From BBC News
A US-British team of scientists has successfully tested a cloak of invisibility in the laboratory.
The device mostly hid a small metal cylinder from microwaves in tests at Duke University, North Carolina.
It works by deflecting the microwaves around the object and restoring them on the other side, as if they had passed through empty space.
But making an object vanish before a person’s eyes is still the stuff of science fiction – for now.
The cloak consists of 10 fibreglass rings covered with copper elements. This is classed as a “metamaterial” – an artificial composite that can be engineered to produce a desired change in the direction of electromagnetic waves.
The precise variations in the shape of copper elements patterned on to the ring surfaces determines their properties.
In the experiment, the team used microwaves to try to detect the metal cylinder within the cloak.
Like light waves, microwaves bounce off objects making them visible and creating a shadow, though at microwave frequencies the detection has to be made by instruments rather than the naked eye.
Gone from view
The metamaterial cloak channelled the microwaves around the object like water in a river flowing around a smooth rock.
When water flows around a rock, the water recombines on the opposite side. Someone looking at the water downstream would never guess it had passed by a rock.
“This cloak guides electromagnetic waves around a central region so that any object at call can be placed in that region and will not disturb the electromagnetic fields,” said co-author Dr David Schurig from Duke University.
In principle, the same theoretical blueprint could be used to cloak objects from visible light. But this would pose a challenge, as nano-scale engineering would be needed to make the cloak.
“As an application it’s not clear that you’re going to get the invisibility that everyone thinks about – as in Harry Potter’s cloak, or the Star Trek cloaking device,” said co-author David Smith of Duke.
“But it shows what can be done with artificial materials. It gives us some insight that we can design something that we wouldn’t have been able to do with any existing material.”
A key collaborator on the project was Professor John Pendry from Imperial College London.
The researchers say that if an object can be hidden from microwaves, it can be hidden from radar – a possibility that will fascinate the military.
Cloaking differs from stealth technology, which does not make an aircraft invisible but reduces the cross-section available to radar, making it hard to track.