One of the disadvantages of invisibility cloaks is that anything placed inside one is automatically blinded, since no light can get in.
Now Yun Lai and colleagues from The Hong Kong University of Science and Technology have come up with a way round this using the remarkable idea of cloaking at a distance. This involves using a “complementary material” to hide an object outside it.
Here’s the idea: complementary materials are designed to have a permittivity and permeability that are complementary to the values in a nearby region of space. “Complementary” means that the values cancel out the effect that that this region of space has on a plane lightwave passing through. To an observer, that region of space simply vanishes.
Cloaking a region of space is relatively straightforward but cloaking an object in that space is another matter. Lai and co say the trick is to work out the optical properties of the object and then embed the “complementary image” within the cloaking material. So a plane wave would be bent by the object but then bent back into a plane as it passes through the cloaking material.
Et voila: cloaking at a distance. And in a way that doesn’t leave the cloaked object blind.
Of course , creating the complementary materials necessary to do this trick is another matter. And the usual caveats apply: it works only at a single frequency in 2D. But cloaking, in theory at least, is looking more interesting by the day.
Ref: arxiv.org/abs/0811.0458: A Complementary Media Invisibility Cloak that can Cloak Objects at a Distance Outside the Cloaking Shell