By Mark Brown
Researchers from the University of Dallas in Texas have hijacked one of nature’s most intriguing phenomena — the mirage — to make an invisibility cloak. It can hide objects from view, works best underwater and even has a near-instant on/off switch.
To understand how it works, you need to first grasp the basics of the mirage effect. This unusual experience, sometimes seen in the desert or on hot roads during the summer, can trick your brain into seeing objects that aren’t really there.
It happens when a big change in temperature over a small distance bends light rays so they’re sent towards the eye rather than bouncing off the surface. So if you see a pool of blue water in the middle of the desert it’s just the blue sky being redirected from the warm ground and sent directly into your eye. Your brain, being the clever little computer that it is, swaps this mad image out for something more sensible: a pool of water.
With that in mind, the researchers wanted to find a material that has an exceptional ability to conduct heat and quickly transfer it to surrounding areas to mimic the light-distorting temperature gradients of the desert. That material, they found, was sheets of carbon nanotubes.
The nanotubes — one-molecule-thick sheets of carbon wrapped up into cylindrical tube — have the density of air but the strength of steel. They’re also excellent conductors, making them an ideal material to exploit the “mirage effect.”
Through electrical stimulation, the transparent sheet of highly aligned nanotubes can be quickly heated to high temperatures. By transferring that heat to its surrounding areas, a steep temperature gradient is generated, which causes the light rays to bend away from the object concealed behind the device. Therefore, the object appears invisible.
“It is remarkable to see this cloaking device demonstrated in real life and on a workable scale,” said a spokesperson for the Institute of Physics. “The array of applications that could arise from this device, besides cloaking, is a testament to the excellent work of the authors.”
