Invisibility Cloaks Inch Closer to Reality

Real-world invisibility cloaks are not only theoretically possible -- they may be coming faster than anyone might have guessed, a few years back.

The cloaks would rely on so-called "metamaterials": composites structured to let electromagnetic waves flow them, rather than reflect those waves back. (That's a called "negative refractive index" in science-speak.) In theory, it should work with any wavelength -- ultraviolet, microwave, visible, you name it. But, in practice, "invisibility in the optical spectrum will be challenging because metamaterials will need to be constructed on a scale corresponding to the wavelengths of visible light, which is just a few hundred nanometers," DANGER ROOM's David Hambling noted. "That technology will not be around for at least five years."

Except now, researchers at Purdue University are saying they've created a metmaterial that bends "infrared light with a wavelength of 813?nm. This is claimed to be the shortest wavelength yet for such a metamaterial and lies just outside of the visible spectrum at
380–780?nm," according to Physics Web.

Speaking at the recent March Meeting of the American Physical Society in Denver, Vladimir Shalaev of Purdue University, unveiled a new [metamaterial]
that is tantalizingly close to the visible range. The metamaterial is a thin sheet comprising two layers of silver separated by alumina. The structure is perforated with a regular array of rectangular-shaped holes to create a "fishnet" pattern...

*Shalaev told *Physics Web that the fishnet structure could be adapted to create a [metamaterial] for visible light -- something that he and his colleagues are working on right now. However, he cautioned that fishnet NIMs display negative permeability over a relatively narrow band of wavelengths and therefore it is unlikely that a single structure could be used to create a [metamaterial]
that works throughout the visible spectrum.