Radiation-soaking metamaterial for stealth


Nov 16, 2009
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This material really does deserve to be labelled the new black - it absorbs virtually all the light that hits it.

This "blacker than black" stuff is an example of a class of substances known as metamaterials, which exhibit optical properties not normally found in nature.

Metamaterials consist of a regular array of two or more tiny components, each smaller than the wavelengths of the light they interact with. It is this array-like internal structure that gives them their unusual properties.

Evgenii Narimanov of Purdue University in West Lafayette, Indiana, realised that it should be possible to design a metamaterial with the right internal structure to absorb virtually all the electromagnetic radiation in a particular range. An object made of such a material would effectively be perfectly black. By contrast, ordinary black objects always reflect a little light.

In collaboration with Narimanov, Mikhail Noginov and colleagues at Norfolk State University in Virginia have now created such a perfectly black material. It consists of silver wires 35 nanometres in diameter, embedded in 1-centimetre squares of aluminium oxide, 51 micrometres thick.

The team tested their handiwork by illuminating polished and roughened versions of the material with near-infrared radiation at a wavelength of around 900 nanometres, just beyond the red end of the visible spectrum. With the radiation hitting the material at an angle less than 45 degrees from the perpendicular, they found that 20 per cent of it was reflected if the surface was polished, though the proportion dropped to less than 1 per cent if it was roughened.

The concept is "equally applicable to all parts of the electromagnetic spectrum", Narimanov told a session of the Conference on Lasers and Electro-Optics last month in San Jose, California. "This is a new and valuable result," says metamaterial pioneer John Pendry of Imperial College London.

Narimanov said the primary application of this type of material is likely to be military, for use in "stealth technology in the gigahertz range" - in other words, to build equipment invisible to radar.


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