The cloaking device, famously used by the Romulans in Star Trek to hide their spacecraft from enemies, may yet become reality, thanks to US researchers.

University of Pennsylvania PhD student Andrea Alu and professor Nader Engheta have written a paper for the journal Nature describing how a crude cloaking device could be built.

Mr Alu and Professor Engheta say their “plasmonic cover” could render objects “nearly invisible to an observer”.

So far, research into invisibility has concentrated on camouflage: a screen is coloured to match its background, for example. But the invisibility shield proposed by the two researchers is more ambitious – a “self-contained structure that would reduce visibility from all viewing angles”, according to Nature.

“We see objects because light bounces off them; if this scattering of light could be prevented (and if the objects didn’t absorb any light) they would become invisible. [The] plasmonic screen suppresses scattering by resonating in tune with the [frequency of the] illuminating light,” they say.

Plasmons are waves of electron density, caused when the electrons on the surface of a metallic material move in rhythm. For visible light, such plasmonic materials include silver and gold.

However, there are a couple of catches. The first is that a shield only works for one specific wavelength of light. An object might be made invisible in red light, for example, but not multiwavelength daylight.

The second catch is the effect only works when the wavelength of the light scattered is roughly the same size as the object.

So shielding from visible light is only possible for microscopic objects, not people or spaceships.

The calculations show that spherical or cylindrical objects coated with the shields scatter little light. “When lit by light of the right wavelength, the objects become extremely small, so small they cannot be seen,” according to Nature.

More here.