New invisibility cloak hides tiny three-dimensional objects
Source: Dario Borghino

Scientists at UC Berkeley have developed a foldable, incredibly thin invisibility cloak that can wrap around microscopic objects of any shape and make them undetectable in the visible spectrum. In its current form, the technology could be useful in optical computing or in shrouding secret microelectronic components from prying eyes, but according to the researchers involved, it could also be scaled up in size with relative ease.

Objects are visible to us because a small portion of the light that hits them is scattered in the direction of our retinas. Invisibility cloaks can make objects disappear from sight by exploiting the unusual optical properties of so-called metamaterials. These special man-made compounds can manipulate light in unique ways to guide it around the surface of the cloak, so that no light is reflected from it or the object it's shielding.

Cloaks have already been devised that work in the visible, infrared and ultraviolet portions of the electromagnetic spectrum. However, while successful in bending light around an object, these devices also disturb the phase of the electromagnetic wave; so, while the object remains hidden as no light is reflected off it, the cloak itself can still be spotted through specialized instruments. What's more, these devices also tend to be very bulky and hard to scale up in size.

A team led by UC Berkeley's Xiang Zhang has now leveraged significant advances in metamaterial engineering to design an improved cloak that is especially thin (only 80 nanometers thick), does not suffer from the phase detection problems of previous cloaks, works in the visible light spectrum, and could reportedly be scaled up to shield macroscopic objects.





Yuan Wang, Zi Jing Wong and Xiang Zhang have devised an ultra-thin invisibility "skin" cloak that can conform to the shape of an object and conceal it from detection with visible light

The cloak works by using arrays of gold nanoantennas, with each one manipulating the phase of the light wave that is scattered off the cloak. When a cloaked object is illuminated by 730-nanometer wavelength (deep red) light, the antennas make the cloak act like a perfectly flat mirror, regardless of its current shape.

Zhang and team tested their invention by wrapping the cloak around a cell-sized object with a highly irregular shape. As expected, when red light struck the cloak, it reflected off its surface as if off a flat mirror, making the object beneath it invisible even by phase-sensitive detection. When the polarization of the nanoantennas was changed, the cloaking effect stopped entirely.

"This is the first time a 3D object of arbitrary shape has been cloaked from visible light," says Zhang. "Our ultra-thin cloak now looks like a coat. It is easy to design and implement, and is potentially scalable for hiding macroscopic objects."

While the ability to pull a Harry Potter with a large-scale version of this cloak may be years away, the current version could already find use in hiding sensitive layouts of electronic components or aiding the development of optical computers.

A paper detailing the study appears in the journal Science. You can see the cloak in action in the short video below.