Researchers in the US have, for the first time, cloaked a three-dimensional object standing in free space, bringing the much-talked-about invisibility cloak one step closer to reality.
Published today, 26 January, in the Institute of Physics and German Physical Society’s New Journal of Physics, the researchers used a method known as “plasmonic cloaking” to hide an 18-centimetre cylindrical tube from microwaves.
Sure, researchers have already made marked strides toward making objects unseeable. But much of the work was more like mimicry: Meta-materials that bent light around an object to conceal it, but only worked in two dimensions. Or a device that played tricks on the eye, by harnessing the mirage effect to make objects behind it “disappear.”
Now, a team of researchers have taken an incredible leap forward. They’ve successfully made a 3-D object disappear.
Metamaterial cloaking is the scientific application of metamaterials in order to achieve invisibility-cloaking. This is accomplished by manipulating the paths traversed by light through a novel optical material. Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum and demonstrate the potential to render an object seemingly invisible. Metamaterial cloaking, based on transformation optics, describes the process of shielding something from view by controlling electromagnetic radiation. Objects in the defined location are still present, but incident waves are guided around them without being affected by the object itself.
To cloak an 18 cm (7 in) long, 2.5 cm (0.9 in) diameter cylindrical
tube from microwaves, the team shelled it in a plasmonic metamaterial.
The team says the cloak hid the 3D object for all angles of incidence
and observation. They tested it by directing microwaves towards the
cloaked cylinder and mapping the resulting scattering both around the
object and in the far-field. The cloak worked best when the microwaves
were at a frequency of 3.1 GHz, reducing the scattering of polarized
microwaves by more than 9 dB for a 60-degree range of angles.
But the team says demonstrating the cloaking on a 3D object using visible light is their key challenge.
"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
micrometre-sized objects," said Professor Alù.