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Electromagnet pole design

  1. Jun 5, 2008 #1
    I'm attempting to get a rough estimate on how the shape of an electromagnet pole will affect the field produced. Most of the poles you see in labs are tapered, and not simply cylindrical - I'm wondering how this affects the field. After all, there has to be a reason why they would do such a thing.

    physically, I imagine that a very very narrow pole would have field lines concentrated strongly at the tip, giving a high B density but at the expense of uniformity. On the other side of the coin, a large flat cylinder will have field lines which are less dense, but more uniform.

    My understanding falters in the middle, with a "conical" shaped pole.

    If anyone can provide some insight i would be appreciative
  2. jcsd
  3. Jun 6, 2008 #2


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    Magnetic circuit design, with open poles, tends to be a black art.
    Less so for closed magnetic circuits.
    The rules for magnetic circuits are much like those for electric circuits.
    As I understand it, some of the recent software can do a fair job of modeling, but there are no closed form solutions due to somewhat ambiguous multiple leakage paths.

    My guess is that a larger core has less saturation, so tapering the core can reduce field leakage over the body of the coil, giving an effective increase in field strength at the pole.
  4. Jun 15, 2008 #3
    hmm. I thought I posted an analytic solutions, or sorts, here.
  5. Jun 15, 2008 #4


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    There were a bunch of these mag questions all at once, you posted to a lot of the other ones.
    I don't remember you posting to this one.

    I think there are commercial products that can get an iterative approximation to a question like this.
    If you have an analytic solution feel free to post it. :smile:
    AFAIK, there are only analytic solutions for closed magnetic circuits.
  6. Jun 15, 2008 #5
    Thanks, NT. Re:analytical; I think i've been abusing the language :redface:

    The magnetic field is had by summing over infintesimal dipoles, but which way do they all point? If I had to, i'd approach the problem like this: assuming no hysteresis, the minimum energy occurs when there's no torque on any dipole, so it may amount to finding the extremal in one variable, the energy. It's a two dimensional problem in r and z, with the diople magnitudes scaled by r.

    I'm actually more curious as to how this is normally calculated, then my own suppositions, so I wonder if this is the usual method.
  7. Jun 15, 2008 #6


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