- Lurking in the shadows (Image: Thomas Dworzak/Magnum Photos)
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The US army wants invisibility cloaks for its soldiers. Not just that – it has announced that it wants to test the best contenders within the next 18 months. Seems a bit unrealistic? Well, we may not be as far away as you think.
In 2006, John Pendry, a theoretical physicist at Imperial College London, showed that it should be possible to bend light around an object and hide it using metamaterials – structures engineered at microscopic levels to channel electromagnetic waves. Since then, many devices trumpeted as invisibility cloaks have been described, but they only work in the lab with specific wavelengths or from certain angles.
Now the US army has made a call for proposals from companies for wearable camouflage with a chameleon-like ability to change according to the background. So how will they manage this? Metamaterials are probably the best solution: previous efforts in this field using technology like LEDs were hampered by power and computing requirements.
But although they can bend light, metamaterials cannot make things disappear completely.
"Complete invisibility of macroscopic objects for all visible colours is fundamentally impossible," says Martin Wegener of the Karlsruhe Institute of Technology in Germany. His team has created cloaks from photonic crystals that work for certain wavelengths, but bending light over the entire spectrum is forbidden by relativity.
"This means that you may see less of something at a particular colour, but see it at all other colours," says Wegener.
The wearer would be effectively transparent at some wavelengths but not all, rendering them as a coloured shadow or ghost image.
Contractors will demonstrate the feasibility of their approach in the first six months of the programme. Those selected for the following one-year phase will submit 10 prototype uniforms for testing. These need to work in all terrain from all angles. They also need to function across a wide range of temperatures, in rain and snow, and without hampering a soldier's normal duties.
If the adaptive camouflage requires a power source, this must weigh no more than 0.45 kilograms and provide at least 8 hours of operation.
Some firms claim to be on their way there already. Guy Cramer, CEO of Canadian camouflage makers Hyperstealth Biotechnology, says he demonstrated metamaterial camouflage to US military scientists last year, and that the new project will allow him to move forward with it. But Cramer won't yet reveal details or release photographs of the material.
Metamaterials might be used to generate adaptive camouflage patterns rather than for cloaking, suggests Andrea di Falco of the University of St Andrews, UK.
The new specimens will be compared with existing camouflage patterns using standard NATO tests, indicating that something less than complete invisibility is expected.
However, as Wegener points out, the word "invisible" can mean different things. If the wearer looks like a shadow among other shadows and cannot be identified as a person, they may be invisible enough for military purposes.
This article appeared in print under the headline "The invisible soldier"