First 'invisibility cloak' appears
26 October 2006
Ever wished you could be invisible? Scientists have just taken the first step towards making this fantasy a reality. They've conjured up the world's first 'invisibility cloak'. So far, it only hides objects from microwaves, but there could be more to come. Antenna investigates...
Scientists have recently unveiled their 'invisibility cloak'.
Image: Duke University
The 'cloak' isn't a piece of clothing - it's made from circular bands of fibreglass packed with copper wire loops. Its creators say it's one of the most sophisticated materials ever made - a metamaterial. And this is the secret of its hidden talents.
'The response of ordinary materials to light, and other electromagnetic waves such as microwaves, depends on the properties of the atoms and molecules they are made of. Metamaterials are different - their unusual responses are due to their physical shape and structure.'John Pendry, invisibility expert, Imperial College
John Pendry, invisibility expert, Imperial College
Image: Imperial College
How does the invisibility cloak work?
Waves of radiation normally bounce off solid objects in different directions, but the metamaterial stops this happening. The microwaves are guided smoothly around its surface, largely returning to their original pattern on the other side as if the object isn't there.
Watch the microwaves move around the cloak, returning almost to normal on the right-hand side.
Video: Duke University
'We demonstrated complete control over electromagnetic waves so that we can even make them flow around obstacles like water.'John Pendry
The current cloak works in just two dimensions, so a big step on the horizon is to make a three-dimensional version. 'But first, we want to improve the design of our metamaterials to make an even more perfect cloak,' says John Pendry.
In the future, the cloak could be used to shield top-secret military kit from the prying eyes of radar beams. Metamaterials could also control mobile phone radiation, or even improve magnetic resonance imaging (MRI) in hospitals.
Stealth aircraft like this American B2 plane are difficult to detect because of their design and the special materials they are made from, but even these hi-tech flying machines are not invisible.
Image: Cecilio Ricardo
In theory, metamaterials could be made invisible to all kinds of electromagnetic radiation - microwaves, X-rays, visible light and radio waves.
'We could apply the technique to seismic or sound waves, creating shields from those disturbances as well. You could potentially earthquake-proof a building or create a quiet concert hall even next to a motorway.
'Because these cloaks isolate their contents, they can create a shielded quiet zone, which could protect people or sensitive equipment, like a pacemaker.'David Schurig, invisibility expert, Duke University, USA
David Schurig, invisibility expert, Duke University, USA
Image: Duke University
But in practice, some types of invisibility will be easier to achieve...
Electromagnetic radiation travels in waves which vary in length. To be invisible, the structure of the metamaterial has to be smaller than the radiation wavelength that's hitting it.
The internal structure of the cloak is made up of loops and coils of copper wire set a few millimetres apart.
Image: Duke University
'Microwaves typically have a wavelength of a few centimetres, visible light less than a thousandth of a millimetre. It is much easier to manufacture metamaterials for use with microwaves, because they are bigger!'John Pendry
Making things invisible to human eyes won't be easy. We use white light, such as sunshine, to see and this is made up of tiny wavelengths from all across the colour spectrum. So to make things disappear we'd need a metamaterial made using individual atoms.
Image: Stock.XCHNG