Saturday, September 26, 2015

Scientists Build Tiny ‘Cloak Of Invisibility’

LightWaves

Reflected Light: The Berkley Lab writes: “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. ”
Photo Credit: UC Berkeley; Xiang Zhang Group
Source: UC Berkley

A press release, by Lynn Yarris, for Berkley Lab, and reported widely in the science media, says that researchers at Lawrence Berkeley National Laboratory at the University of California, Berkley, have taken the first steps in designing an invisibility cloak, which has been able to hide a tiny object measuring approximately 1,300 square microns in area.

The research project is led by Xiang Zhang, director of materials sciences at the Berkeley Lab and professor at UC Berkeley’s department of mechanical engineering. In “Making 3D Objects Disappear” (September 17, 2015), Yarris writes:
Working with brick-like blocks of gold nanoantennas, the Berkeley researchers fashioned a “skin cloak” barely 80 nanometers in thickness, that was wrapped around a three-dimensional object about the size of a few biological cells and arbitrarily shaped with multiple bumps and dents. The surface of the skin cloak was meta-engineered to reroute reflected light waves so that the object was rendered invisible to optical detection when the cloak is activated.
“This is the first time a 3D object of arbitrary shape has been cloaked from visible light,” said Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division and a world authority on metamaterials—artificial nanostructures engineered with electromagnetic properties not found in nature. “Our ultra-thin cloak now looks like a coat. It is easy to design and implement, and is potentially scalable for hiding macroscopic objects.”It is the scattering of light—be it visible, infrared, X-ray, etc.,—from its interaction with matter that enables us to detect and observe objects.
The rules that govern these interactions in natural materials can be circumvented in metamaterials whose optical properties arise from their physical structure rather than their chemical composition. For the past ten years, Zhang and his research group have been pushing the boundaries of how light interacts with metamaterials, managing to curve the path of light or bend it backwards, phenomena not seen in natural materials, and to render objects optically undetectable. In the past, their metamaterial-based optical carpet cloaks were bulky and hard to scale-up, and entailed a phase difference between the cloaked region and the surrounding background that made the cloak itself detectable—though what it concealed was not.
The cloaking technology comes with an on-off switch, which is what one would expect. After all, the idea behind cloaking is that it is only used temporarily, as needed, for a period of time. Such a cloak is part of science-fiction lore, including Star Trek and more recently a staple of the Harry Potter series. This cloak is microscopic in size, but it is believed that the principle under-girding it would make it work on the macroscopic level.

Equally important to note is that the research has focused on a discrete wavelength of 730 nanometers, which is close to wavelength of infrared light. For the cloak to have marketable commercial applications, it would have to work at much wider wavelengths of the visible spectrum (380 nm to 740 nm). That it can potentially be scalable to large objects and can be used for various wavelengths of the visible spectrum makes this technology useful for both industrial and military use.

But this will not happen soon; the next step is to see if a larger object can be cloaked or hidden using the same engineering principles that worked on the macroscopic level. A more comprehensive article  (“An ultrathin invisibility skin cloak for visible light”; September 18, 2015) can be found in the journal Science.

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For more, go to [Berkley]

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