetermined background, said Zhang, who is also the director of the materials sciences division at Lawrence Berkeley National Laboratory.
“This cloak may work with your face, but it doesn’t work with my face because our facial features are very different,” he said. “That’s the next question: Can you make this cloak adaptive?”
Boubacar Kante, an electrical engineer at UC San Diego who was not involved in the study, said the skin cloak represents a step forward.
“The work is interesting,” he said.
However, he noted that the cloak works only for a discrete wavelength of red light — 730 nanometers. To be effective at a larger scale, the cloak would have to cover more wavelengths, he said.
Kante also pointed out that there are disadvantages to using gold in an invisibility cloak. Because metals absorb wavelengths of light in the visible spectrum, they make the things they’re hiding seem darker than their surroundings. That could be a dead giveaway.
Kante said he is trying to get around this problem by using a combination of ceramic particles and Teflon to achieve a similar cloaking effect.