Invisibility cloaks have been made before, but they've always been bulky and cumbersome. Layer upon layer of material was needed to distort incoming and outgoing wavelengths of light and make an object look like the flat surface behind it. Now, scientists have created a thin invisibility cloak using a single-layer sheet.
Invisibility cloaks are used to cover an object and shield it from view while projecting the surface or image behind it. “This cloaking device basically fools the observer into thinking that there’s a flat surface,” said Boubacar Kanté, from the University of California - San Diego, and senior author of the study which was published in Progress In Electromagnetics Research.
“Previous cloaking studies needed many layers of materials to hide an object, the cloak ended up being much thicker than the size of the object being covered,” said Li-Yi Hsu, the first author of the study. “In this study, we show that we can use a thin single-layer sheet for cloaking.”
This new, single-layered cloak distorts light rays that strike it. The distorted light rays look as though they have come from a flat surface. The materials responsible for this effect are a ceramic and Teflon. Together they make a dielectric: a poor conducting material, which has the handy property of not absorbing much light and reflecting most of it. They are tailored at a very small scale to direct reflected light beams in the ways that the scientists need them to go to produce the effect of a flat surface.
It also addresses a problem that some other cloaks failed to correct. Older cloaks would significantly reduce the brightness of the space behind them (which is unsurprising if the light rays needed to travel through many layers of cloak). This is because these previous cloaks used metal particles that absorbed light which made the cloak area dimmer. This single layer has a lower loss in intensity than the previous versions. “Imagine if you saw a sharp drop in brightness around the hidden object, it would be an obvious telltale,” commented Kanté.
In the future, the team wants to achieve a “lossless” cloak that won't reduce any intensity at all when the light is reflected (but its cloaking ability should hopefully leave you at a loss for words).
“Doing whatever we want with light waves is really exciting,” said Kanté. “Using this technology, we can do more than make things invisible. We can change the way light waves are being reflected at will and ultimately focus a large area of sunlight onto a solar power tower, like what a solar concentrator does. We also expect this technology to have applications in optics, interior design and art.”
Central Image: The reflection pattern of an uncloaked object on a flat surface (top) compared with the reflection pattern of the same object covered with the cloaking device (bottom), which effectively mimics the reflection from a completely flat surface. Li-Yi Hsu/Jacobs School of Engineering/UC San Diego.