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Insulation of magnetic field.

  1. Mar 14, 2004 #1
    !!! ATENTION HERE !!! Insulation of magnetic field.

    [?] I don't know much about what I am about to ask on this forum (isn't it what this is all about?!)... My question is about MAGNETISM(I was hoping that this is the easiest way to get the answer from someone who feels her/himself competent).

    QUESTION: Is it somehow possible to insulate a magnetic field of a natural magnet so that field spreads only in desired direction?

    (is there some material that "soaks" the magnetic field so that it doesn't spread beyond it? I know that most materials don't do that.)
    (what is 'the problem' regarding that question?)
  2. jcsd
  3. Mar 14, 2004 #2
    Well, at least plasma interacts with magnetic field so that it could be used for insulating areas from a magnetic field. If there is no magnetic field originally inside the plasma, it pushes all incoming magnetic field lines aside.
  4. Mar 14, 2004 #3

    But what I had in mind is something that could be explained with an exempe: imagine that you have a natural magnet "wraped" (if you excuse the expresion) in something, and magnetic surface below; now you move the "wrapped magnet" from free area to area exactly above the magnetic surface - the main thing: when you move "wrapped magnet" TOWARD magnetic surface (closing-up on it) you don't feel force, only when you place the "wrapped magnet" directly above the magnetic surface (90 degrees - or point it towards) - then you feel the force...

    (you are suggesting that only plasma can do something with magnetic field, but is it possible to (somehow) make this effect)

    (actualy (:to extremely simplify it) it can be compared to effect of watterhose... the jet is directed onto a point)
    (as I understand: you are saying that it isn't possible)
  5. Mar 15, 2004 #4
    Hmm..I see what mean. Magnetic field lines have such a property that they always form closed loops. So what you want is a bar magnet with field lines emerging from one end and no existing elsewhere near the magnet. I'd pretty sure this can't be done. The field lines must go to the other pole of the bar magnet. It means that even if the bar magnet would wrapped inside some new revolutionary diamagnetic material that makes almost makes the field vanish, it would vanish everywhere.

    So, no, it can't be done, I'm afraid. It is impossible because of properties of the magnetic field lines. Please someone correct me if I'm wrong, though...
  6. Mar 15, 2004 #5

    Chi Meson

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    Re: !!! ATENTION HERE !!! Insulation of magnetic field.

    Actually, yes. Magnetic field lines (or "flux") can be channeled by ferromagnetic materials. Specifically, if you enclosed a bar magnet in a taurus (donut shaped thing) made of soft iron (very pure iron), the magnetic field lines would almost entirely be contained within the iron taurus. THis is regularly done with transformers which change the voltage of ac electricity.

    "almost entirely" is of course added in becuase nothing is perfect or pure and some magnetic field cound be detected outside the iron taurus, but it would be much less than without it.
  7. Mar 16, 2004 #6
    Yes, well; I started this theme without seriously considering anything (I started from what I want to achive; not - how to achive it). Of course we all know that magnetic field lines form a loop (encircle the source of the field), but - isn't it possible to (somehow) "squeeze" those field lines - imagine a drawing of a circle and a circle within that circle; diametar of the inner circle is 'a lot of' times greater then distance between two circles - now: the inner circle is magnet (the base of the bar), and the outer one is (supposed) material that affects the field and "squeezes" it - so it doesn't spread all-around, but go thorough space inbetween - of course lines must be closed, but (question:) would this create an effect that I explained earlier?
  8. Mar 16, 2004 #7
    Re: Re: !!! ATENTION HERE !!! Insulation of magnetic field.

    *Wouldn't pure iron be magnetized (not permanently of course)? (induction? explain more about what you said)
    *Does that weaken the magnetic field (or just (actualy) channels it as you said)?
    *What is your comment on my previous reply (to Sickboy)? How does it fit in what you said?
    *What about superconductors freezed with liquid nitrogen - can they be used to perform this "trick"?
    (actualy: how does all that work? Supperconductor is floating - it doesn't "try to escape", and when you press it you can lift the freezed part bellow - it's like it tries to preserve the present position and state... what is the mechanism involved in that)
  9. Mar 16, 2004 #8
    "it pushes all incoming magnetic field lines aside" - what do you mean by that(?) - explain it on an example: imagine that plasma is (somehow) a torus around the magnet bar.
    Last edited: Mar 18, 2004
  10. Mar 16, 2004 #9
    Re: !!! ATENTION HERE !!! Insulation of magnetic field.

