Could this invisibility cloak be the military's best ally? Device uses electromagnetism to make objects invisible to radar systems

Engineers have surrounded an object with small antennas that collectively radiate an electromagnetic field, cancelling out waves scattered off it

The University of Toronto researchers believe their innovation could be used to hide military vehicles and to conduct surveillance operations



As the technology advances, it could also be adapted to make objects invisible to the human eye too

Scientists are currently competing to create the best invisibility cloak, as imagined in films such as Harry Potter and Star Trek.



As yet, no-one has managed to replicate a flexible cloak as worn by the boy wizard, or the cloaking device used by the Kingons to make their ships invisible to another starship's sensors, but two Canadian scientists have created an invisibility cloak that they say is thin and adaptive to different types and sizes of objects.

Unlike other recent cloaks that rely on planes of glass simply bending light in a way that renders small objects temporarily invisible, the researchers have taken an electrical engineering approach, which makes objects undetectable to radar.

This is the set up of the lab where Professor George Eleftheriades and Michael Selvanayagam have designed and tested a new approach to cloaking - by surrounding an object with small antennas that collectively radiate an electromagnetic field. The radiated field cancels out any waves scattering off the cloaked object

They said as the technology advances, it could also be adapted to make things invisible to the human eye too.



HOWS DOES IT WORK?

Usually, when radio waves hit an object, they bounce back to a radar detector and reveal its identity and location.



To overcome this, the engineers surrounded an object with small antennas that collectively radiate an electromagnetic field, away from the object.



The radiated field cancels out any waves scattering off the cloaked object, rendering the object invisible to radar.

Professor George Eleftheriades and PhD student Michael Selvanayagam have designed and tested a new approach to cloaking, by surrounding an object with small antennas that collectively radiate an electromagnetic field.

The radiated field cancels out any waves scattering off the cloaked object, rendering the object invisible to radar, explained the two researchers at the University of Toronto.





‘We've taken an electrical engineering approach, but that's what we are excited about," said Professor Eleftheriades. ‘It's very practical.’



When light hits an object, such as a postbox and bounces back into a person’s eyes, they can see it and similarly, when radio waves hit the object, they bounce back to a radar detector and reveal it is a postbox, in a certain location.



The scientists’ 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.



Usually, when radio waves hit an object, they bounce back to a radar detector (illustrated) and reveal its location. The engineers surrounded an object with small antennas that collectively radiate an electromagnetic field, which cancels out any waves scattering off the cloaked object, rendering the object invisible to radar

While hiding post boxes might not have any immediate military applications, the technology could be used to create a next-generation devices to cloak vehicles.



Professor Eleftheriades said he and Mr Selvanayagam have demonstrated a new way of cloaking objects.



‘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.’



In their experiment, described in the journal Physical Review X, they effectively cloaked a metal cylinder from radio waves using one layer of loop antennas.



The duo said their 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.



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.



The ultimate camouflage? The engineers said their technology could be used to make military vehicles (pictured) undetectable to radar systems and the innovation could one day be applied to light, as well as radio waves, potentially making a tank invisible to the human eye

The pair began developing a functional invisibility cloak began around 2006, but their early systems were necessarily large and clunky –to cloak a car, an individual had to completely envelop the vehicle in many layers of metamaterials to ‘shield’ it from electromagnetic radiation.



The size and inflexibility of the approach makes this technique impractical for real-world uses, while earlier attempts to craft thin cloaks were not adaptive and could only work for specific, small objects.



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



The system can also alter the signature of a cloaked object, making it appear bigger, smaller, or even shifting it in space.



Their tests showed the cloaking system works with radio waves but could also work with light waves in the future, using the same principle as the antenna technology matures, which could mean objects could be invisible to the human eye.

‘There are more applications for radio than for light,’ Professor Eleftheriades said.

