A prototype “invisibility cloak”, similar to those worn by fictional wizard Harry Potter, has been developed by European scientists.
By Andrew Hough
Published: 9:00AM GMT 19 Mar 2010
British and German researchers have created the three-dimensional that can hide objects by bending light waves, which could pave the way for larger objects to be made invisible.
While the cloak of invisibility has played a major role in fiction and movies, it appears that scientists have taken a small, but important new step, toward making it reality.
In their study, researchers from the German Karlsruhe Institute of Technology and Imperial College London used the cloak, made using photonic crystals with a structure resembling piles of wood, to conceal a small bump on a gold surface.
In their study, published Thursday in the American journal Science, they rendered almost entirely invisible the bump that measured 0.00004 inches high by 0.00005 inches across, by “cloaking” it in a new material.
Invisibility cloaks have already been developed but they only worked on two dimensions.
In other words, the objects that were supposed to be made invisible were immediately visible from the third dimension, the study said.
The “cloak” invented by the European team is the first to work on three dimensions.
It is composed of special lenses that bend light waves to suppress light as it scattered from the tiny bump the researchers were trying to make disappear, the study says.
“For now these … cloaking devices are just a beautiful and exciting benchmark to show what transformation optics can do,” said Tolga Ergin, who led the research.
“This is very exciting, because mankind has always thought about being invisible or having invisibility cloaks.
“This is the first proof of principle. It shows that the technique works.
He added: “The value of the finding is that we learn more about the concepts of transformation optics, and that we have made a first step in producing 3-D structures in that field.”
He cautioned that it likely be years before anything as large as a person, car or tank could be made to disappear with this technique.
“There have been proposals in the field of transformation optics for different devices like beam concentrators, beam shifters, super antennas which concentrate light into one point from all directions, and much, much more,” he said.
“It is really hard to say what the future will bring, but the field is definitely very broad and the possibilities are very large.”
Cloaking device makes objects invisible – to infrared light anyway
For now the device only makes objects invisible to infrared light, but it paves the way for a cloaking material that could hide vehicles, high-security facilities or unsightly buildings.
Ian Sample, science correspondent
guardian.co.uk, Thursday 18 March 2010 18.02 GMT
Scientists are a step closer to creating a Star Trek-style cloaking device after demonstrating a material that makes objects beneath it appear to vanish.
The material was used to hide a bump on a surface by interfering with the way light bounced off it, making it seem as though neither the cloak nor the bump was there.
The cloak was designed to make objects invisible to infrared light, but the work paves the way for more advanced materials capable of cloaking objects in visible wavelengths.
Some scientists believe cloaking materials could be used to hide unsightly buildings or high-security facilities, and even make vehicles seem to disappear from view.
Tolga Ergin and Nicolas Stenger at the Karlsruhe Institute of Technology in Germany used a technique called direct laser writing lithography to create a sheet of cloaking material from tiny plastic rods. The spacing of the rods, each of which measured one thousandth of a millimetre wide, alters a property of the material known as the refractive index, which changes the speed of light inside it.
The researchers placed a piece of the material over a dimple in a gold sheet and used infrared cameras to see what happened. When the cloak was in place, it altered the speed of light around the bump in such a way that the gold sheet appeared to be flat. The experiment was equivalent to hiding something under a carpet and having the carpet disappear too.
It is the first time researchers have demonstrated a cloak that works in three dimensions. Previous devices have hidden objects when looked at head-on, but did not work if viewed from the side. “We were surprised that the cloaking effect was still so good, Ergin told the US journal, Science.
Inside the material, the plastic rods are arranged like planks of wood piled up on each other. The high precision of the structure means it is possible to control the refractive index so it varies in just the right way to bend light around whatever object is hidden beneath it.
“The material has a higher refractive index on top of the bump, so light hitting that part is slowed down a little bit compared with light impinging on the rest of the surface,” said Stenger. “That compensates for the shape of the bump, and in the end, it is exactly as if there was no bump.”
Research into cloaking devices has attracted funding from military organisations, such as the US Defence Advanced Research Projects Agency, which backs high-risk science research for the Pentagon. In the near term, cloaking materials are expected to be used to hide aircraft from radar more effectively.
As yet, scientists have not been able to develop cloaking materials that make objects invisible to the eye, because visible light has shorter wavelengths that are more difficult to manipulate in the right way.
Beyond military applications, cloaking devices are drawing interest from telecommunications companies, who see them as a way to send information by light more efficiently. One idea is to use the new materials to build “superantennas” that can concentrate light and other electromagnetic waves to make laser-like beams.
“We are focusing on a new way to control light,” said Stenger. “In the future of technology, light is going to have more and more importance.”
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