Researchers design new thin, adaptive 'invisibility cloak'

Source:Xinhua Published: 2013-11-13 9:47:21

An effective "invisibility cloak" that is thin, scalable and adaptive to different types and sizes of objects has been devised, a study in the US journal Physical Review X said Tuesday.

Researchers from the University of Toronto tested a new approach to make an object "vanish" by surrounding it with small antennas that collectively radiate an electromagnetic field. The radiated field cancels out any waves scattering off the cloaked object, and in this way, the object becomes undetectable to radar.

"We've taken an electrical engineering approach, but that's what we are excited about," George Eleftheriades, a professor at the university and the study's lead author, said in a statement. " It's very practical."

Their experimental demonstration effectively cloaked a metal cylinder from radio waves using one layer of loop antennas. The system can be scaled up to cloak larger objects using more loops, and the loops could become printed and flat, like a blanket or skin, the researchers said.

Currently the antenna loops must be manually attuned to the electromagnetic frequency they need to cancel, but in future they could function both as sensors and active antennas, adjusting to different waves in real time, much like the technology behind noise-cancelling headphones, said the researchers.

"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."

Work on developing a functional invisibility cloak began around 2006, but early systems were necessarily large and clunky, the researchers said. If you wanted to cloak a car, for example, in practice you would have to completely envelop the vehicle in many layers of metamaterials in order to effectively "shield" it from electromagnetic radiation.

The sheer size and inflexibility of the approach makes it impractical for real-world uses, they said, adding that earlier attempts to make thin cloaks were not adaptive and could work only for specific small objects.

According to the researchers, beyond obvious applications, such as hiding military vehicles or conducting surveillance operations, this cloaking technology could eliminate obstacles, for example, structures interrupting signals from cellular base stations could be cloaked to allow signals to pass by freely.

And though their tests showed the cloaking system works with radio waves, re-tuning it to work with light waves could use the same principle as the necessary antenna technology matures, they said.

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

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