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litz skin effect and topological insulators

Discussion in 'Electronic Design' started by Jamie M, Nov 22, 2013.

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  1. Jamie M

    Jamie M Guest


    I was reading about topological insulators which can super-conduct
    electrons on their edges, I was thinking about this in relation to
    the high frequency skin effect. At a high enough frequency, the
    skin depth should be 1 atom deep on the conductor, and then the electron
    may have to travel on the "edge" only of the conductor, so
    there could be zero losses from resistance and supercondivity.

    The losses would be 100% from emission from the vibrating AC
    electrons. At an infinite frequency the vibration amplitude of
    the electrons would approach zero, and radiation losses would
    approach zero. Does this make sense that losses from skin effect
    could start to decrease or am I thinking about it completely backwards?!
    :) Would it be possible to approach a high enough
    frequency where the radiation losses could be recovered?

  2. Jamie M

    Jamie M Guest


    If you use two conductors separated by a thin insulator layer
    (nanometers) and run high frequency AC 180 degrees out of phase in
    them, will the radiated losses cancel out? If so then at high enough
    frequency maybe that could be a superconductor.

  3. RobertMacy

    RobertMacy Guest

    No. The skin effect you describe requires the current down inside to force
    the current to the outside and the current down inside will eat power.

    To test your idea, use free simulation tool, femm 4.2, and try it out,
    you'll better understand where skin effect comes from. And learn a lot
    about magnetics.
  4. Guest

    The possessive form of boss is boss'. When the last letter is an 's'
    or a 'z', whether it's plural or not, the possessive form has a
    trailing apostrophe and no additional 's'.
  5. Jamie M

    Jamie M Guest


    Thanks I checked wiki:

    The current down inside that forces the current to the outside, is the
    AC induced eddy currents, and these eddy currents also move towards the
    skin at higher frequency, so at some high enough frequency even the
    eddy currents approach the outer layer of atoms on the conductor. Not
    sure what would happen in this case, but probably the AC eddy currents
    would create a plasma discharge or something off the surface?!

  6. RobertMacy

    RobertMacy Guest

    I thought about that just after posting. Should check using FEA and a
    model with a VERY thin surface layer of almost infinite conductivity and
    see what happens. Something must not work here, else a single layer of
    superconductivity would ALWAYS steal all the carriers so is not an easy
    thing to even understand.
  7. Guest

    Current does flow on the surfaces in superconductors, even at DC.
    The current layer has finite thickness, however, it's called the
    London penetration depth.

    The current tries to distribute itself across the cross-section
    of the wire such that the stored energy is minimized. Each current
    filament can lower its energy by moving away from other filaments.
    One would then expect that all the filaments would move as far away
    from each other as they can, i.e. to the surface of the conductor.

    Anyway, there is only a finite density of superconducting charge
    carriers available in a material. The smaller fraction of the
    cross-sectional area the current filaments occupy, the smaller
    number of carriers must carry the current, and the faster each
    carrier has to move. Because the carriers have mass, there is
    kinetic energy stored in their motion. This kinetic energy storage
    looks to the driving electric circuit exactly like inductance,
    hence it's called "kinetic inductance". However, the energy is stored
    as kinetic energy, not in the magnetic field. Therefore the kinetic
    inductance does not couple magnetically to other nearby inductors,

    So, there is a tendency of the current filaments to move farther
    from each other, and thus reduce the stored magnetic energy. But
    by doing so they induce a larger and larger kinetic energy storage
    when the current gets packed to the surfaces. The two effects
    balance when the current distribution reaches (in the case of an
    infinite slab geometry IIRC) and exponentially decaying shape,
    with decay length equaling the London penetration depth. For our
    Nb thin films at LHe temperature this is roughly 90 nm.

  8. Guest

    If there are standards on every side of the argument, it sounds like a
    "real writer" can do it any way sheit pleases. "That's the nice thing
    about standards..."
  9. Jamie M

    Jamie M Guest


    I think a microwave waveguide is acting kind of like a topological
    insulator too, the microwaves reflect off the surface and don't
    penetrate, but still there is some interaction with the surface
    atoms that is near superconducting type.

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