This composite illustration shows a cutaway of the cloak with the square array of tubes on the left. The object to be cloaked is the red sphere, which is being pushed up into the cloak by the spring. The colours on the right show the changes in the electromagnetic properties of the cloak that result from the mechanical distortion caused by the object. (Courtesy: Kyoungsik Kim)

Smart cloak deforms to keep objects invisible

Nov 23, 2012

An adaptable “invisibility cloak” that hides objects even as they change shape has been unveiled by researchers in the US and South Korea. The metamaterial-based design works within a range of microwave frequencies and remains insensitive to changes in shape of up to 8 mm. This marks a significant departure from traditional cloaks, which have to be redesigned to compensate for even small changes in the shape of an object. In addition, the new device covers a larger relative range of frequencies than has been achieved with previous cloaks.

Most invisibility cloaks take advantage of the strange properties of metamaterials – collections of structures that are assembled so that they interact with electromagnetic radiation in very specific ways. One useful property of some metamaterials is a negative index of refraction, which can be used to guide radiation smoothly around an object in much the same way that water flows around a stone in the middle of a river. For a cloak working in the visible portion of the electromagnetic spectrum, our eyes would only detect light that appears to have travelled in a straight line from the space behind the cloaked object, rather than as having travelled around it. Therefore the object would appear invisible.

Read more: Smart cloak deforms to keep objects invisible – physics world.

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