Can’t believe your eyes? Scientists build tiny invisibility cloak
Scientists might be a step – a teeny tiny step – closer to developing that Harry Potter-style invisibility cloak of your dreams. 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 only an object about 1,300 square microns. But the device, described in the journal Science, offers a proof of concept that could potentially be scaled up in the future.
Previous 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 study coauthor Xiang Zhang, a materials scientist at Lawrence Berkeley National Laboratory. “You have to carry a huge cloak around you.”
For this new device, however, the scientists instead decided to scatter the incoming light using a very thin metamaterial – a material whose physical structure, rather than its chemical composition, allow it to manipulate light.
Usually, when light bounces off a three-dimensional object, the light is scattered and the wavefront gets distorted, which is what allows us to see the object’s angles and curves. The new and improved cloak is covered with nanoantennas made of tiny gold blocks of different sizes that can counteract that distortion, making it seem to an observer like the light is coming from a flat surface.
A cloak made out of this metamaterial, just 80 nanometers thick, could one day be used in clothing, Zhang said. The technology could be used, theoretically, to also perform the opposite feat: turning 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, looking to disguise fighter jets as freighters.
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There are also non-military applications: Built into a shirt, cloaking technology might potentially make beer bellies look like six-pack abs. Or it could be used to make a car seem smaller and thus safer, reducing the driver’s blind spots around the vehicle.
Previous cloaks were able only to hide standard objects, like a cylinder. This cloak was able to cover an irregularly shaped object, one with plenty of bumpy bits.
Of course, if you were to make a hypothetical mask out of this metamaterial, it would only work for the particular contours of one individual’s face, and against a predetermined background, Zhang said.
“This cloak may work with your face, but it doesn’t work with my face because our facial features are very different,” he said.
The concept is akin to passive camouflage – but Zhang says he’s hoping to find ways to make it an active system, able to conform to different shapes and work against changing backgrounds.
“That’s the next question – can you make this cloak adaptive?” Zhang said.
The cloak was able to hide an object that was the size of a few biological cells, but Zhang said the concept can be scaled up.
“The work is interesting,” said Boubacar Kante, an electrical engineer at UC San Diego who was not involved in the study. However, the current cloak works only for a discrete wavelength of light - 730 nanometers - and would have to cover more wavelengths to be effective at a larger scale, he said.
Kante also pointed out that there are disadvantages to using metallic particles. Because metals absorb optical wavelengths of light, they actually make what they’re covering seem darker than their surroundings, which can be a dead giveaway. Kante is working on a concept that would use a combination of ceramic particles and teflon to achieve a similar effect.
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