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  • ‘Metascreen’ Forms Ultrathin Invisibility Cloak

Photonics.com
Mar 2013
AUSTIN, Texas, March 26, 2013 — A new ultrathin Harry Potter-style invisibility cloak can hide three-dimensional objects from microwaves while in their natural environment, in all directions and from all of the observers’ positions.

Most invisibility cloaks up to this point have been large, cumbersome contraptions. The University of Texas at Austin cloak, however, uses an ultrathin layer called a “metascreen” that was fabricated by attaching strips of 66-µm-thick copper tape to a 100-µm-thick, flexible polycarbonate film in a fishnet design.


Experimental setup for the far-field measurement of the cloaked cylinder. Courtesy of "Demonstration of an ultralow profile cloak for scattering suppression of a finite-length rod in free space," JC Soric et al, 2013 New J Phys, 15 033037 doi:10.1088/1367-2630/15/3/033037.

In tests, the material was used to cloak an 18-cm cylindrical rod from microwaves and showed optimal functionality with 3.6-GHz microwaves over a moderately broad bandwidth. In addition, the metascreen’s inherent conformability and the proposed cloaking technique’s robustness will make it possible to cloak oddly shaped and asymmetrical objects, the researchers predict.

Previous cloaking studies have used metamaterials to divert, or bend, the incoming waves around an object. The new method, which the researchers have dubbed “mantle cloaking,” uses the 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 study co-author and professor Andrea Alu. “The advantages of the mantle cloaking over existing techniques are its conformability, ease of manufacturing and improved bandwidth. 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.”


Snapshot in time of the normal electric field distribution for the azimuthal plane. A microwave horn illuminates each test scenario with a TM-polarized Gaussian wavefront at normal incidence. Courtesy of JC Soric et al, doi:10.1088/1367-2630/15/3/033037.

Last year, the same group successfully cloaked a 3-D object using a plasmonic cloaking method, which used more bulky materials to cancel out the scattering of waves.

The investigators will now be looking at the use of mantle cloaking to hide an object from visible light.

“Metascreens are easier to realize at visible frequencies than bulk metamaterials, and this concept could put us closer to a practical realization,” Alu 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 micrometer-sized objects.”

Other possible applications include optical nanotags and nanoswitches, and noninvasive sensing devices for biomedical and optical instrumentation.

The findings were reported in the New Journal of Physics (doi:10.1088/1367-2630/15/3/033037).  

For more information, visit: www.utexas.edu


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