Talk:Metamaterial

‹See TfM›

This article is a complete hotch-potch, and I think it would be completely useless for anyone who wanted to become familiar with this topic. By the look of things editors have been using this page to trumpet their own contributions to the field (which may or may not be relevant) rather than to provide a useful overview of the area. The problem is not helped by a lack of a good definition of a metamaterial - should it include the artificial dielectrics from the 1940's, left-handed tranmsission line media, and photonic crystals? (No Worries 05:40, 25 September 2007 (UTC))

Is the diagram correct? It appears to contradict the later statement in the article "but rays are refracted away from the normal on entering the material" whereas the diagram has the rays being refracted closer to the normal, and more surprisingly, on the other side of the normal. If the diagram is wrong can someone delete it please.

The diagram is correct; I've corrected the text. See, if N1 sin theta1 = N2 sin theta2 and N1 and N2 have opposite signs, then theta1 and theta2 must have opposite signs as well; following the usual sign convention, this means that they are on the same side of the normal. User:Ben Standeven as 70.129.35.107 06:17, 13 July 2006 (UTC)

Can/should we talk about superlenses here? Can someone at least answer some of the basic questions? Like do the concave/convex lenses work opposite from a regular lens?

Why is it that the only meta-material that is talked about is negative refractive index? Shouldn't that get its own page then?

As long as there's enough information on "metamaterial" to justify a page with that heading, negative index lenses should probably be under here. Way too easy to get a horde of small pages for many topics otherwise. As for non-NI materials, the only other case that comes to mind at present is the use of comb-shaped structures to polarize microwaves (reflects waves polarized in one direction, transmits waves polarized perpendicularly to that). Probably other examples for microwave-frequency use that I'm overlooking, but NI materials are popular because they're potentially so useful (lenses that are allegedly not diffraction-limited). --Christopher Thomas 04:36, 25 May 2005 (UTC)

Question for optics people out there - do photonic crystals (photonic band-gap structures) count as metamaterials? They seem to satisfy the definition written in metamaterial, but I might be missing some subtle distinction. --Christopher Thomas 04:37, 25 May 2005 (UTC)

No, one basic properties of metamaterials is that they are homogeneous on a wavelength scale. The interaction of the material with light must come from sub-wavelength scaled features. Photonic crystals, on the other hand, are structure with features of about one wavelength long; diffraction around these features is the main effect here. The definition of metamaterials in the article should maybe be modified to refelect this.

2nd and 3rd intro paragraphs

Hi, I couldn't follow the connection between the 2nd and 3rd paragraphs. Could some one in the know edit this article and make these two paragraphs flow better ? Thanks -kg

I took a stab at this. How does it look now? --Christopher Thomas 05:43, 26 May 2005 (UTC)

Much better! thanks! --Kaushik

Superlens

The superlens created at Berkley did not have a negative index of refraction. All materials with a negative index of refraction are for microwave frequencies. See Superlens —This unsigned comment was added by 67.189.113.62 (talk • contribs) on 03:04, 20 March 2006.

If it had a negative index of refraction for microwares, then it by defintion has a negative index of refrarction. I just does not have one for visible light, only microwave light. And don't make me explain how microwaves are light again.--Scorpion451 02:46, 25 June 2007 (UTC)

Theoretical Models, 2nd and 3rd Paragraphs

It says that a 'C' ring with is axis in the propogation direction (I assume this means the ring is flat to oncoming radiation) would produce negative permeability. In fact, this only creates negative permitivitty. Negative permeability is created when propagation is in the plane of the ring and the B field then acts perpendicular to the loop. This is not possible if the axis of the ring is alined with the propogation vector of the light. See "Stefan Linden et. al., Magnetic Response of Metamaterials at 100 Terahertz, www.sciencemag.org, Vol 306, 19th Nov 2004, pg 1351-1353" for diagrams of permeability and permitivity with different orientations in respect to the incoming light.

Although it does say that "an induced current is created and the generated field is perpendicular to the magnetic field of the light. The magnetic resonance results in a negative permeability; the index is negative as well.", this is not magnetic resonsnace; the B field would have to be in the same direction of the normal of the loop (or have a component thereof) to create a current and then the induced field could not possibly be perpendicular to the driving field (just think Lenz's Law). If I'm missing something pleae feel free to enlighten me. —The preceding unsigned comment was added by 137.132.3.12 (talk • contribs) on 07:48, 31 August 2006.

It's like a solenoid, the magnetic force is at a right angle to the current, but the looped shape distorts the field causing it to flow in the same direction as the current. The structure of the metamaterial sets up a similar situation, only it reverses the right hand rule, making it the left hand rule, and effectively making the induced field at a right angle to the driving field. Yes it's wierd, that's what makes metamaterials facinating. --Scorpion451 02:50, 25 June 2007 (UTC)

Pop Sci

According to the article "Unveiling the first invisibility shield" in Popular Science, light travels faster through a metamaterial than a vacuum. Was this a mistake? — Daniel 04:31, 21 September 2006 (UTC)

Size ambiguity

The phrase in the first line of the 2nd paragraph that reads "at least as small" is strange wording. Does that mean "at most as small"? In other words, as small or smaller? Please clarify. Unclepea 05:44, 20 October 2006 (UTC)

It means "as small as or smaller". "at most as small" would mean "as small as or larger". English doesn't make sense even if it is your first language.--Scorpion451 02:58, 25 June 2007 (UTC)

Example of Negative refraction index

Is the example at the end of the Nri paragraph correct?

