Mike Raiford <mra### [at] hotmailcom> wrote:

> The only thing I have seen so far that even remotely fits the
> meta-materials description (with negative refraction) is something on
> the scale of microwaves (which looks like a grid of printed circuit
> boards), unless opal does. Opal seems to show irridescent-like
> properties (gee, opalescense?), but none of the weirder properties that
> the described metamaterial has. I don't know if microwaves refract in
> the same fashion as light does, though I'm sure there are theoretical
> materials that refract microwaves.

I think opal is mentioned because it fits the definition of a metamaterial,
which according to wikipedia etc is "an object that gains its
(electromagnetic) material properties from its structure rather than
inheriting them directly from the materials it is composed of." So probably
all materials with negative refractive indices are metamaterials, but not
all metamaterials have negative refractive indices.

The effect was first demonstrated with microwaves, because to create these
bizarre materials you need to alter their electromagnetic properties on
distances that are roughly the same size as the wavelength of the radiation
involved. If you use microwaves, you can take advantage of the wavelengths
being on the order of millimetres to centimetres, and fabricate your
metamaterial on a circuit board in civilised surroundings and with easy
ways to check it's all working.

There's no theoretical reason why this shouldn't work with light, despite
the wavelengths being 100,000 times smaller, but in practice it's obviously
many times more difficult to do this on such small scales. Recently a group
got it to work, though:

http://www.eurekalert.org/pub_releases/2005-04/uoc--nso041805.php

It also seems that one group got it to work with ultrasound!

http://www.eetimes.com/showArticle.jhtml?articleID=47902254

Plenty of common materials refract microwaves. It works the same way as for
light (except that diffraction and wave effects are much more obvious). You
can make a microwave lens out of quite ordinary stuff, most dielectrics will
work I imagine.

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