For an object to be truly invisible, it should neither reflect (scatter) nor absorb light. Instead, it should let light "slide around [it] like water flowing around a smooth rock in a stream". Today's NYTimes reports that an object has been rendered invisible to microwave radiation:
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. [...]
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.
The Scientific American has some more details, including a picture of the 'copper cylinder' (it's actually copper etchings on fiberglass), and another showing the comparison between simulations and experimental results on how the microwave 'flows around' the cylinder.
Forget invisibility for a moment. In the NYTimes article, what is highly visible -- and very admirable too -- is the unwillingness of the Duke team's leader Prof. David Smith to hype their work to beyond what it really is about:
But Dr. 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. The chance of creating such a device is “dim,” he said, but, “The theory doesn’t prevent it from an electromagnetic point of view.”