Cloaking Device Can Conceal an Object from Electromagnetic Radiation in the Microwave Range

When a beam of incoming microwaves hits the flat, mirror-like surface, it is reflected (A), but when it hits a bump on the surface, the radiation scatters (B). Placing the cloaking material on top of the bump "restores" the mirror, so that the beam is reflected as if it had hit a flat surface (C). Panels D-F show the same cloaking effect with difference wavelengths.

[Image courtesy of AAAS/Science]

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Researchers have created an invisibility cloak of sorts, though it looks more like a yellow bathmat than Harry Potter's famous cloth. The material, described in the new issue of Science, can conceal an object from electromagnetic radiation in the microwave range when the object itself is covered in a reflective metallic coating.

Study author David Smith of Duke University says this type of electromagnetic cloaking might prove useful for enhancing communications, so that the radio frequency (RF) signals from cell phones, for example, might be guided around objects that would otherwise impede them.

In contrast to the cloak the authors described in a previous Science article (published online 18 October 2006 and in print 10 November 2006), the new and much more complex material works over a broad band of microwaves and may therefore be more easily adapted for visible light.

Cloak lying over a bump on a flat surface. Both the bump and surface are covered in a reflective coating. The cloak makes it appear that microwaves hitting the bump are actually reflecting off a flat surface.

[Image courtesy of Jack Mock]

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The researchers' setup includes a flat mirror, which alone would reflect a beam of incoming microwaves. An object, also coated in a mirror-like coating, is placed on the flat surface. Without any cloaking device, this bump would cause the microwaves to scatter. But, placing the cloaking material on top of the bump "restores" the mirror, so that the beam is reflected as if it had hit a flat surface.

The material itself is a "metamaterial," an engineered composite material whose electromagnetic properties can be tuned by manipulating its geometry. It was constructed from thousands of individual units, each designed and fabricated by an automated process.

Although different objects could theoretically be placed inside the shell or "bump" the authors used in their study, changing the size or shape of the bump would require a new version of the material designed specifically to conceal that shape.

Kathleen Wren

15 January 2009