"consider the following: a person submerged in a swimming pool filled with a hypothetical liquid with negative N would appear to float above the pool instead of appearing to be beneath the surface."

If the positive refraction index would make the submerged body look closer than it is, then the negative will make them appear "underneath" or even behind the view point. I think you have the idea of the Plane and the Normal the wrong way around in this example. Otherwise it's been explained very well.

Daniel --80.195.237.107 22:18, 30 October 2006 (UTC)

I see that my example of the person in the swimming pool has been removed. It was from a Scientific American article, so I'm pretty sure it was right.Rotiro 11:02, 14 March 2007 (UTC)

The negative refractive index would indeed make the swimmer appear above the water, much like a concave mirror does, although by a different mechanism.--Scorpion451 22:20, 26 June 2007 (UTC)

I'm still having trouble with the diagram showing negative refraction. My understanding, backed up by http://physicsworld.com/cws/article/news/2692 is that a positively refracting material bends light away from the normal, and a negatively refracting material bends light towards the normal. This diagram shows both materials bending the beam towards the normal, only that the negative material bends it so far that it goes past the normal. Either this is wrong, or the Wikipedia entry on "refraction" is wrong. ---posted by NobbyNobbs

NRIs -1 < N < 0?

Can somebody explain how Snell's Law holds for NRIs between minus one and zero?

If we take N₁ to be 1 and Theta₁ to be 45 degrees, then use a negative N₂, say -0.2, then solving Sin(Theta₂) = Sin(45) / (-0.2) = -3.53~ has no solutions for N₂.

I ask because a metamaterial was recently produced with refractive index -0.6 for visible (780nm, red) light, and I'm still trying to figure out what it would 'look' like. The swimming pool discussions don't make much sense to me because, how on earth can something appear to be 'below me' when I'm standing on concrete. Wouldnt I just see concrete? 222.154.97.61 09:59, 19 December 2006 (UTC)

As for what it would look like, lay a mirror on the ground and look into it. The beams of light reflected from the mirror cover up the beams of light reflected from the concrete. It's hard to explain the way the equations apply to the wierd properties of metamaterials, because they violate fundamental assumptions of the equations. It's one of those cases of the equations say the data is wrong, but the universe says that the data is right. I'm leaning toward the universe. --Scorpion451 03:07, 25 June 2007 (UTC)

I looked closer, and now I see what your problem was. If you try it, you will see that you have the same issue for any number 1>0>-1. The refractive index .2 will give the same error as -.2 It's not the negative, it's the decimal. The following is directly from the snells law page:

When light moves from a dense to a less dense medium, such as from water to air, Snell's law cannot be used to calculate the refracted angle when the resolved sine value is higher than 1. At this point, light is reflected in the incident medium, known as internal reflection.

There is a point of refraction, except its much less than 45 degrees. The angle to the normal at which you not recieve a reflection but a refraction is approximatly 11.5 degrees.

so:

$\sin ^{-1}{({\frac {{n_{1}}*{\sin {\theta _{1}}}}{n_{2}}})}=\theta _{2}$

$\sin ^{-1}{({\frac {1*sin11.5}{-0.2}})}=-89.4$ degrees

--Scorpion451 22:08, 26 June 2007 (UTC)

Breakthrough?

http://www.newscientisttech.com/article/dn10816.html 195.210.210.217 12:39, 19 December 2006 (UTC)

Possible Factual Error

In the subsection "Negative refractive index", there's a list of some cool properties of metamaterials with negative n. The last point in the list is: "Higher frequencies have longer, not shorter, wavelengths in such a material ". I've added a citation needed flag to this, as I haven't encountered it in the literature on this topic, and I have the feeling it might be incorrect. (It runs contrary to the definition of frequency, which is phase velocity/wavelength.)

Can anyone find the proper reference for this fact? (Otherwise, I think it should be deleted as a precaution...) GameGod 02:26, 2 January 2007 (UTC)

I was just wondering about that before you changed it. What would be the relationship between wavelentgh and frequency in that case, lambda = nw/c ?

