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Neodymium magnet partial shielding

  1. Apr 20, 2017 #1

    Martin Quevedo

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    Gold Member

    Hi all distinguished members of this forum !

    As my first post here I would like to open with a situation I have been struggling with
    I have attached a simple diagram of my problem

    I have 2 cylindrial N52 neodymium magnets axially aligned with each other with opposite poles facing each other.

    in the middle of both magnets there is a HiperCo 50 metal

    The idea is that the net force on each magnet is zero. That is, the force of repulsion between the magnets and the force of attraction between magnet and metal (hiperco alloy) cancel one another.

    I will very much appreciate if someone can share some math that allows to calculate the thickness required on the hiperco metal to achieve Fa and Fr to cancel.

    I have also attached BH graph of the hipeco alloy

    best regards,
    Martin magnet diagram.PNG hiperco1.PNG hiperco2.PNG
     
  2. jcsd
  3. Apr 23, 2017 #2
    Why don't you just test it physically? It's a lot more fun :-)

    This website might be what you need for looking up the maths and theory:
    http://www.physicspages.com/index-electrodynamics/
    http://www.physicspages.com/2013/07/16/diamagnetism/

    Magnets are dielectric with centripetal and centrifugal forces. They will exert that typical sideways pushing-away from each other if too close, which can be tricky to calculate. Hopefully you can try and make your "hovercraft" float with a far enough distance between the two magnets ;-) I suspect you need find a sweet spot (making the distance a harmonic of the wavelength maybe?).

    If the plate is much larger than the magnets's field size it might be difficult to keep it horizontal.
    I'm sure you already have this covered, but you will need something else to keep the plate stable until the forces settle and there is no more movement to induce new imbalance. Perhaps a simple tensegrity structure that will not restrict movement too much but stop the plate (and magnets?) from flying off. Just google it (or youtube).

    By the way there are a few "home-scientists" on youtube who have created very interesting videos showing what EM fields actually look like. This might help you to figure out if your calculations make sense.
     
    Last edited: Apr 23, 2017
  4. Apr 24, 2017 #3

    berkeman

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    If the plate is thick enough not to saturate, I don't think much of the field from one magnet will affect the other magnet. So the magnets will both stick to the sheet.

    If the sheet is very thin and can saturate, then I think the math gets pretty complicated, and you may just need to simulate the setup to get an idea of the behaviors.

    A better way to do this, IMO, is to cut a hole in the sheet between the magnets to let some field through so the magnets can influence each other. Experiment with the diameter of the hole versus the magnet diameters and spacings to see if you can arrive at a stable configuration...
     
    Last edited: Apr 24, 2017
  5. Apr 24, 2017 #4

    Martin Quevedo

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    Dear Karin,

    Thank you very much for your response!

    I am planning to do some tests on this particular situation
    I also wanted to know some math on the matter because I needed to at least get an approximate of the thickness of the hiperco 50 material to place between the magnets.

    All 3 components are fixed in space by mechanisms not shown in my picture.
     
  6. Apr 24, 2017 #5

    Martin Quevedo

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    Very interesting answer Beckerman!

    I was under the impression (wrong apparently) that a portion of magnetic field would go through depending on the thickness up to a saturation point. But according to what you described, it is a all or nothing situation. If no saturation accurs, all magnetic field will be re routed by the metal plate. and only if it saturates the remainng portion of the field would pass through.

    I am correct in the interpretation of your explanation?

    Best regards,
    Martin
     
  7. Apr 24, 2017 #6

    mfb

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    Staff: Mentor

    It is not "all or nothing", but if the plate is thick, the influence of the magnets on each other will be very small.
     
  8. Apr 24, 2017 #7

    Martin Quevedo

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    I was doing some simulation with QuickField. I used the BH curved provided by the manufacturer to configure the behaviour of permeability of the metal plate.
    In the simulation I was able to reduce the force to zero by varing the thickness of the plate. So, if the simulation is correct, this should mean that there is a portion of the field passing through the plate influencing the magnet on the other side.
    This would prove what you are stating here, mfb.
     
    Last edited by a moderator: Apr 24, 2017
  9. Apr 29, 2017 #8
    Sounds interesting. Let us know your results please, and your purpose :-)
     
  10. Apr 30, 2017 #9

    Martin Quevedo

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    I sure will
    I am working with the simulations but sometimes it is a bit hard to get the BH curve of the material
    Regards,
    Martin
     
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