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Researchers create 166μm-thick invisibility cloak

01 Apr 2013

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Researchers at the University of Texas in the United States announced that they have developed an invisibility cloak that is only 166µm thick and can hide 3D objects from microwaves in their natural environment, in all directions and from all of the observers' positions.

The "metascreen" cloak was made by attaching thin strips of copper tape to a flexible polycarbonate film, which is a fraction of a millimetre thick, in a fishnet design. It was used to cloak an 18 cm cylindrical rod from microwaves and showed optimal functionality when the microwaves were at a frequency of 3.6GHz and over a moderately broad bandwidth.

The researchers also predict that because of the inherent conformability of the metascreen and the robustness of the proposed cloaking technique, oddly shaped and asymmetrical objects can be cloaked with the same principles.

Objects are detected when waves—whether they are sound, light, X-rays or microwaves—rebound off their surfaces. The reason we see objects is because light rays bounce off their surfaces towards our eyes, and our eyes are able to process the information.

Mantle cloaking
Unlike previous cloaking studies that have used metamaterials to divert, or bend, the incoming waves around an object, this new method, which the researchers dub "mantle cloaking," uses an ultrathin metallic metascreen to cancel out the waves as they are scattered off the cloaked object.

"When the scattered fields from the cloak and the object interfere, they cancel each other out, and the overall effect is transparency and invisibility at all angles of observation," said Andrea Alú, a co-author and an assistant professor in the Department of Electrical and Computer Engineering.

"The advantages of the mantle cloaking over existing techniques are its conformability, ease of manufacturing and improved bandwidth," Alú said. "We have shown that you don't need a bulk metamaterial to cancel the scattering from an object—a simple patterned surface that is conformal to the object may be sufficient and, in many regards, even better than a bulk metamaterial."


University of Texas invisibility cloak

(Left) Experimental setup for the far-field measurement of the cloaked cylinder. (Right) Near-field measurements comparing the uncloaked cylinder, the cloaked cylinder and a free-space measurement at the design frequency. The top row refers to illumination at normal incidence, the bottom row to oblique illumination at 30 degrees off the axis.


Last year, the same researchers were the first to successfully cloak a 3-D object using a method called "plasmonic cloaking," which used more bulky materials to cancel out the scattering of waves.

Moving forward, one of the key challenges for the researchers will be to use "mantle cloaking" to hide an object from visible light.

"In principle this technique could also be used to cloak light. In fact, metascreens are easier to realise at visible frequencies than bulk metamaterials, and this concept could put us closer to a practical realisation," Alú said. "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.

"Still," Alú said, "we have envisioned other exciting applications using the mantle cloak and visible light, such as realising optical nanotags and nanoswitches and noninvasive sensing devices, which may provide several benefits for biomedical and optical instrumentation."

The paper can be downloaded online.




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