Thin, Active Invisibility Cloak Could Shield Military Aircraft from Radar

An invisibility cloak may not just be something you find in the Harry Potter books. It turns out that two researchers have managed to demonstrate an effective invisibility cloak that is not only thin, but is also scalable and adaptive to different types and sizes of objects. The findings could open a whole new way to obscure objects in the environment.

This new invisibility "cloak" isn't exactly some sort of cape. Instead, the researchers employ small antennas that collectively radiate an electromagnetic field. This radiated field cancels out any waves scattering off the cloak object.

Picture a mailbox sitting on the street. When light hits the mailbox and bounces back into your eyes, you see the mailbox. When radio waves hit the mailbox and bounce back to your radar detector, you also detect the mailbox. So what happens when antennas radiate a field away from the box? It becomes invisible and undetectable to radar.

"We've demonstrated a different way of doing it," said George Eleftheriades, one of the researchers, in a news release. "It's very simple: instead of surrounding what you're  trying to cloak with a thick metamaterial shell, we surround it with one layer of tiny antennas, and this layer radiates back a field that cancels the reflections from the object."

So how effective is the new cloak? The demonstration effectively cloaked a metal cylinder from radio waves using one layer of loop antennas. In fact, this system can be scaled up to cloak larger objects using more loops. These loops could also become printed and flat, like a blanket or skin. This, in turn, could help design new objects that could be completely invisible to radar.

The findings have applications for hiding military vehicles and conducting surveillance operations. In addition, it could eliminate objects such as structures interrupting signals from cellular base stations. The system could also alter the signature of a cloaked object, making it appear bigger, smaller or even shifting it in space.

"There are more applications for radio than for light," said Eleftheriades in a news release. "It's just a matter of technology--you can use the same principle for light, and the corresponding antenna technology is a very hot area of research."

The findings are published in the journal Physical Review X.