Real-Life Invisibility Cloak Is Science, Not Magic; New Design Nearly Makes Objects Vanish
In Harry Potter, the characters accomplish various feats of espionage using a cloak that renders the wearer completely invisible. Fans say it was probably made from the hair of a magical invisible ape.
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Meanwhile, in the world of nonfiction, scientists have been trying to perfect an actual invisibility cloak, one that seems to pluck the colors from the world around it and completely vanish from view. Two researchers in Texas say they're getting closer.
Until last month — when Andrea Alù and Francesco Monticone, of the University of Texas at Austin, published an article on their research — invisibility cloak technology wasn't all that great. It consisted of various materials called metamaterials, textiles made up of microscopic geometric designs, that can bend the light around an object and effectively cause it to vanish. The problem is, those metamaterials could only be tuned to a specific electromagnetic frequency, such as red, for instance.
As Alù and Monticone conclude in their article, published in the journal Physical Review X, the result can actually make the objects more obvious, not less. "For example, you might make a cloak that makes an object invisible to red light. But if you were illuminated by white light (containing all colors) you would actually look bright blue, and therefore stand out more," Alù told the BBC.
He described these materials as "passive" and has said it's "impossible" to achieve true invisibility using these current designs. The result of the study came to focus on a new kind of design, an "active" metamaterial, that can manipulate the entire visible spectrum using electrically charged surfaces.
"If you want to make an object transparent at all angles and over broad bandwidths, this is a good solution," Alù said. "We are looking into realising this technology at the moment, but we are still at the early stages."
Researchers from the University of Toronto seem to be on the same track as the ones in Texas, according to a new study announced Tuesday. In a paper also published in Physical Review X, George Eleftheriades and doctoral student Michael Selvanayagam demonstrated how they could beam the visible waves around an object using thousands of tiny antennas on a thin, flexible material. It radiates light or radio waves away from whatever it is they cover.
In their demonstration, they used a single loop of antennas to make a metal cylinder invisible to radio waves. But the scientists say they can scale it and adapt it to something like a blanket.
"We've demonstrated a different way of doing it," Eleftheriades said in a statement. "It's very simple: Instead of surrounding what you're trying to cloak with a thick metamaterial shell, we surround it with one layer of tiny antennas, and this layer radiates back a field that cancels the reflections from the object."
The first invisibility cloak was tested in 2006, but it was hardly what most people would think of as an "invisibility cloak." It deflected microwaves around a piece of copper. David Smith, a Duke University scientist who developed that 2006 cloak, says the possibilities of "active" invisibility cloaks are exciting.
"So, this finding does not necessarily preclude the Harry Potter cloak, nor does it preclude any other narrow bandwidth application of cloaking."
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