Invisibility Cloak Demonstrated

Invisibility has long been the stuff of fantasy, from Plato's story of the ring of Gyges to Harry Potter's mischief-enabling cloak. But scientists led by a team at Duke University have demonstrated a technology that could be a small step in the right misdirection.

Recently published theory has suggested that a cloak of invisibility is in principle possible, at least over a narrow frequency band. Within five months of the publication of such a theory the first practical realization of such a cloak has been made. Department of Electrical and Computer Engineering, Duke University and others have made a demonstration of the principle of invisibility, a copper cylinder is 'hidden' inside a cloak constructed according to the previous theoretical prescription. The cloak is constructed using artificially structured metamaterials, designed for operation over a band of microwave frequencies. The cloak decreases scattering from the hidden object whilst at the same time reducing its shadow, so that the cloak and object combined begin to resemble free space.

The system, a set of concentric copper circles on fiberglass board, deflects electromagnetic waves of a specific frequency that strike it, without much of the scattering and absorption that make reflections and shadows.
A result is that the microwaves slide around the structure like water flowing around a smooth rock in a stream, said David Smith, a professor of electrical and computer engineering at Duke and an author of the paper published today 20/10/2006 in the journal Science.

The exact structure of the circles was described in an earlier paper by Sir John Pendry of Imperial College in London, who worked with the Duke group to see his theory etched into a working model by means of the process used to print circuit boards. In the recent paper, researchers said they had successfully cloaked a copper cylinder.

Enthusiasts have already suggested that the technology may someday be useful for the military to create objects that are invisible to radar or to shield equipment from cellphone signals. But Smith warned against getting ahead of the day's announcement and envisioning the disappearing Romulan warbirds of "Star Trek" on the horizon. The work "is really a scientific explanation," he said, adding, "Whether it's useful is always a question." Creating a cloaking device in the visible spectrum would be vastly more complex, he said, since the device would have to warp all of the wavelengths of light.

Objects are visible because light bounces off them; if this can be prevented and if the objects did not reflect any light, they would become invisible. A "plasmonic screen" could achieve this by resonating in tune with the illuminating light. "Plasmons" are created when the electrons on the surface of a metallic material move in rhythm. The developers claim a shell of this material will reduce light-scatter to the extent that an object will become invisible, if the light’s frequency is close to the resonant frequency of these "plasmons". In this way, the scattering from the shell effectively cancels out the scattering from the object.

Businesses are already looking at possible applications, said Nathan Myhrvold, a former chief technology officer of the Microsoft Corporation whose company, Intellectual Ventures, explores the potential of new inventions. "We hope it's got some commercial potential," Myhrvold said. "It could easily take years to figure out what the stuff is really good for from a practical, pragmatic standpoint. But, boy, it sure is really cool from a short-term standpoint."