Scientists claim to have cloaked a three-dimensional object standing in free space, making it invisible from all angles.
At present, the plasmonic cloak is only effective against microwave radiation at a frequency of around 3.1GHz, but the team from the University of Texas at Austin says it could eventually be adapted for visible light.
While previous studies have been either theoretical in nature or limited to the cloaking of two-dimensional objects, the new study shows how ordinary objects can be cloaked in their natural environment, in all directions and from all of an observer’s positions.
Those previous systems also employed inhomogeneous metamaterials that have the ability to bend light around objects. By contrast, the new approach uses plasmonic metamaterials, whereby light strikes the cloaked object and rebounds off its surface towards another direction, just like throwing a tennis ball against a wall. The researchers were able to hide an 18cm cylindrical tube from microwaves in this fashion.
‘In principle, this technique could be used to cloak light; in fact, some plasmonic materials are naturally available at optical frequencies,’ said Professor Andrea Alu of Arizona, who led the team.
‘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.’