Researchers have demonstrated an invisibility cloak that can be scaled to almost any size and say it could be used to hide orbiting satellites.
John Howell at the University of Rochester in New York, and Benjamin Howell, show how to make simple cloaks that hide huge objects over the entire optical spectrum, albeit with a significant compromise. One of their devices is big enough to cloak a person.
Their approach is head-slappingly simple. Instead of using complex metamaterials to steer light, the Howells do the same job with conventional lenses and mirrors.
The mirror cloak is not actually a new design and has been used for years by magicians, a point the Howells readily acknowledge. “The point we wish to emphasize is not the novelty but the ease of scaling to nearly arbitrary size,” they say.
These cloaks aren’t perfect by any means. In fact there is one very significant caveat in their design—they only work in one direction. View these cloaks from anything other than this direction and the ruse is quickly revealed.
They demonstrate three simple cloaking devices that can hide very large spatial objects over the entire visible spectrum using only passive, off-the-shelf optics. The cloaked region for all of the devices exceeds 10^6 mm3 with the largest exceeding 10^8 mm3. Although uni-directional, these cloaks can hide the cloaked object, even if the object is transversely or self-illuminated. Owing to the small usable solid angle, but simple scaling, these cloaks may be of value in hiding small field-of-view objects such as mid- to high-earth orbit satellites.
In summary, we have demonstrated three straightforward optical cloaking devices. The cloaks work over the visible spectrum, have cloaking regions exceeding 10^6 mm3 and with good coatings, the second device can be made nearly invisible. The second device does not suff er from edge e ffects for straight-on viewing. The downside is that all of these devices are only uni-directional. The devices may have value, for example, in cloaking satellites in mid- to high-earth orbit or for any low field-of-view cloaking. It should be pointed out that transverse-or self-illumination of the cloaked object still renders the object invisible to the observer. While it has been shown that perfect invisibility cannot be attained, an open question is if standard optics can achieve geometric (ray optic) omni- or multi-directional cloaking. The authors believe that a cloak with spherical symmetry (much like retro-reflecting spheres achieve multi-directional reflection may achieve this end.