    I read a science fiction story once, and it talked of fermionic matter. Apparently, it is matter where the orbits of electrons have collapsed, and make chemistry impossible. It stated that it would make excellent hull material, but a new purpose could rise from it: When there are no electromagnetic particles to interact with in the fermionic matter, perhaps it appears reflective to the electrons from the magnet themselves. Either that, or the fermionic material would be absolutely transparent to said EM particles. Just a thought.

  11. Mar 16, 2004 #10

    Chi Meson

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    Yes the iron would be magnetized, but the magnetic field lines would be entirely contained within the taurus. Now, you would be enclosing the bar magnet into one side of the donut, not "in the hole."

    The magnetic field would actually be strengthened since the bar magnet would allign the domains of the soft iron of the taurus, but again, there would be near zero net field outside the taurus as long as it is unbroken.

    As to your comment, I think it is a little confusing. Magnetic field lines do not circle their "source" unless you are talking about a straight current-carrying wire. Field lines do not circle a bar magnet, they go through the magnet. I really don't follow the rest of what you are describing. Perhaps make a jpeg or gif image?

    When a magnetic field approaches a superconductor it creates a current in the superconductor. THis current goes around in circles and creates another magnetic field that counters the original magnetic field. No satisfactory explanation can be made in one paragraph.
  12. Mar 16, 2004 #11


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    Ummm. A taurus is a bull. THe word for donut shape is torus. Anyway, the image of using bulls to shield magnetic fields gave me a good chuckle.
  13. Mar 17, 2004 #12

    Chi Meson

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    No, I DID mean "a donut-shaped bull made of iron." Sheesh!
  14. Mar 17, 2004 #13
    At work we use Mu-Metal shielding to contain magnetic fields. Maybe you could shape the mu-metal in a way to acheive your goals.

    We also use and make scanning electron microscopes which use an electromagnetic final lens for focusing the e-beam. The degsign of the lens focuses most of the field strength into a small area but there is still some leakage around the lens. The lens is made from two soft iron cones which sandwich a coil of copper wire. By changing the dimentions of the two cones we can get some very interesting field line patterns.
  15. Mar 18, 2004 #14
    (to Chi Meson and any other...)
    1.) About confusing part: I just wanted to say that I agree with you - I didn't bother very much to explain what I meant with what I said - as we all know how lines of magnetic field look like... (I tried to agree using just one sentence...) (obviously I didn't use the best words to describe it) (...) I understand what confused you: when I said that lines of magnetic field encircle the source of magnetic field I just tried to desctibe (CONFIRM!) how ALL THE FIELD LINES (of natural magnet) go from one pole to another - every one of them encircleing the magnet by GOING AROUND AND THOROUGH IT, and all of them enclosing the magnet...
    All of what I am saying about has nothing to do with electricity - thus neither with wire and its field when you let the electric current thorough it.
    2.) That sentence confused you so you didn't understand the rest of what I was saying. Read it again - better yet draw it having in mind that inner circle is a cross-section of a natural magnet (shaped into cylinder)... The outer circle is torus of material that is to "squeeze" (or something...) field lines thorough space between magnet and torus - you gave me an answer: soft iron does the trick.

    *the next page*
    Last edited: Mar 21, 2004
  16. Mar 18, 2004 #15

    Chi Meson

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    OK. All clear. I'm pondering your scenario. I do not think "squeeze" is the operative word here, but... if anyone else wnats to take this...g'head.
  17. Mar 18, 2004 #16
    (to Chi Meson)

    So (to conclude) - you are saying that torus made of soft iron would prevent the field to spread around (...but not entirely...) and enhance the field only in front of the hole of torus.

    ...Actualy (like I said it second time I wrote) the MAIN thing that I want to achive is to insulate magnet so you don't feel the force when approaching the magnet below by moving it horizontaly toward (you're moving the insulated one (above)), but only when you place it DIRECTLY above...
    What would be the scenario if the soft iron torus is that isolation for magnet bar above?
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