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Help with linear motor, magnetization?

  1. Jul 10, 2014 #1
    Hello, attached is a picture of a cylinder magnet moving in and out of a coil, in a linear AC generator configuration.
    Below it, there are 3 possible configurations for the magnetization of the magnet (axially/diametrically/radially).
    Which of the 3 configurations will produce more voltage on the coil, assuming same motion, magnet mass and magnet strength conditions for all three of them?
     

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    Last edited: Jul 10, 2014
  2. jcsd
  3. Jul 11, 2014 #2

    Baluncore

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    The missing fourth way is best.
    The second and third will not produce much voltage at all since the field is perpendicular to the coil axis.
    The first, axial, will produce a small second harmonic voltage due to divergence of the field at each end of the magnet.

    In order to generate a significant voltage you must reverse the magnetic flux through the coil.
    A fourth way uses a magnet with NS-SN-NS, which will reverse the field four times per pass.
    The distance between the magnet poles should be greater than the axial length of the coil.
     
  4. Jul 11, 2014 #3
    Ok so basically you mean like the attached picture?
    I am a bit confused. Which of the three you mean?

    1. The distance between the individual magnets to be greater than the length of the coil, and all 3 magnets to be moved at the same time back and forth?

    2. Or each individual magnet length (magnet cylinder length) to be greater than the length of the coil?

    3. Or the three magnets to be forced to touch each other and the total composite magnet length to be greater than the length of the coil?
     

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    Last edited: Jul 11, 2014
  5. Jul 11, 2014 #4

    Baluncore

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    Yes, like your diagrams. But again, the missing fourth way.
    4. The three magnets to be forced to be close to each other,
    and each individual magnet length (magnet cylinder length) to be greater than the length of the coil,
    and all 3 magnets to be moved at the same time back and forth.

    There is no advantage to be gained from having two different poles within the coil at the same time as their fields would partially cancel. The length of a magnet is the distance between the poles, so the coil should be shorter than the magnet. The distance between the similar poles can be considered separately. I would make the magnets as close as convenient so the N SS NN S pole pitches were similar, but without too much repulsion.
    Draw arrows on your field lines and you will see better how it works.
     
  6. Jul 11, 2014 #5
    Thank you this has been very helpfull.
    The last picture in this page https://www.kjmagnetics.com/magneticfield.asp shows a simulation of two magnets repelling and forced to come close. This shows the the closer they come the better, maybe I should try touch the magnets...
     
  7. Jul 11, 2014 #6

    Baluncore

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    But notice that, as the repelling poles get closer, the field gets closer to the magnets, so the coil outside diameter needs to be as small as possible to be cut by the maximum flux.
     
  8. Jul 11, 2014 #7
    That seems trully correct! Thanks a lot!
     
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