Is a perfect invisible cloak theoretically possible? Are there certain wavelengths—such as those in the visible spectrum—that can’t be made invisible? How will using imperfect materials affect the performance of a cloak? Scientists from Zhejiang University and MIT have recently analyzed the physics behind invisibility cloaks in an attempt to answer some of these questions. Hongsheng Chen, Bae-Ian Wu, Baile Zhang, and Jin Au Kong have published their research on invisibility cloaks in a recent issue of Physical Review Letters. The group analytically demonstrated how electromagnetic waves interact with invisibility cloaks made of metamaterials, an interaction that is often different from conventional scattering with regular particles. Their findings will hopefully be useful for cloak design and applications, an exciting research area that is still in its early stages. “When an electromagnetic wave is incident onto a conventional sphere, part of the radiation will be scattered in all directions; while for a metamaterial cloak, the incident wave will smoothly pass through the cloak undeflected,” Chen explained to PhysOrg.com.

“It is very interesting that a perfect metamaterial cloak shows no reflection or absorption but rather allows the Poynting power to bypass the hidden object. Our research also shows that the Poynting power inside of the cloak is not uniform: when close to the inner boundary of the cloak, the power flow density is close to zero, while near the outer boundary of the cloak, the power flow density becomes large.”

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This sounds very much like the prismatic invisibility armor used by the fictional Predators! It makes them invisible by bending light around them. But at the point of the event horizon there's a slight visual distortion which gives them away.

This is IMO a very accurate description of how a "clocking device" would work. Apparent transparency, not invisibility, is the key. If it were invisible (no light being reflected) it would be black.

There are semi-functional working models. I've seen a demo of an invisibility material that bends light perfectly from a perfect 90 degree angle view point. But as you break from that perfect perpendicular it loses functionality.

I believe they were looking at it as a military semi-stealth for ground vehicles. Place it in front of say, a tank and at a distance you'd have a fairly wide angle of use.