Researchers Make 3D Object Invisible to Microwaves

For the first time ever, a team of researchers from the University of Texas at Austin has cloaked a 3D object standing in free space.

According to the Institute of Physics, the researchers applied a technique known as plasmonic cloaking to hide a cylindrical tube, measuring 18 cm in length and having a radius of 1.25 cm, from microwaves.

Mapping of the electric field distribution around and on top of the tube (Prof. Andrea Alu et al)

Their study, published today in the New Journal of Physics, describes the design, realization and testing of a realistic metamaterial plasmonic cloak tailored to suppress microwave scattering off the tube.

Due to their unique properties, plasmonic metamaterials exhibit optical properties opposite to those of glass, air, and the other materials of our everyday world.

For instance, light traveling from air into water bends upon passing through the normal and entering the water. But light beaming from air toward a plasmonic metamaterial would not cross the normal. Rather, it would bend the opposite way.

“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,” explained Prof. Andrea Alu, a lead author on the study.

“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.”

Assembled cloak on the cylinder with end caps (Prof. Andrea Alu et al)

The next challenge for the researchers is 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. 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 Prof. Alu.

“Still, cloaking small objects may be exciting for a variety of applications. For instance, we are currently investigating the application of these concepts to cloak a microscope tip at optical frequencies. This may greatly benefit biomedical and optical near-field measurements,” concluded Prof. Alu.