Invisibility cloaks are almost a reality after scientists invent ultra-thin material that hides objects from microwaves

Scientists have developed an ultra-thin material that hides objects from microwaves – bringing the possibility of invisibility cloaks much closer. Up until now, invisibility cloaks put forward by scientists have been fairly bulky contraptions – an obvious flaw for those interested in replicating Harry Potter’s magical clothing. However, researchers have now 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.  The researchers, from the University of Texas in the United States, have used a new, ultra-thin layer called a ‘metascreen’.
The metascreen cloak was made by attaching strips of copper tape to a flexible polycarbonate film. It was used to cloak an 18cm 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 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. Study co-author Professor Andrea Alu said: ‘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.  ’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.’ Last year, the same group of researchers were the first to successfully cloak a 3D object in another paper also published in New Journal of Physics, using a method called ‘plasmonic cloaking’, which used more bulky materials to cancel out the scattering of waves.
Now one of the key challenges for the researchers will be to use ‘mantle cloaking’ to hide an object from visible light. ’In principle this technique could also be used to cloak light,’ said Professor Alu. ’In fact, metascreens are easier to realise at visible frequencies than bulk metamaterials and this concept could put us closer to a practical realisation.  ’However, the size of the objects that can be efficiently cloaked with this method scales with the wavelength of operation, so when applied to optical frequencies we may be able to efficiently stop the scattering of micrometer-sized objects. ’Still, we have envisioned other exciting applications using the mantle cloak and visible light, such as realising optical nanotags and nanoswitches, and noninvasive sensing devices, which may provide several benefits for biomedical and optical instrumentation.’

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