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Scientists set sights on invisibility cloaks

  • Story Highlights
  • Models used to show how a superlens could make small objects seem to disappear
  • Team's simulations work in theory but have not been experimentally confirmed
  • Another group of scientists has made a device that can cloak microwaves
  • Device also could be used to minimize interference in cell phone reception
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By Elizabeth Landau
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(CNN) -- Wouldn't it be great if you could become invisible whenever you wanted? Harry Potter can do it, and so could certain groups of futuristic creatures on "Star Trek."

This device, developed at Duke University, can make microwaves invisible but not visible light.

Graeme Milton and colleagues have come up with a theory for how small objects could become invisible.

Such technology remains far off, but it may not be entirely impossible.

Teams of scientists around the globe say they're making progress on theories and experiments involving cloaking -- that is, making things invisible.

In theory, all that's needed to make a small object invisible is something called a superlens, says Graeme Milton, a mathematician at the University of Utah.

He and Australia-based collaborators Nicolae Nicorovici, Lindsay Botten and Ross McPhedran have made mathematical models showing that at a critical distance from a superlens, an object would seem to disappear.

A superlens has a negative refractive index, meaning light that hits it reverses and goes in the opposite direction. Physicist John Pendry at Imperial College London was among the first to propose superlenses in 2000.

At a certain distance from a superlens, an object becomes invisible because light that bounces off it cancels out with light reflecting off the superlens, Milton said. It's a little like noise cancellation devices such as earphones, he said.

"We've seen it numerically -- not in practice, but we've got a theoretical proof that collections of particles become invisible," he said. Video Watch particles become invisible in a simulation by Milton and his collaborators »

At this stage, Milton said he wouldn't go as far as to promise that this kind of invisibility cloak would work for a large object such as a truck, but small things such as clusters of dust particles would be good candidates.

Princeton University physics professor David Huse said he is "sure this is legitimate science, although as always one needs to be skeptical of the extrapolations beyond what has already been proven."

Huse, who attended graduate school at Cornell University with Milton, said he could believe the lens could hide the object, such as an opaque screen, but he asks if the lens would be visible, too.

In mathematical models, Milton said, a superlens can correspond to space folded back on itself, meaning it too appears to be invisible. In real life, very thin gold or silver might approximate the effect, he said.

Experimentalists also are progressing in cloaking research, notably using artificially structured materials called metamaterials.

David Smith and collaborators have so far succeeded in making some light invisible -- but only microwaves, which are invisible to human eyes. Smith, professor of electrical and computer engineering at Duke University, and his team built a device with metamaterials that renders 3-centimeter (1.2-inch) lightwaves invisible.

This cylindrical device is made of material that makes the lightwaves go around the structure and get restored on the other side.

Humans can't see the difference with the device because we don't detect microwaves that are much longer than those of visible light. But if humans did have microwave vision, any object inside the device would appear as a dark spot.

Still, the object wouldn't completely appear invisible. Even microwave-sensitive eyes would see the object with some reflection, distortion and shadowing. Although this flaw has been the case for more than a year, Smith and his team are working on a much more complicated design as the next step to improve this research.

The copper patterns in the microwave cloaking device are like tiny electrical circuits, much smaller than the wavelength of a lightwave, Smith said. The circuits mimic the electromagnetic response of atoms or molecules in a material, behaving in a way that wouldn't ordinarily be found in nature.

While visible light may be far off, the research also has implications for sound. Smith's group has shown that, at least in theory, a device similar to the copper cylinder for microwaves can block sound.

In communications, a device could be used to cloak antennas from one another if they interfere with each other, Smith said. An obstruction in cell phone reception also could be cloaked, allowing signals to get through.

"You could take this technology and, even with these limitations, [it] could still be useful," he said.

As for making an army truck invisible with these techniques, Smith appears more optimistic than Milton.


"In principle, the answer is yes, but we just don't know how to do it yet," Smith said.

Besides the cloaking models, Milton is working on a different project, "something similar to a force shield in 'Star Trek,' " he said.

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