Debashis Chanda at the University of Central Florida (UCF) has created a way to bend light with artificial nanostructures to develop an invisibility cloak.
Chanda and other nanotech experts have developed a large swath of a “multilayer 3-D metamaterial” that operates “in the visible spectral range”.
This was accomplished by “using nanotransfer printing, which can potentially be engineered to modify surrounding refractive index needed for controlling propagation of light.”
“Such large-area fabrication of metamaterials following a simple printing technique will enable realization of novel devices based on engineered optical responses at the nanoscale.”
In 2013, the Department of Electrical and Computer Engineering (DECE) at the University of Toronto (UoT) have revealed researchers created a cloak that is thin, scalable and adaptive to various objects and sizes to hide an object to radar detection.
So far, the object is still visible to the human eye; however this “practical” approach is being hailed as a step toward an actual invisibility cloak.
“We’ve demonstrated a different way of doing it. 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.”
Indeed, the array of small antennas that expel the electromagnetic field surrounding the cloak cause the “invisibility” that renders the object un-seeable to radar systems.
Called an active electromagnetic cloak (AEMC), this device “uses an array of elementary sources to cancel the scattered fields created by an object. An active interior cloak does this by placing the sources along the boundary of the object.”
This technology “can be thought of as introducing a discontinuity in the field to cancel out the scattered field by the object.”
The process of cloaking was explained as:
“Picture a mailbox sitting on the street. When light hits the mailbox and bounces back into your eyes, you see the mailbox. When radio waves hit the mailbox and bounce back to your radar detector, you detect the mailbox. [Professor George] Eleftheriades and [PhD student Michael] Selvanyagam’s 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.”
“Our active cloak is a completely new concept and design, aimed at beating the limits of [current cloaks] and we show that it indeed does. If you want to make an object transparent at all angles and over broad bandwidths, this is a good solution. We are looking into realizing this technology at the moment, but we are still at the early stages.”
Seven years ago, the first “invisibility cloak” was revealed that could “bended microwaves around a small copper cylinder which allowed it to vanish.”
“If you suppress scattering in one range, you need to pay the price, with interest, in some other range. For example, you might make a cloak that makes an object invisible to red light. But if you were illuminated by white light (containing all colours) you would actually look bright blue, and therefore stand out more.”
The team at UoT, under Alu, have introduced “the concept and practical design of broadband, ultrathin cloaks based on non- Foster, negatively capacitive metasurfaces. By using properly tailored, active frequency- selective screens conformal to an object, within the realm of a practical realization, is shown that it is possible to drastically reduce the scattering over a wide frequency range in the microwave regime, orders of magnitude broader than any available passive cloaking technology. The proposed active cloak may impact not only invisibility and camouflaging, but also practical antenna and sensing applications.”