Meta Materials: Time

  1. I am new to the forums, so hi.

    I have been woundering about meta materials. From what I know, meta-materials are extremly small objects that are able to bend light because of their unique shapes. Some have demonstrated how they can be placed to cause an invisibility cloak by having the light bend around the object so the light goes around and out at the same place it would have if the object was not there.

    The question I have been thinking about is whether you can use meta materials to bend light around the object completly, so the light just keeps going in a circle around the object. I thought of this because a professor, Ronald Mallett, is using light to bend space and time. So could meta-materials be used to do the same thing?
     
  2. jcsd
  3. ZapperZ

    ZapperZ 30,158
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    You have quite a bit of misconception about the properties of metamaterials, and what this "cloaking" stuff is really about.

    Metameterials, as discovered by John Pendry, can produce one of 3 properties: negative permitivity, negative permeability, or a material exhibiting both properties at the same time. These are the materials can produce a negative index of refraction, materials with a photonic band gap, etc. These things are called metameterial because they are not really actual materials, but rather can be made up of conducting rods, split rings, etc.

    To equate the theoretically hypothesized "cloaking" as the ability to cause light to not escape is stretching it a bit. "cloaking" or making things invisible simply means that light that hits the material is bent around it and then continues on its way again as if the material isn't there. So there's nothing being absorbed and going round and round.

    http://physicsweb.org/articles/news/10/5/16

    We should always temper our enthusiasm on things like this before these things are actually verified experimentally. That is how physics works. Having seen these metamaterial research first hand, I can tell you that the fabrication of these materials are extremely difficult, and it has only a very limited bandwidth whereby these things are truly left-handed. Beyond that, these things behave like normal material. So this is still a new field, and many fundamental issues that still need to be resolved before we dream about the things you are talking about.

    Zz.
     
  4. Well thanks for the extra info, that website was really helpful.
     
  5. I also did some research on metamaterials. Zz mentioned their construction thru conducting rods, split rings, etc. I have found that these split ring resonators mentioned compose the unit cell of the lattice structure of the actual material that displays a negative index of refraction.

    Would you happen to know if metamaterials could be made with a different design for the unit cell?
     
  6. The short answer is yes. This is a very hot research topic and it turns out the SRR is not so convenient for scaling to shorter wavelengths. I don't have any links on hand, but for example a double-layer hole array has been explored.
     
  7. ZapperZ

    ZapperZ 30,158
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  8. I see from various publications that the two approaches to obtaining a negative refractive index is thru photonic crystals and the lattice structure method. The lattice sturcture requires unit cells of much smaller wavelength than the EM wave that is propagating. So the interest in new designs for a unit cell is in photonic crystals?

    Also, the terms left-handed material (LHM), negative index material (NIM), and metamaterial are one in the same, right?
     
  9. Both the photonic crystal and the "lattice structure" regimes have unit cells that can be engineered - they are both resonant structures. Typically for a NIM the unit cell of the lattice structure is smaller, but not much smaller than the wavelength, due to the need to maintain resonance. Since this is more challenging to construct one could argue that the cell design is more important.

    NIM & LHM are the same in this context, although LHM also applies to chiral (handed) structures so some prefer to avoid it. "Double-negative materials" is also used.

    Metamaterial strictly is a broader term where some property is manipulated by the structure... doesn't have to be negative index.
     
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