Scientists make 'invisibility cloak' breakthrough Plasmonic meta-materials are composites of metal and non-conductive synthetics made of nanometre-sized structures that are far smaller than the wavelength of the light that strikes them. As a result, when incoming photons hit the material, they excite currents that make the light waves scatter. The new experiment entailed making a shell of plasmonic meta-materials and placing the cylinder inside, and exposing the combination to microwaves. Microwaves scattered by the shell ran into microwaves bounced from the object, preventing them sending a return signal to the viewer. "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 observations," said Alu. Any shape of object can be masked, he added. The cloaking worked best at a microwave frequency of 3.1 gigahertz, said the paper. The feat is a step forward because other techniques have entailed bending light around two-dimensional objects or, in 3D, masking microscopic bumps on mirrors or reflectors, an approach called "carpet cloaking," say the authors. The new concept could be modified for visible light, although any cloaked objects would be very small, in the micrometer range, as the plasmonic effect is linked to the wavelength of the light, Alu said in a phone interview. Even so, there could be important applications for microwave meta-materials, he said. "Camouflaging to radar is one important application, a super-stealth device to make objects invisible to radar," he said. What we are thinking about is not necessarily cloaking the whole warplane but some hot spots, a part such as the tailplane that you would want to cloak because it reflects most of the energy (from microwave radar). Another outlet would be in laboratories, filtering out the "backscatter" of light from the tip of high-powered optical microscopes. Unwanted light such as this impairs images of the object that is being scrutinised, and skews measurements.