Invisibility Cloak Breakthrough: Scientists Cloak 3-D Objects

Scientists create first free-standing 3D cloak

Researchers in the US have, for the first time, cloaked a three-dimensional object standing in free space, bringing the much-talked-about invisibility cloak one step closer to reality.

Published today, 26 January, in the Institute of Physics and German Physical Society’s New Journal of Physics, the researchers used a method known as “plasmonic cloaking” to hide an 18-centimetre cylindrical tube from microwaves.

Invisibility's Next Frontier: Scientists Cloak 3-D Objects | Danger Room | Wired.com

Sure, researchers have already made marked strides toward making objects unseeable. But much of the work was more like mimicry: Meta-materials that bent light around an object to conceal it, but only worked in two dimensions. Or a device that played tricks on the eye, by harnessing the mirage effect to make objects behind it “disappear.”

Now, a team of researchers have taken an incredible leap forward. They’ve successfully made a 3-D object disappear.

Metamaterial cloaking - Wikipedia, the free encyclopedia

Metamaterial cloaking is the scientific application of metamaterials in order to achieve invisibility-cloaking. This is accomplished by manipulating the paths traversed by light through a novel optical material. Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum and demonstrate the potential to render an object seemingly invisible. Metamaterial cloaking, based on transformation optics, describes the process of shielding something from view by controlling electromagnetic radiation. Objects in the defined location are still present, but incident waves are guided around them without being affected by the object itself.[1][2][3][4][5]

Scientists make 'invisibility cloak' breakthrough - Telegraph

Those hoping for a Harry Potter-style touch of wizardry will be disappointed however. To the human eye, which can only perceive light in higher frequencies, there would have been no invisibility.
But, say the researchers, the experiment is important proof of a principle that so-called plasmonic meta-materials can achieve a cloaking effect.
A warplane cloaked with such materials could achieve "super-stealth" status by becoming invisible in all directions to radar microwaves, said co-lead investigator Andrea Alu.

Researchers cloak free-standing 3D object using plasmonic metamaterials

To cloak an 18 cm (7 in) long, 2.5 cm (0.9 in) diameter cylindrical tube from microwaves, the team shelled it in a plasmonic metamaterial. The team says the cloak hid the 3D object for all angles of incidence and observation. They tested it by directing microwaves towards the cloaked cylinder and mapping the resulting scattering both around the object and in the far-field. The cloak worked best when the microwaves were at a frequency of 3.1 GHz, reducing the scattering of polarized microwaves by more than 9 dB for a 60-degree range of angles.
But the team says demonstrating the cloaking on a 3D object using visible light is their key challenge.
"In principle, this technique could be used to cloak light; in fact, some plasmonic materials are naturally available at optical frequencies. 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 micrometre-sized objects," said Professor Al├╣.