Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Metamaterials and Left-handed Materials

  1. Mar 7, 2008 #1
    I was at a high school science symposium, and some kid presented about metamaterials, a structure that shows a negative index of refraction, n. So I think his project was pretty good and all, and he had a good understanding: he had apparently created a new composite structure with neg. n without using split ring resonators.

    But in the questions session, I was surprised that some judge totally flamed him. He thought that a metamaterial was impossible to construct, and he questioned the presenter on how a wave could travel in one direction, and carry it's energy in another. I see now that this is a consequence of the reversed Poynting vector in a metamaterial. Anyone care to explain how this is possible?

    Another few questions I had:

    What are the properties of a material with only one parameter of permittivity or permeability is negative? I know n is equal to the root of permittivity and permeability, so how can you take the root of a negative number?

    Also, what is the difficulty in creating a LHM in the optical frequencies?

    Thanks for help!
     
  2. jcsd
  3. Mar 7, 2008 #2

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Er.. are you sure a "kid" created such a thing? How in the world was he able to do it without using split-ring resonator? What element causes the negative magnetic permeability? How did he test it? At what frequency? Did he have a horn antenna for a pickup? Did he show a transmission curve?

    I had a graduate student who had to build such a thing to work in the microwave range. It isn't trivial. Even testing it isn't trivial!

    Zz.
     
  4. Mar 7, 2008 #3
    He used two perpendicular cross wire resonators.

    He said that as long as these copper wires didn't touch, they would act as an interacting pair. Something about an LC resonator. At a frequency higher that the resonance frequency, permeability is drawn negative by the magnetic field. I think his design worked at 12.5 GHz.

    But, how does the Poynting vector make sense?
     
  5. Mar 7, 2008 #4
    Oh, I also should mention, looking at his abstract, that he had source and receiving dipoles to find the strength of the exiting waves.
    I think he had a transmission map to find the resonance frequency.

    He generated a EM wave field strength map, and found a focus point.
     
  6. Mar 7, 2008 #5

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    That won't produce negative permeability. I know. That's what we constructed. We had wire arrays. But this only produces negative permittivity. That's why we also needed an array of split-ring resonators that were etched on printed-circuit boards.

    Zz.
     
  7. Mar 7, 2008 #6
    OK, so I guess the presenter didn't really do anything. He found a focusing point to the waves on the opposite side of the lens, though, somehow.

    But how about Poynting vector? And why is it difficult to create a LHM at optical frequencies? Also, what about materials with only one parameter negative?

    Zz, may I ask where you've done work with metamaterials? Since it's new, I imagine only a few institutions work with it.
     
  8. Mar 7, 2008 #7

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    It is not that simple.

    If he was looking only at the transmission, he need to show two different curves first. He has to show, using the wires, that in the frequency range where the permittivity is negative, there's no transmission. Then he has to show, using the split-ring resonators, that in the range where the permeability is negative, there's also no transmission. Now, here's where it gets tricky. He has to hope that, based on his construction, these two ranges overlap!. If they do, then when they are put together as a single structure, somewhere where they overlap, what used to be no transmission now actually show a transmission. This is one evidence for such left-handed property.

    Zz.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Metamaterials and Left-handed Materials
  1. Hand through table? (Replies: 30)

Loading...