Invisibility-Cloak Breakthrough

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Even for physicists and engineers, the math involved in the theoretical design of cloaking devices is very difficult, says Nicholas Fang, a professor of mechanical science and engineering at the University of Illinois at Urbana-Champaign. The way that a material interacts with light's magnetic and electric components is taken into account in determining the size, shape, and orientation of each structure in a metamaterial. Pendry and Li's theoretical work described how to make a broadband cloak by using materials structured so that they have an electrical response to light, but not a magnetic one. But it wasn't clear how to put this idea into practice. The Southeast University researchers developed new algorithms to greatly speed up the process, says Smith. These algorithms make it possible to quickly predict how a structure with a particular shape will interact with light.

The cloak itself, described this week in Science, is indeed impressive, says Fang, who's working on metamaterials for super-resolution biological imaging. But what's more exciting is that the new approach to design will accelerate the development of other metamaterials. Smith says that he and his group have already moved beyond the cloak reported in Science, but because their latest work is unpublished, he can't specify what they've made. "Now [that] this is becoming a more feasible technology," he says, "we will start to see a lot more of it."

Other applications of metamaterials, says Smith, include optical devices that take light energy and concentrate it, instead of turning it away--conceptually, the opposite of a cloak. "You could improve solar cells by making structures to increase the field strength of the light," he says. The new work suggests that this could be done over the whole spectrum of wavelengths found in sunlight. Similarly, broadband "hyperlenses" that gather up light missed by normal lenses could revolutionize biological imaging. Fang and others have developed narrowband hyperlenses with resolutions of only a few nanometers, which make the molecular workings of cells visible. A broadband hyperlens could work with all colors of visible and infrared light.

The ultimate goal, says Pendry, is cloaking in the visible-light spectrum, and Smith's latest work points the way forward. "There are no insuperable obstacles to making a cloak work at optical frequencies," Pendry says. "The Duke paper brings this goal a step closer."