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I B Field of Large Ring Magnet Calculation

  1. Aug 17, 2015 #1


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    Hi Everyone ,

    Can anyone explain why I am getting negative result with a large Neodymium N35 ring Magnet ?

    Br: Remanence field, independent of the magnet's geometry
    z: Distance from a pole face on the symmetry axis
    D: Thickness (or height) of the ring
    Ra: Outside radius of the ring
    Ri: Inside radius of the ring

    Br: 12,300
    z: 5mm
    D: 10mm
    Ra: 360mm
    Ri: 330mm


    I am getting a result of : -15.0893364057539 Gauss .

    Does it make sense for such a large magnet ?

    Thank you

  2. jcsd
  3. Aug 17, 2015 #2


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    Staff: Mentor

    Welcome to the PF.

    I'd suggest doing it with a calculator and writing down the value of each term individually. Then see if you can spot the error in your (Excel?) formula calculation above.
  4. Aug 17, 2015 #3


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    I did.

    The results are correct .

    Some said it is due to the fact that in the center of the ring there is very little field flux, which make sense . The center Z axis is very much away from the actual magnet.

    So far what I came up with is using a block magnet formula to calculate a ring magnet by converting it to liner from circular .

    But if there is a function for surface ring magnet strength. it would be very helpful.

    Thank you
  5. Feb 21, 2017 #4
    Hi, how did you get your value for z? I'm new to this and trying to work a similar problem, any help would be much appreciated
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