From KurzweilAI.net, taking steps toward an invisibility cloak …
New material may be step towards 3D invisibility cloak New Scientist, May 13, 2008
A researcher at the University of California at Berkeley claims to have made a 3D metamaterial with a negative refractive index, the first 3D material of this kind.
Physicists have in recent years made it possible to bend, or refract, light in the opposite direction to any natural materials. These metamaterials make it possible to create invisibility cloaks that hide an object by steering light around it. The materials and “invisibility cloaks” built so far have all been flat, working only in two dimensions.
The negative refraction index will have to be confirmed by measuring the speed of light in the material.