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Focussed electric field

  1. Nov 13, 2008 #1
    I have been trying to think of some way to concentrate an electric field, locally on a given electrode. It is possible by using a very sharp tip on the opposite one, but is it possible by any other means such as an external magnetic field or by introducing different materials within the two electrodes.
  2. jcsd
  3. Nov 13, 2008 #2
    A source at one focus of an ellipsoidal reflective surface will focus the radiated energy at the other focus.


  4. Nov 14, 2008 #3
    Thanks a lot for your reply...I am bit new to electromagnetism...so could you point me to some books or websites where I could find some more information.

    When you talk of a source, do you mean a source of electromagnetic waves? and is the ellipsoidal reflective surface similar to that of a dish antenna that we commonly see.


  5. Nov 14, 2008 #4


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    Although I'm not sure, I think that Bill is referring to the type of reflector used in some laser cavities. It looks something like a standard car muffler (cross-section is similar to a medicine capsule). Each of the curved surfaces has its own focal distance, so something that occurs at one is focused on the other. In a laser, for instance, you would have a xenon flash tube lying along one focal plane and your lasing medium rod along the other. When the tube fires, the light is focused on the rod to begin pumping.
  6. Nov 14, 2008 #5
    I guess what you are talking about is something similar to an optical lens. However, if I have to concentrate the electric field, the equations will be completely different. Will an optical lens ever focus an electric field?
  7. Nov 14, 2008 #6


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    No, it's not a lens; it's a reflector.
    An optical lens will not focus an electric field. It will focus electromagnetism, since that's what light is. In any event, a lens is not what Bill meant.
    This is really not one of my specialties, so I'll refrain from further comment. Bill or someone else will have to carry this on.
  8. Nov 14, 2008 #7
    Look for info on "gregorian antenna". A gregorian antenna uses an ellipsoidal subreflector to feed a parabolic main reflector (the ellipsoid and parabola have a focal point in common).


  9. Nov 14, 2008 #8


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    It sounds like thinktank wants to focus an electrostatic field. A reflecting surface as used for optical-frequency electromagnetic waves will not do this.

    The only way I can think of to do this is to have a sharp tip on the electrode where you want the field to be high. Sharpening the opposite electrode would actually weaken the field where you want it strengthened.
  10. Nov 14, 2008 #9
    If so, that would be a different problem.

    Perhaps a hemisphere of pointy electrodes (directed inward) would work in a similar fashion - with the center of the sphere as the "focus" of the static field.


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