Cloak's on you: Scientists create 'invisible' object

By scattering microwaves with plasmonic materials, University of Texas researchers achieve "three-dimensional cloaking," one step closer to rending something transparent in visible light.

This image demonstrates at which frequencies the 3-D cloaking experiment worked successfully, with the third band showing the upper range of the microwave scattering.

It's not quite the Invisible Man, but researchers say they have gotten a step closer to creating a "three-dimensional cloak" that would render objects invisible.

Scientists at the University of Texas in Austin today said they have hidden a cylinder from microwaves, demonstrating cloaking of an object in free space, rather than a two-dimensional image. The group has not been able to scatter visible light, but it expects that cloaking small objects is possible.

"Cloaking small objects may be exciting for a variety of applications. For instance, we are currently investigating the application of these concepts to cloak a microscope tip at optical frequencies. This may greatly benefit biomedical and optical near-field measurements," said University of Texas assistant professor Andrea Alu in a statement. He is co-author of a paper published today in the Institute of Physics and German Physical Society's New Journal of Physics.

Researchers for years have been designing synthetic materials to coat an object and make it appear transparent. In its experiment, the University of Texas group covered a cylinder with a shell coated with a nanometer-sized plasmonic material that scatters light and other electromagnetic waves.

When we see an object, our eyes receive the reflection of light rays off that object and our brain processes that visual information. At certain frequencies, plasmonic materials can excite electron oscillations that make the light waves scatter in a way that counteracts the normal reflection, according to the University of Texas. The effect is to make it appear transparent.

The paper says that the plasmonic materials work regardless of the shape of the object and, in principle, could work on a broader range of frequencies, including visible light. But there appear to be some limitations on what sorts of materials it will work on. The experiment worked on a dielectric object but not on metals, according to a description from the University of Texas.

In the future, though, portions of aircraft could be covered or optical instruments could use the material to correct effects. "We believe that our results pave the way to realistic, practical applications of 3D stand-alone cloaks for radar evasion and non-invasive radio frequency probing," according to the paper.

Correction at 9:15 a.m: Andrea Alu's gender has been corrected.

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