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This invisibility cloak is thinner than anything in Harry Potter's closet

These microwave images show how an object looks in normal view (top row) and oblique view (bottom row) when it's uncloaked, and when it's cloaked by a metascreen. A free-space view of the scene is included as well.



If you liked last year's bulky invisibility cloaks, you'll love this year's fashionable ultra-thin invisibility wrap — which is just a tenth of a millimeter thick but can still make the objects inside undetectable to microwave scans.

"This is the first time an ultra-thin cloak has been realized, much thinner than the wavelength," Andrea Alu, a materials-science researcher at the University of Texas at Austin, told NBC News in an email. "The approach is unique."


Invisibility cloaks have been the stuff of science-fiction stories ranging from the "Star Trek" TV series to the Harry Potter sorcery saga, but they're also becoming the stuff of science fact. The first real-life invisibility cloak was created in 2006, and they've gotten a lot better since then.

Alu and his colleagues describe what they call a "3-D stand-alone mantle cloak" this week in the New Journal of Physics. The research builds on past work with bulkier kinds of cloaking devices. The first invisibility cloaks guided light waves around hidden objects. Last year, Alu's group showed how a shell of plasmonic materials could cancel out the scattering of light waves by an object, rendering it invisible. This week's research paper features a new kind of wave-canceling cloak that's much thinner than the shell.

The University of Texas researchers took a 18-centimeter-long cylindrical ceramic rod and wrapped it in what they call a "metascreen," a layer of flexible plastic film overlaid with a fishnet pattern of copper tape. In the visible spectrum, the wrapped-up object looked like a tube of kitchen plastic wrap. But when the researchers beamed microwaves at the object, their microwave imagers couldn't pick up the object's signature.

"The wave can pass through the object, if it is penetrable," Alu explained.

Alu et al. via New Journal of Physics

This image shows the experimental set-up for far-field microwave observations. The cylinder at the center of the scene is a ceramic rod wrapped in an invisibility cloak that's just a tenth of a millimeter thick.

Alu et al. via New Journal of Physics

A near-field experiment demonstrated that the rod wrapped in a copper-and-plastic metascreen was invisible to microwaves, even when the rod was inclined at an angle.

The researchers reported that invisibility effect was present over a moderately broad bandwidth, with optimal performance at a wavelength of 3.6 gigahertz. The same technique could be used to produce invisibility in different wavelengths.

"In terms of applications, radar camouflaging is one," Alu said. He said the technique could defeat advanced countermeasures for stealth radar detection, such as looking for the radar "shadow" of a stealth-concealed object. Alu and a colleague also have proposed a method for terahertz-wave invisibility, which could theoretically make objects invisible to airport security scanners.

Alu said the potential applications aren't limited to stealth and spycraft. "The main civil applications we have suggested for this technology are in the area of non-invasive sensing, biomedical and optical nanodevices for computing, and energy harvesting," he said.

Harry Potter might not want to give his old cloak of invisibility cloak to Goodwill just yet, though. The metascreen constructed by Alu and his colleagues will work only for microwaves, and not for the visible-light wavelengths that our eyes can see.

"In principle, this technique could also be used to cloak light," Alu said in a news release. "In fact, metascreens are easier to realize at visible frequencies than bulk metamaterials, and this concept could put us closer to a practical realization. However, the size of the objects that can be efficiently cloaked with this method scales with the wavelength of operation, so when applied to optical frequencies, we may be able to efficiently stop the scattering of micrometer-sized objects."

That means Harry will still have to keep the bulky old cloak in his closet — unless he can use the "Decresplitudo" spell to shrink himself to a millionth of a meter in size. And if he can do that, who needs a cloak?

More about invisibility:


In addition to Alu, the authors of "Demonstration of an Ultralow Profile Cloak for Scattering Suppression of a Finite-Length Rod in Free Space" include J.C. Soric, P.Y. Chen, A. Kerkhoff, D. Rainwater and K. Melin.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.