Experts create invisibility cloak

By Paul Rincon
Science reporter, BBC News



The cloak is constructed from advanced "metamaterials"

A US-British team of scientists has successfully tested a cloak of invisibility in the laboratory.

The device mostly hid a small copper 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.


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.


The metamaterial cloak channelled the microwaves around the object like water in a river flowing around a smooth rock. The frequency range of the microwaves was about 8GHz - in the same range as radar.


Gone from view

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 an obstacle.


In the experiment, the scientists first measured microwaves travelling across a plane of view with no obstacles. Then they placed a copper cylinder in the same plane and measured the disturbance, or scattering, in the microwaves.


Scientists were able to watch waves bending around the cloak

Finally, the researchers placed the invisibility cloak over the copper cylinder. The cloak did not completely iron out the disturbance, but it greatly reduced the microwaves being blocked or deflected.


"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," explained co-author Dr David Schurig from Duke University.


"There is reduced reflection from the object, and there is also reduced shadow."


In principle, the same theoretical blueprint could be used to cloak objects from visible light. But this would require much more intricate and tiny metamaterial structures, which scientists have yet to devise.


"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.


Professor John Pendry, of Imperial College London, who was an author on the paper, said: "There's a rule about the internal structure of the metamaterial: it has to be smaller than the wavelength of radiation. So for radar waves that's 3cm. You can easily engineer something a few millimetres across.


"You go up to optical radiation - light - and the wavelength is less than a micron. So your microstructure has to be a few tens of nanometres across. and we're only just learning how to do nanotechnology. It's some way off if ever.


"Maybe in five or 10 years time you could do this, but not today."
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.

Hmmm, I wonder about weight concers as this pertains to airborne use. You get enough copper in one spot, and its darn heavy (just over twice as heavy as Aluminum, only about 20% heavier than Titanium but with no where near the strenthg of either, I believe) and its very subsceptible to the elements.