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Illusion device hides objects, conjures up "ghosts"

10 April 2013

How the ghosting technology works: (a) The original object. (b) The object covered by the designed ghost device, metamorphosing scattering feature of the original object. (c) A shrunken object at the original centre with two side "ghost" objects, whose signature is identical to (b).

The experimental proof-of-concept: (a) Parallel-plate waveguide mapping system. (b) Close-up of the "ghost-illusion" device. The device is made from specially designed metamaterials, with eight concentric layers of circuit boards. The printed structures in Region II are designed in a special way such that those parts can effectively cancel the original scattering of the central object while producing a new "ghost" scattering centre. Thus, the viewer will only "see" the "ghost" objects which are physically non-existent.

Dr Qiu (right) and Dr Han with the fabricated ghost device

It may not be Harry Potter's invisibility cloak, but NUS researchers have engineered a device that hides an object and brings up "ghosts" in its place. An item subjected to the "magic" of the invention gives the illusion of a totally different entity - say, a bag takes on the guise of a ball. The technology has the potential to be scaled up for things as large as an aeroplane, painting an intriguing scenario in defence where a fighter plane is camouflaged to look like a commercial airliner.

Led by Dr Qiu Cheng-Wei, a team at the NUS Department of Electrical and Computer Engineering developed an optical device that is able to generate "ghosts" through optic scattering and specially formulated artificial metamaterials. Fabricated from printed metallic structures, the novel materials have properties that can manipulate light to behave abnormally. The geometric shape, locations and equivalent material properties of these ghostly images can be pre-designed and manoeuvred such that they show up in spaces different from the actual sites of the real object.

To date, "ghosting" experiments with metamaterials have limited success in visually altering an object and controlling where its "ghost" manifests. In addition, only a single "ghost" can be made, in the same position of the original item.

Thus the NUS group's breakthrough of creating more than one virtual "ghost" image from the actual object holds greater significance and exciting implications. Furthermore, the technology can cause the real thing or person to "disappear", calling up instead images that are controllable in looks, shapes or sizes. Theoretically, there is no dimension or frequency range restriction based on this technology. Only the fabrication capability will be the "glass ceiling", said Dr Qiu.

"As our work solves several major issues associated with 'ghost' illusion, we believe it will pave the way for future applications of advanced optical illusion, camouflage and cloaking - in an interestingly new sense. It has enormous potential to enhance our ability to mould, harness and perceive electromagnetic wave at will," he added.

The latest findings conjure up visions of unimaginable possibilities for deception in the fields of defence and security. The knowledge also provides the basis for the development of new optical and microwave products such as for detection, surveillance and communication. The project has received defence agency funding to further enhance the technique to build larger microwave devices to achieve radar "ghosts" and aircraft camouflage.

The report, co-authored with NUS' Dr Han Tiancheng, together with China's Southeast University in Nanjing and UK's University of Birmingham, has been recently published in Advanced Functional Materials.