There are several projects aiming to develop something which could fool the eye as well as infrared sensors(Picture: TNO/Holst Centre).
By David Hambling, technology expert
There is a story that when the original 'Predator' movie was released in 1987, the makers were approached by the US military.
They were interested in the invisibility gear used by the alien hunter. Of course, that was all done with special effects.
Three decades later, as the latest film in the series comes out, technology is getting closer to turning Hollywood dreams into reality.
Camouflage can be extremely effective, but any given type only works against certain backgrounds. That's why armies issue different uniforms, depending on whether operations are planned in a desert or densely wooded area.
The ideal would be an adaptive camouflage which changes colour depending on the background.
In 2011, BAE Systems demonstrated 'Adaptiv', a set of hexagonal tiles covering a vehicle which alter to blend into the surroundings.
However, the device seems to have been powered off during the show, so it just looked like a helmet covered in triangular yellow tiles.
This makes it hard to assess how well the system will work in practice, in particular how it copes with high contrast and changing light.
Powered active camouflage, which relies on cameras to analyse the background and displays to copy it, will always be limited.
It would be far better to have something more like the invisibility suits in Predator.
This sort of magic always seemed as impossible as Harry Potter’s invisibility cloak, until the 1990s when British physicist John Pendry developed the theory for metamaterials, materials which can manipulate light in new ways.
Metamaterials could, in principle, bend light around an object so the light appeared to pass right through it, making the object invisible.
Building a real-life invisibility cloak is challenging though. They need to be structured on a microscopic scale, and the designs so far are for rigid shells rather than flexible cloaks.
Also, they tend to only work for a limited range of wavelengths. While there has been considerable progress with metamaterials in the microwave range, which could help aircraft disappear from radar, experts believe that practical invisibility in the visible range is still many years away.
Some developers claim otherwise. In particular Guy Cramer, CEO of Canadian camouflage makers Hyperstealth, says that in 2011 he produced a Quantum Stealth technology which completely hides an object by bending all visible light around it.
Few people believe Cramer’s claims; he keeps Quantum Stealth under wraps and has never staged a demonstration, so it remains completely unproven.
However, his company is a major player in the camouflage world, and he is in discussion with the US military.
This gives Cramer far more credibility than any small-time inventor (or hoaxer) who claims to have made an invisibility cloak in his garage.
Some even suspect that military invisibility suits are already in use.
There are plenty of rumours, and even a video of what is claimed to be such a suit in action in Iraq:
While this may be no more real than the special effects in 'The Predator', the technology is certainly coming.
It is likely to be kept secret for as long as possible though: tactical invisibility will provide a huge advantage for Special Forces and others on covert missions, especially if the opposition are not aware of it.
The only question is how long it will be before we get to see it in action.