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.
Researchers said: “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.”
Andrea Alu , professor at the University of Texas (UoT), commented : “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.”
Alu said: “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.”
In 2012, Hyperstealth announced they have developed SmartCamo, a material that can conceal the wearer by matching their surroundings.
By bending light, the SmartCamo uses nanotechnology “so the object might be invisible to microwaves or infrared” – yet not simultaneously.
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