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Illustration of a pair of shoes casting the shadow of a person.
Illustration by Karolis Strautniekas

A Way to Make Things Disappear

Prof. George Eleftheriades is developing a radar-evading technology that he thinks could be used one day to make anything invisible

In the world of Harry Potter, wizards who want to disappear simply put on a magic cloak that renders them invisible.

No such garment exists in our world (yet), but a U of T engineering professor is working on a material that could be wrapped around an object to make it undetectable to radar. And he thinks the same technology could be used to make anything – even a human being – invisible to the naked eye.

“It’s a matter of putting the resources together and focusing on that goal,” says George Eleftheriades, who is also director of the Centre for Reconfigurable Electromagnetic Surfaces.

Making an object invisible – whether to radar or the human eye – relies on the same principle of reflection.

When light hits an object and bounces back, the eye sees the reflection. In the case of radar, an antenna sends out radio waves that hit an object and then bounce back to a receiver. This equipment can determine the size, range and speed of the object and then present the information on a screen.

Some airplanes use “stealth technology” comprising a unique shape and surface material to absorb and redirect the radio waves. But they can still be illuminated by radar devices acting together from different angles.

The innovation Eleftheriades and his researchers have developed is an “active cloaking technology” that uses tiny antennas to emit signals matching the radar wave frequency. This leaves the incoming waves undisturbed. “It’s as if the waves are passing right through the object,” says Eleftheriades.

Over the next two years, he and his research team plan to develop a thin, flexible material embedded with these antennas that could be wrapped around any size or shape of object to hide it from radar.

They are also working on fine-tuning the cloaking signals so they can be adjusted in real time to match different incoming radio waves – much like how noise-cancelling headphones mute fluctuating sound waves.

Although the technology’s military applications are clear, Eleftheriades sees potential commercial uses as well. For example, structures that impede cellphone transmissions could be cloaked to allow these signals to pass freely.

Adapting the technology to make objects invisible to the human eye would be more complex but far from impossible, he says.

Instead of using microwaves to cancel incoming radio waves, the antennas would emit waves of light to match and cancel any visible reflection travelling back to the human eye.

The challenge is huge: there would have to be millions of antennas embedded in the material (instead of thousands) and they would have to be much smaller. The cloak would need a reliable power source and would have to be able to match incoming light waves as they fluctuate in real time.

To be practical for humans, the cloak would also have to be extremely thin and flexible. “But we could do it in five to 10 years with a dedicated effort,” says Eleftheriades. “A computer chip has billions of transistors in it, so we already have shown we can master this kind of complexity and scale.”

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