Invisibility cloaks have been around in various forms since 2006, when the first cloak based on optical metamaterials was demonstrated. The design of cloaking devices has come a long way in the past seven years, as illustrated by a simple, yet highly effective, radar cloak developed by Duke University Professor Yaroslav Urzhumov, that can be made using a hobby-level 3D printer.

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As envisioned by Harry Potter and DARPA, invisibility cloaks are an important new direction for camouflage technology. In contrast to conventional stealth technology, which concentrates on reducing the detection signature (radar cross section, heat signatures, optical detection, etc.) of an object, invisibility cloaks work by making it seem as if radar and light flows around the cloaked object. When successfully accomplished, neither the cloaked object nor the cloak will be detected.

How a cloak works can be illustrated by an analogy offered by Duke University Professor David Smith. Imagine a fabric in which the threads are optical fibers. As seen on the left of the image below, light will travel freely from one edge to the opposite edge of a piece of this fabric. If an opaque object is placed so that it blocks some of the light, it is equivalent to cutting a hole in the optical fiber fabric, as seen in the top right-hand image.