User:Steve Quinn/Former MM content of Wikipedia

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In electromagnetism (covering areas like optics and photonics), a meta material (or metamaterial) is an object that gains its (electromagnetic) material properties from its structure rather than inheriting them directly from the materials it is composed of. This term is particularly used when the resulting material has properties not found in naturally formed substances.

In order for its structure to affect electromagnetic waves, a metamaterial must have features with size comparable to the wavelength of the electromagnetic radiation it interacts with. For visible light, this is on the order of one micrometre; for microwave radiation, this is on the order of one decimetre. An example of a visible light metamaterial is opal, which is composed of tiny quartz spheres. Photonic bandgap materials are an example of an artificial visible light metamaterial. Microwave frequency metamaterials are almost always artificial, constructed as arrays of current-conducting elements (such as loops of wire) that have suitable inductive and capacitive characteristics.

• 16:56, 14 December 2005 (below)

Pendry was the first to imagine a practical way to make a left-handed metamaterial(LHM). He thought about metallic wires in propagation direction to provide the negative permittivity (ε<0). Nevertheless, natural material exist with a negative permittivity typically ferroelectrics. The challenge came from the negative permeability (µ<0). He showed that an open ring (C shape) which axis is in the propagation direction could provide a negative permeability . In the same paper, he showed that a periodic array of wires and ring could endow with negative index.

The analogy is the following: natural materials are made of atoms, which are dipoles. These dipoles modify the light velocity of a factor n (the refractive index). The rings and wires units play the role of atoms. Wire acts as a ferroelectric atom. The ring acts as an inductance L and the open section as a capacitor C. So the whole ring can be considered as a LC circuit. When the electromagnetic field pass through the ring, an induced courant is created and the generated field is perpendicular to the magnetic field of the light. There is a magnetic resonance so the permeability is negative, and the index is negative too.

• 16:56, 14 December 2005 (above)

Negative refractive index

Very nearly all materials encountered in optics, such as glass or water, have positive values for both permittivity $\epsilon$ and permeability $\mu$. However, many metals (such as silver and gold) have negative $\epsilon$ at visible wavelengths. A material having either (but not both) $\epsilon$ or $\mu$ negative is opaque to electromagnetic radiation (see surface plasmon for more details).

Although the optical properties of a transparent material are fully specified by the parameters $\epsilon$ and $\mu$, in practice the refractive index $N$ is often used. $N$ may be determined from $N={\sqrt {\epsilon \mu }}$. All known transparent materials possess a positive index because $\epsilon$ and $\mu$ are both positive.

However, some engineered metamaterials have $\epsilon <0$ and $\mu <0$; because the product $\epsilon \mu$ is positive, $N$ is real. Under such circumstances, it is necessary to take the negative square root for $N$. Physicist Victor Veselago proved that such substances are transparent to light.

Metamaterials with negative $N$ have numerous startling properties:

• Snell's law ($N_{1}\sin \theta _{1}=N_{2}\sin \theta _{2}$) still applies; but rays are refracted away from the normal on entering the material
• The Doppler shift is reversed (that is, a light source moving toward an observer appears to reduce its frequency)
• Cerenkov radiation points the other way
• group velocity is antiparallel to phase velocity (as opposed to parallel for normal materials)

One common metamaterial is the Swiss roll.

Such metamaterials follow a "left-hand rule".

The first Superlens (an optical lens employing negative refraction with vastly improved microscopic resolution) was created and demonstrated in 2005 by Xiang Zhang et al of UC Berkeley, as reported in the April 22 issue of the journal Science [1]

External Links

• Experimental Verification of a Negative Index of Refraction