Up until now, the invisibility cloaks put forward by scientists have been fairly bulky contraptions – an obvious flaw for those interested in Harry Potter-style applications. However, researchers from the US have developed a cloak that is just micrometres thick and can hide three-dimensional objects from microwaves in their natural environment, in all directions and from all of the observers’ positions.
Researchers from the University of Texas at Austin, have used a new, ultra-thin layer called a “metascreen.” The metascreen cloak was made by attaching strips of 66 micrometre-thick copper tape to a 100 micrometre-thick, flexible polycarbonate film in a fishnet design.
It was used to cloak an 18 cm cylindrical rod from microwaves and showed optimal functionality when the microwaves were at a frequency of 3.6 GHz and over a moderately broad bandwidth. The researchers also predict that due to the inherent conformability of the metascreen and the robustness of the proposed cloaking technique, oddly shaped and asymmetrical objects can be cloaked with the same principles.
Objects are detected when waves – whether they are sound, light, x-rays or microwaves – rebound off its surface. The reason we see objects is because light rays bounce off their surface towards our eyes and our eyes are able to process the information.
Whilst previous cloaking studies have used metamaterials to divert, or bend, the incoming waves around an object, this new method, which the researchers dub “mantle cloaking,” uses an ultra-thin metallic metascreen to cancel out the waves as they are scattered off the cloaked object.
“When the scattered fields from the cloak and the object interfere, they cancel each other out and the overall effect is transparency and invisibility at all angles of observation,” said co-author, Professor Andrea Alu.
“The advantages of the mantle cloaking over existing techniques are its conformability, ease of manufacturing and improved bandwidth. We have shown that you don’t need a bulk metamaterial to cancel the scattering from an object – a simple patterned surface that is conformal to the object may be sufficient and, in many regards, even better than a bulk metamaterial,” said Alu.