Scientists Create Free-Standing 3-D Cloak Invisible to Microwaves

January 29, 2012 Updated: September 29, 2015

The invisibility cloak has taken yet another step toward realization, with U.S. researchers cloaking a three-dimensional object from microwaves for the first time using a technique dubbed “plasmonic cloaking.”

Previous research efforts have demonstrated cloaking two-dimensional (or flat) objects using metamaterials—artificial materials engineered to have special properties—that cause light to bend around them, creating a mirage-like effect.

Plasmonic cloaking differentiates itself with the use of plasmonic metamaterial that causes the scattered light from both the metamaterial and the cloaked object to collide and cancel out. This prevents the reflected light from the object reaching our eyes, making it invisible.

“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 Andrea Alu in a press release.

“One of the advantages of the plasmonic cloaking technique is its robustness and moderately broad bandwidth of operation, superior to conventional cloaks based on transformation metamaterials. This made our experiment more robust to possible imperfections, which is particularly important when cloaking a 3-D object in free-space,” Alu said.

The researchers tested the material by coating a 7-inch cylinder with the plasmonic metamaterial. Microwaves were directed toward the cloaked cylinder and the resultant scattering was mapped. The results confirmed the anticipated performance of the material.

Prior experiments have demonstrated that the material can work with objects of varying shape. The one challenge remaining is to test plasmonic cloaking using visible light.

“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 micrometer-sized objects,” said Alu.

Despite the present theoretical limitations, Alu believes that cloaking small objects could have a range of applications in fields such as biomedical science.

The findings were published on Jan. 25 in the New Journal of Physics.

You can read the research paper here

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