Invisibility cloak to make objects invisible to radar systems

Scientists have demonstrated an effective invisibility cloak that is thin, scalable and adaptive to different types and sizes of objects.
Professor George Eleftheriades and research student Michael Selvanayagam from the University of Toronto 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.
"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," Eleftheriades said.

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 Eleftheriades said 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.
Work on developing a functional invisibility cloak began around 2006, but early systems were necessarily large and clunky. Earlier attempts to make thin cloaks were not adaptive and active, and could work only for specific small objects.

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.
The system can also alter the signature of a cloaked object, making it appear bigger, smaller, or even shifting it in space.
And though their tests showed the cloaking system works with radio waves, re-tuning it to work with Terahertz (T-rays) or light waves could use the same principle as the necessary antenna technology matures.
The study was published in the journal Physical Review X.