New invisibility cloak material

A material capable of invisibly cloaking three-dimensional objects has been unveiled by scientists in the US.

For many years, invisibility garments and cloaking devices have been the preserve of Harry Potter and Star Trek. More recently, scientists have begun to tinker with substances called metamaterials, which use physical structures to guide light through themselves in such a way as to make an object clad by the material appear not the be there. But these substances are hard to make, bulky, and able to shroud only very minute structures.

Now, University of California, Berkeley, researcher Xiang Zhang and his colleagues have come up with a new approach which, they claim, is superior, scalable and much simpler to make.

Their material, showcased this week in the journal Science, consists of a magnesium fluoride surface through which project tiny pillars of gold. Measuring about one thousandth of a millimetre across, each pillar acts as a tiny antenna, absorbing light energy and then re-emitting it.

And because the surface is carefully constructed to compensate for the different distances that light would have traveled to bounce off a three-dimensional object, a treated surface just resembles a flat, mirror-like sheet.

A giveaway in previous metamaterial-based invisibility systems was that they introduced what is known as a phase shift in the light waves interacting with the material: a detector could easily spot that the light waves were being flipped upside down, revealing the presence of the cloak.

But according to Zhang, the advantages of his new material are that it is immune to this effect and can also be produced using the same technique employed to manufacture microchips. This means it can be scaled relatively cheaply to cover much larger objects.

That said, the purpose-built structure masked as a proof-of-principle in the current study was roughly the size of a human hair, end-on, and the paper shows the surface working effectively only with red light at the moment although the researchers say it should be possible to make it work with the full range of visible wavelengths of light.