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Shielding a magnetic field

  1. Sep 25, 2012 #1
    Hi everyone,

    I have two questions related to magnetic fields.

    Firstly, if I have two bar magnets with opposite poles facing each other, ie NS - NS, how do I measure the magnetic field strength at any point between the two magnets?

    Secondly, how would I shield the magnetic fields of the bar magnets in a box so they are not detectable outside?

    Any help would be appreciated, thanks.
  2. jcsd
  3. Sep 25, 2012 #2
    Better way to prevent all the magnetic field lines from coming outside of the box is, use a box made up of a super conductor to separate bar magnets. The super conductor plate is able to divert all the field lines.
  4. Sep 25, 2012 #3
    Use a "Hall Probe" (http://en.wikipedia.org/wiki/Hall_effect_sensor) to measure the magnetic field from the Bar Magnet.

    To shield the magnetic field , you could use an iron box to enclose the bar magnets .
    (or a thin layer of iron foil would also suffice)
  5. Sep 25, 2012 #4
    hi.hms.tech I dont think a iron box can separate magnetic field lines. I have doubt about it. Can you explain?
  6. Sep 25, 2012 #5
    Thank you for your replies.

    That sounds useful, though unfortunately I'm restricted in terms of power supply in this setup, so I need to go with the most energy efficient option and avoid a current conductor of any sort if possible.

    The Hall probe will be useful for measuring, though what I should have written was how do I calculate the field?

    Also for the iron box shielding, how do I calculate the change in field strength across the shielding?

    Thanks again.
  7. Sep 25, 2012 #6


    User Avatar

    Staff: Mentor

    Check out the FAQs section of Magnetic Shield Corporation's website:


    They mostly sell netic and conetic magnetic shield material and shapes, but the concepts would apply to iron shielding as well.
  8. Sep 25, 2012 #7
    Thanks for that - that will be useful.
    However, if I have a shield at a distance from a magnet, how do I calculate the field at that distance?
    In a related question, if I have two magnets, how do I calculate the field strength at any point between them - is it merely by superposition or are there other parameters to take into account?
  9. Sep 26, 2012 #8
    I would look into an advanced electrodynamics textbook, there are closed form solutions for what you need, although they will be very very complicated and require a far field approximation.
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