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Magnetic field of a solenoid

Discussion in 'Electronic Design' started by John Woodgate, Nov 30, 2003.

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  1. I'm afraid this article isn't about gun ownership or Presidents. Not
    even coil guns, feedback or abduction. Sorry.

    Does anyone know where I can find an analytic expression for the
    magnetic field vector (or preferably its paraxial and radial components)
    at an arbitrary point *outside* a cylindrical solenoid?

    Plenty of web sites give the field at the centre and some give it at one
    end, but outside? Nah. One would think that the external field was never
    of any consequence.

    I'm going to be off-line for a while, but would appreciate a timely
    response. TIA.
     
  2. You can calculate the field caused by a current through
    a wire segment ? I don't have the formular at hand but
    could look it up if required. The direction of the field
    is perpendicular to the current vector and perpendicular
    to the distance vector. Something proportional to i/r.
    Then do the vector integral by adding vectorially the
    components of each wiresegment.

    Rene
     
  3. I think you have to integrate the field from a current loop over the
    dimensions of your solenoid for each point in the space around the
    solenoid.

    http://www.netdenizen.com/emagnet/offaxis/iloopoffaxis.htm
     
  4. I read in sci.electronics.design that Rene Tschaggelar <>
    Yes, I know that's how to do it, but I have at present a failure to
    visualise the geometry, even with a wire model I just made. I can only
    do that sort of mathematics when the wind is nor-nor-west by south. (;-)
     
  5. How about doing the display for the projections or components ?

    Rene
     
  6. Fred Bloggs

    Fred Bloggs Guest

    There are freeware downloads for Finite Element Analysis specifically to
    solve magnetics problems. QuickField is one, specifically has an example
    for calculating solenoid force as a function of geometry and magnetic
    properties of the coil-close- at least involves a solenoid-) It is a 3M
    byte download-free and works-by Tera Analysis.
     
  7. James Meyer

    James Meyer Guest

    I was prepared to suggest that one myself. QuickField also does
    electrostatic analysis IIRC. All in all, a very handy program much like SPICE
    for doing "what if?" simulations.

    Jim
     
  8. I read in sci.electronics.design that Fred Bloggs <>
    To do what I need to do, I need an analytic expression: a FEA won't do.
    I had a DOS version of Quickfield, but I couldn't even understand the
    manual. (8-(
     
  9. Hello John P.,
    this is a great link about the formulas for a one turn coil.
    There is also a link to a sample source code (C-program) within this page.
    http://www.netdenizen.com/emagnet/offaxis/elliptic_c.htm
    This program calculates the off axis field for a one turn coil.
    The only addon needed is to program the sum of the H-fields over all turns.
    I have done it as an exercise based on this program from E. Dennison (Nov
    17, 1998).



    Hello John W.,
    sorry that there is no single formula.
    Please let me know if you are interested in the source or the .exe program.
    The program have to be additionally extended if the coil has more than
    one layer of windings. But this is an easy task.
    Can you give me some idea about the properties of your coil?

    Best Regards
    Helmut
     
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