Invisibility cloaks are cool, but an invisibility carpet is more practical. That's according to scientists from Imperial College London, who recently published a paper detailing the creation of a material that would be the first to hide objects in visible light, something no cloaking device has ever achieved. "We've given a prescription for how to cloak something in visible light," said John Pendry, who, along with Jensen Li, wrote the paper that appeared recently on ArXiv.org. "It will be difficult to make but it is also practical." Cloaking an object requires structures, often referred to as metamaterials, that channel light in a specific way.The only way to channel light in that fashion is by using structures smaller than the wavelength of light being used to detect an object. In 2006, Duke University scientists cloaked an object from light centimeters long by creating a metamaterial with structures millimeters in size.
To cloak an object in visible light, which has a much smaller wavelength, around half a micron, scientists would have to create structures nanometers in size, which, according to Pendry, "requires some clever nanotechnology." That nanotechnology would come from combining special layers of common silica and silicon, each of which reflects light differently. "It's a lot like a mirage," said Pendry. "The sun heats the air above the desert and creates a temperature gradient, so when light from the sky comes down the graded refraction bends the light and it enters your eye and you see a mirage the looks like water."
Instead of creating a temperature gradient that only partially reflects light, the silicon and silica mix would create a physical gradient that instead makes light do a complete U turn, exiting in the same direction it entered. The result would look like a mirror. If you looked at it you would see your reflection. The difference is that this mirror would let you check your reflection from any angle, not just one. "This new cloak is not perfect," said Vladimir Shalaev, a professor at Purdue University in Indiana involved in metamaterial research who did not contribute to the ArXiv.org paper. "Instead it leaves an observer with illusion that there is only a flat mirror on the ground with some transparent dielectric box on top of it, whereas, in reality, there an object concealed in the "transparent" box which is not visible for the observer."
Perfect or not, it's still an important result according to Shalaev. "This 'invisibility carpet' can be fabricated and it's indeed an important step toward making the dream of invisibility true." Theory and actual fabrication are far apart, however. Pendry estimates that with appropriate funding and expertise, invisibility carpets could be produced in one to two years. "We are theorists; we have an easy life," said Pendry. "The difficult stuff is to actually make this." Source: Discovery.
To cloak an object in visible light, which has a much smaller wavelength, around half a micron, scientists would have to create structures nanometers in size, which, according to Pendry, "requires some clever nanotechnology." That nanotechnology would come from combining special layers of common silica and silicon, each of which reflects light differently. "It's a lot like a mirage," said Pendry. "The sun heats the air above the desert and creates a temperature gradient, so when light from the sky comes down the graded refraction bends the light and it enters your eye and you see a mirage the looks like water."
Instead of creating a temperature gradient that only partially reflects light, the silicon and silica mix would create a physical gradient that instead makes light do a complete U turn, exiting in the same direction it entered. The result would look like a mirror. If you looked at it you would see your reflection. The difference is that this mirror would let you check your reflection from any angle, not just one. "This new cloak is not perfect," said Vladimir Shalaev, a professor at Purdue University in Indiana involved in metamaterial research who did not contribute to the ArXiv.org paper. "Instead it leaves an observer with illusion that there is only a flat mirror on the ground with some transparent dielectric box on top of it, whereas, in reality, there an object concealed in the "transparent" box which is not visible for the observer."
Perfect or not, it's still an important result according to Shalaev. "This 'invisibility carpet' can be fabricated and it's indeed an important step toward making the dream of invisibility true." Theory and actual fabrication are far apart, however. Pendry estimates that with appropriate funding and expertise, invisibility carpets could be produced in one to two years. "We are theorists; we have an easy life," said Pendry. "The difficult stuff is to actually make this." Source: Discovery.
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