New Radio Cloaking System Makes Objects Undetectable by Radar

By surrounding an object with small antennas that collectively radiate an electromagnetic flied, a team of researchers have developed a functional invisibility cloak that is thin, scalable and adaptive to different types of objects.

The system does not make its user invisible to the naked eye, but by covering an object in tiny antennas that cancel out radio waves bouncing off the object, the system creates a field around the object that is invisible to radar.

Beyond obvious useful applications in the military, such as hiding vehicles from radar, the researchers say the technology could also be used to eliminate obstacles. Structures that interfere with signals from cellular base stations, for example, could be cloaked by the antenna system, allowing signals to pass freely.

"We've taken an electrical engineering approach, but that's what we are excited about," said George Eleftheriades, a professor at the Edward S. Rogers Sr. Department of Electrical & Computer Engineering at Universty of Toronto. "It's very practical."

Eleftheriades and his colleague Michael Selvanayagam, a University of Toronto PhD student, published a record of their work in the journal Physical Review X.

When you look at something, your eyes are seeing a reflection of light bouncing off the object you're looking at. Radar functions under a similar principle. Radio waves bounce off objects in their path. If radio waves bounce off a tank, for example, a tank is detected by the radar operator.

The system developed by the engineers tricks radar into passing by an object it would normally pick up. According to the researchers, if that tank were shrouded in one layer of these tiny antennas, a signal radiating away from it would be projected and would cancel out any waves that would bounce back to a radar detector, rendering the object undetectable.

Making something invisible has been a science fiction fantasy that, over the years, has become more grounded in reality. Engineers from various institutions have been developing their own versions of invisibility systems for years. 

"We've demonstrated a different way of doing it," Eleftheriades said. "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."

For their proof-of-concept experiment, the researchers cloaked a metal cylinder from radio waves with one layer of tiny loop antenna. Eleftheriades said the system could be scaled-up to cloak larger objects and that the loop antenna could eventually be printed flat like a blanket. Currently, the loop antenna must be tuned manually to the electromagnetic frequency they need to cancel, but in the future, the researchers said the tuning process could automatically adjust to the waves they need to cancel out in real time, much like the technology behind noise-canceling headphones.

While the current system only works on radio waves, Eleftheriades said as the antenna technology improves in the future, the concept could be re-tuned and applied to Terahertz (T-rays) or light waves.

"There are more applications for radio than for light," Eleftheriades said. "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."