January 26, 2012
Researchers Cloak 3D Objects
University of Texas at Austin researchers have cloaked a three-dimensional object standing in free space for the first time.
The researchers used a method known as plasmonic cloaking to hide a 7-inch cylindrical tube from microwaves. During the study, they were able to show how ordinary objects can be cloaked in their natural environment in all directions and from all vantage points.When using the plasmonic cloaking method, light strikes an object, and rebounds off its surface towards another direction.
Objects are able to be seen because light rays bounce off materials towards our eyes and our eyes are able to process the information.
However, due to their unique properties, plasmonic metamaterials have the opposite scattering effect to everyday materials.
"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," study co-author Professor Andrea Alu said 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 3D object in free-space."
The team cloaked the cylindrical tube with a shell of plasmonic metamaterial to make it appear invisible. The system was tested by directing microwaves towards the cloaked cylinder and mapping the resulting scattering both around the object and in the far-field.
The cloak showed optimal functionality when the microwaves were at a frequency of 3.1 gigahertz and over a moderately broad bandwidth.
The next step for the team will be to demonstrate the cloaking of a 3D object using visible light.
"In principle, this technique could be used to cloak light; in fact, some plasmonic materials are naturally available at optical frequencies," Alu said in a press release. "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."
The research was published in the Institute of Physics and German Physical Society's New Journal of Physics.