Here light is bent or 'refracted' as it passes from air through glass and water. The same principle might one day be used to make light pass around objects, rendering them invisible.
Credit: iStockphoto
CHICAGO: Physicists may have finally come up with a workable design for an invisibility cloak. It might one day be used to hide objects as big as aeroplanes, they say.
"It looks pretty much like fiction, I do realize, but it's completely in agreement with the laws of physics," said Vladimir Shalaev, lead researcher behind the technology.
Last year experts worked out the complex mathematical equations for making objects invisible by bending light around them.
Now, engineers led by Shalaev at Purdue University in Indiana, U.S., have used those calculations to design a relatively simple device that they predict could camouflage an object as big as an aeroplane. They reveal their design in the British journal Nature Photonics.
The design calls for tiny metal needles to be fitted into "hairbrush-shaped" cone at angles and lengths that would force light to pass around the cloak. Theoretically, this would make everything inside the cone less visible – and potentially invisible - because the light would no longer reflect off them.
"Ideally, if we make it real it would work exactly like Harry Potter's invisibility cloak," said Shalaev. "It's not going to be heavy because there's going to be very little metal in it."
Shalaev said he needs to secure funding to build the device and expects it would take two to three years to come up with a working prototype. The major limitation is that the current design can only bend the light of a single wavelength at a time, and does not work with the entire frequency range of the visible spectrum.
"How to create a design that works for all colours of visible light at the same time will be a big technical challenge, but we believe it's possible," Shalaev said. "In principal it's doable."
Even blocking a single frequency however, could lead to useful applications.
The cloak could shield soldiers from night-vision goggles, which use only one wavelength of light. It could also be used to hide objects from "laser designators" used by the military to illuminate a target, he said.
Other researchers have managed to clock objects from the microwave range of the spectrum, which are much larger than the wavelengths of visible light (see, Invisibility cloak unveiled, Cosmos Online).
But, this new design is the first for cloaking objects of any size in the range of light visible to humans. It works by using tiny needles to alter the "index of refraction" around the cone.
Every material has its own refractive index, which determines how light bends and slows down as it passes from that material into another. It's commonly described as the bent-stick-in-water effect - which occurs when a stick placed part under water looks bent when seen from outside the water.
Natural materials typically have a refractive index higher than one. But the tiny metal needles layered inside the cone would work to gradually alter the index from zero at the inner surface of the cloak, to one at the outer surface. This should guide light around the cloaked object.
The technology for making the tiny needles is already used to make nanotech devices. The needles in the theoretical design are about as wide as 10 nanometers, or billionths of a metre, and 100 or more nanometres long. A single nanometre is roughly the size of 20 hydrogen atoms strung together.
