User talk:RFenginerd
Welcome
[edit]
|
Negative index metamaterials
[edit]Hello. I appreciate your additions and I responded to you over at the talk page of Transformation optics. Regarding negative index metamaterials, you wrote: Dispersion with frequency is a necessary but not sufficient condition for a negative index. I have seen this before in another article. It is really not clear, what you are attempting to say. Also, the not so well informed reader will probably have no idea either. First, what does this mean? Second, please keep in mind we are writing for other people. This realization dawned on me at some point after I started editing so this is easy to forget. Especially, when the scientific language is so accurate compared to popular press descriptions a lot of times. I am discovering if I use, or research, a mix of materials such as peer reviewed articles, text-book-type books, and magazine write ups I can get a better sense of what to communicate. Hopefully, I am being helpful. Anyway, thanks for your interest and contributions. ----Steve Quinn (formerly Ti-30X) (talk) 06:55, 27 May 2010 (UTC)
Also, regarding this same article the content added in the section entitled Original proposal appears to be outside of the scope of the reference for this particular section. The view is from permittivity and permeability. In other words, these are the parameters of interest in the cited journal article. And the journal article states, "To describe the EM properties of a material, two important parameters are introduced, that is, electric permittivity ε and magnetic permeability μ. In principle, if the ε and of materials are known, then the propagation of EM waves inside materials, or the EM phenomena at the surface between two materials can be well predicted."
In the second paragraph of the Wikipedia article, Negative index metamaterials, refraction is discussed as a phonomenem at the interface. And so does the journal article. Although stating there are other independent parameters may be true, it outside the scope, and dilutes the point that is being made. This may seem too narrow, but it is what works best at Wikipedia. Thanks.----Steve Quinn (formerly Ti-30X) (talk) 07:21, 27 May 2010 (UTC)
- I moved your brief addition in the first paragraph into a new section, just below the first section. The section is entitled Refractive index and impedance. so now we need sources for this discussion. What do we need to say about these parameters, while keeping the focus of the section on NIMs? I am guessing you have some ideas. ----Steve Quinn (formerly Ti-30X) (talk) 14:45, 28 May 2010 (UTC)
- Discussion of these parameters, in this context, had not occured to me. I am glad you brought this up. ----Steve Quinn (formerly Ti-30X) (talk) 15:06, 28 May 2010 (UTC)
- Good thoughts. Part of this was inspired by the confusion of discussing the effective medium concept with someone and which parameters can be negative. I think that's where this best fits, whether in the negative index article or elsewhere. Things to the effect of:
- the fact that there aren't any physical restrictions exactly placed on solely either epsilon or mu, the restrictions arise when you apply Maxwell's eqns. The often-stated "epsilon can't have an imaginary part with a certain sign" isn't accurate. Once you define a sign convention, either jwt or -iwt, you set the sign of the imaginary part of the refractive index/wavevector to prevent exponential growth. That's one physical restriction.
- the impedance has to be positive, again from Maxwell's, to prevent problems with sign changes and field growth at media interfaces
- so there are restrictions on allowable values of epsilon and mu, just not ones you can tell by inspection. I have a couple sources in mind that address this from the metamaterial perspective and the validity of retrieving the material parameters
- I don't know if you've done any simulation/measurement or whatever, but the procedure is pretty well-defined. If you are familiar, feel free to skip this bullet. You measure either transmission or reflection coefficients (or S11 and S21). S parameters are more common with EEs, T/R with physicists/optical people. Then you calculate values of effective impedance and index. If you start from the physical picture, like a flow diagram for S parameters, you can derive equations in terms of n and Z. Depending on the exact path you take they end up with some combination of square roots, inverse cosines, and logs - since you're using complex functions as arguments, you have to choose the correct branch cuts for these functions since they're not single-valued. Most of the choices are dictated by selecting physical values, meaning n and Z, so the retrieved effective eps/mu aren't determined first. It's far more common to determine a set of n and Z and then use the relationships between them and eps/mu to calculate eps/mu. Of course, the problem comes in the real part of n - it ends up being a log or arccos of a complex number, and the imaginary part of the log corresponds to real(n). Since real(n) doesn't have physical restrictions from Maxwell's, the branch has to be chosen carefully (have a couple references in mind here also). And of course this directly relates to negative index metamaterials. I'm not sure if this is a bit technical for WP in the relatively early stage of these articles - it's been discussed pretty well. The most-cited references are from Smith and Chen/Chan (can't remember if it's Chen or Chan).
- So I'm thinking that a discussion of this type of thing is important (nigh critical) for someone trying to actually understand metamaterials. I'm not sure where it fits best, or if it's better to hold off for a while on a discussion that will inevitably end up a bit technical. I'm guessing people will come to this article and have questions about the validity, given that they're always told that real(n)>0 and imag(eps or mu) is some set sign. This could help clear up the confusion for people who are familiar with EM but not necessarily metamaterials at all. Of course, adding in the complex analysis bit doesn't help accessibility.
- Good thoughts. Part of this was inspired by the confusion of discussing the effective medium concept with someone and which parameters can be negative. I think that's where this best fits, whether in the negative index article or elsewhere. Things to the effect of:
I haven't added references for all my edits yet on NIM or transformation optics pages etc, but do have some definite ones in mind. Feel free to add cite tags, which will help me remember where they need to be.RFenginerd (talk) 00:29, 29 May 2010 (UTC)