U of T researchers demonstrate thin, active 'invisibility cloak'

Researchers from the University of Toronto have successfully demonstrated an "invisibility cloak" that can make objects undetectable to radar.

Prof. George Eleftheriades and PhD candidate Michael Selvanayagam have designed a new way to cloak an object by surrounding it with small antennas that radiate an electromagnetic field, effectively making it "disappear" from microwave and radio wave detectors.

A paper describing their cloaking method was published Tuesday in the journal Physical Review X.

In it, the two researchers describe attaching a layer of loop antennas to a metal cylinder. The antennas collectively radiate an electromagnetic field which cancels out any waves scattering off the cylinder.

While various attempts to create a functioning invisibility cloak have been underway since 2006, Eleftheriades believes their system has a number of advantages over past attempts.

He told CTVNews.ca that past attempts have required large, very thick material comparable to the size of the object to cover it -- a major disadvantage.

"In our approach, we don't do that. We just use a thin layer of tiny antennas," Eleftheriades said, adding that their method does not require any "scaling up" of the cloaking material as the object increases in size.

"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," he said in a statement released Tuesday.

And while the new system only shields the item from radar, the antennas could eventually be developed to render the object invisible to the human eye, Eleftheriades said.

To adapt their technology to make objects invisible to the human eye, scientists would need to develop tiny antennas that are just tens of hundreds of nanometres in size.

"This is a very active area of research," Eleftheriades said. "Once this technology matures, the same principle can be used to cloak objects to visible light."

In their statement, the researchers describe their process using an example of a mailbox on the street.

"When light hits the mailbox and bounces back into your eye, you see the mailbox. When radio waves hit the mailbox and bounce back to your radar detector, you detect the mailbox," the statement said.

The new system "wraps the mailbox in a layer of tiny antennas that radiate a field away from the box, cancelling out any waves that would bounce back. In this way, the mailbox becomes undetectable to radar."

Up next, the research team wants to make the technology fully-adaptive so it can respond and adjust in real-time to incoming broadband signals, much like noise-cancelling headphones, Eleftheriades said.

He said there are many applications for their new system, the "most obvious" being the military, where radar is used to detect "everything."

But there are other potential civilian applications for this technology, he added, including helping to make cellular reception stronger by making structures that are in the way "disappear."

"We really think this is the most practical way of doing cloaking," he said. "We're really excited."