18.95.7.45 20:58, 7 January 2007 (UTC) Matthieu

I'm not certain but I belive that the above fact is correct, even though it violates the C=F/W rule. I think this is due to the negative refraction index causing the particle to slow down. To put it this way, if C(phase speed)=1(just for simplicity), then in the metamaterial if it moved at half the speed it would be 1/2=F/W. If frequency is unchanged, then wavelength must double. Does this make sense? I can put it a little more clearly, I think.--Scorpion451 03:04, 25 June 2007 (UTC)

I looked more into this. You are correct that the wavelength expands when frequency decreases and vice versa. The material, however, is not metamaterial. The expanded wavelength at slower speed is seen in materials with extremely high N, such as [[Bose Einstein condensates]. See the Slow Light article.--Scorpion451 02:18, 8 July 2007 (UTC)

Dubious Science? ("infinite inertia"?)

In the opening paragraph this sentence exists: "Such unusual properties could be a negative refractive index or infinite inertia (which are not found in naturally occurring materials)."

I've gotta say, "infinite inertia" sounds like dubious science to me - generally there's not much in science that is "infinite" and if some object possessed /infinite/ inertia then either its mass or velocity was infinite, both impossible AIUI.

There's no further mention of inertia in the article, nor here on the discussion and google didn't produce anything significant regarding this phrase ... so is this "infinite inertia" just buzzwordiness ... or outright nonsense or vandalism or ...???

Anyway, just a heads up about this fishy sounding phrase ... and thanks to all who contribute and edit to wikipedia!

--wikifreeman 21:44, 17 October 2007 (UTC)

Also the statement that the doppler effect would be reversed is just hogwash. The doppler effect is a physical interaction between a signal moving through space and a receiver of that signal. A signal can only be expanded if the receiver is moving away from it, and can only be contracted if the reciever is moving towards it. The doppler effect is not effected any properties of the signal generator. Once a signal is moving through space, the doppler effect can only possibly work that way. Why is this article linked in "see also" from a real scientific article like "einstein-rosen-podolsky_bridge ?

TeraHerz metamaterial devices

I am no expert in this field, but there does not appear to be any mention of the developments at Los Alamos National Laboratory by Hou-Tong Chen, Richard Averitt, Willie Padilla and others, which resulted in the fabrication of a controllable device. I would have thought this is very significant for the future use of metamaterials. http://www.lanl.gov/news/index.php/fuseaction/home.story/story_id/9935

parellic —Preceding unsigned comment added by Parellic (talk • contribs) 17:52, 2 March 2008 (UTC)

Ameteur question

I'm just an internet-educated dropout trying to make himself feel less stupid. If this is a stupid question, just delete it and I'll go away.

The page states that "A metamaterial (or meta material) is a material which gains its properties from its structure rather than directly from its composition." How are metamaterials different from allotropes? For example, graphite and diamond are both academically pure carbon, yet are literally as different as black and white. Diamond is one of the hardest materials in nature, but graphite rubs off on a sheet of paper. Graphite conducts electricity, diamond doesn’t. Could you say that metamaterials are allotropes that do not normally exist in nature? Or compounds with structures that do not normally exist in nature?

there's a definition in the article, i guess they have to be man-made (unlike diamonds) and a combination of more than 1 naturally occuring substance (diamonds are just C), and they have to produce an "optimized combination" of 2+ responses to excitation -- seems a ludicrously specific definition that gets us down to just the negative N materials CarlosRodriguez (talk) 05:56, 11 August 2008 (UTC)

?Vandalism

I'm new to this, but under External Links | Research groups (in order of importance), the number one spot is occupied by a site which appears to have nothing to do with Metamaterials. Maybe someone can correct this?72.90.243.147 (talk) 16:08, 5 April 2008 (UTC)

Yes, I agree. This appears to be vandalism. I have been going over the history of this page. There are a lot of changes by more than one anonymous IP address and so it is a little difficult to determine what is valid and what is not. From reading the "Oscar" dude's website, I do not believe he has anything to do with metamaterials. I am going to send him an email asking if he does. I am not sure if this "Oscar" guy is the source of the changes or not. He may not be aware of these edits at all. Anyway which way, the research groups should be listed alphabetically.The-tenth-zdog (talk) 06:38, 6 April 2008 (UTC)

Article quality

This entire article is hard for someone not already familiar with its concepts to understand. Although it has the virtue of having good spelling and of being grammatical, it could benefit from a complete rewrite due to its confusing and overly terse content and style. The final paragraph is particularly infelicitous. It and many others could also benefit from the addition of line drawings or other diagrams.

An example of an article of similar speciality and difficulty that is nevertheless easier for a nonspecialist to understand, due to its clear writing and its use of diagrams, is Block cipher modes of operation.

While it is certainly useful for an encyclopedia article to be accessible only by specialists in its field, it is even more useful if each article were understandable by a much wider audience. Then, besides being informative, the encyclopedia might also be tutorial, which greatly enhances its usefulness to society. David (talk) 14:13, 16 August 2008 (UTC)

Merge from Cloaking device

I have merged the section Metamaterial research from the article Cloaking device into the section Development and applications. I also split the section "Development and applications" into subsections to present the ideas in a more organized fashion. Please centralize discussion regarding this merge on this talk page, and feel free to change anything I merged. — OranL (talk) 04:06, 21 August 2008 (UTC)