Magnetic core with a coil

Case study: 2D magnetostatic with FEMM 4.2

By Dr Stan Zurek, August 2008

1. Menu > File > New

2. Magnetics problem > OK

3. Menu > Problem (see red rectangle)

4. Problem Type = Planar, Length Units = Millimeters, Freq = 0 (zero is required for magnetostatic solution), Depth = 16, Solver Precision = 1e-008, Min Angle = 30, Comment = (optional text here)

5. Menu > File > Save

6. Configure grid size = 2, and turn on “Snap to grid”

7.

8. Zoom in/out by clicking a few times and move the grid around if

necessary, the icons mean (from the top): zoom in once, zoom out once, autozoom, zoom by selecting/drawing a rectangle

9. Click to select “Operate on nodes”

10. Watching the status bar (at the bottom of the window) with X and Y

coordinates click to insert the following nodes (X, Y): (0, 0); (-2, 0); (2, 0); (34, 0); (-34, 0); (-42, 0); (42, 0); (72, 0); (76, 0); (-100, -100); (-100, 100); (150, 100); (150, -100)

11. If the node is placed in a wrong position use Menu > Edit > Undo, or select it with dashed rectangle (icon below Menu > Properties) and Delete (from keyboard or icon) – you can also select it by right click on it

12. Click to select “Operate on segments”, then click on a corner node to start

straight line and click again on a different node to finish a line. Click again on the same node to start another straight line, etc. Connect the corner nodes in a rectangle.

13. Click to select “Operate on arc segments”

14. Click on the nodes in the order shown below

15. Change angle to 180 degrees and click OK, an arc should appear as shown below

16. Repeat the procedure as to create the following structure (note, for the “upper” arc the node on the right should be clicked first and the finished on the left – the arcs are always drawn “counterclockwise”)

17. Menu > Properties > Materials Library

18. Drag-and-drop three materials: Air, Pure Iron and 2 mm Copper, click OK

19. Menu > Properties > Boundary > Add property

20. Name = “zero boundary” (can be any name), BC Type = Prescribed A, and all other parameters = 0, and click OK, and then OK again

21. Menu > Properties > Circuits > Add property, then: Name = coil plus, Circuit Current, Amps = 10, select “Series”

22. Repeat the steps above but use name “coil minus” and minus current “-10”

23. Click to select “Operate on block labels”

24. Use left button and click on the core, a new green node named <None> should appear

25. Right click on the name <None>, the node should change colour to red

26. Press Space and change the settings as follows

27. Click inside and also outside the toroid and set options for both as:

28. Switch off “Snap to grid”, click on the wire inside the toroid and set it as

(repeat the same for the outer wire, but choose “coil minus”):

29. At this point the model should look like this

30. Switch to “Operate on segments” (straight lines) and right click on the line

of the outer rectangle, which will turn red

31. Press Space, select “zero boundary” and click OK, repeat the procedure for

all the sides of the rectangle. 32. Menu > Mesh > Create Mesh (then accept with OK)

33. Menu > Analysis > Analyze (wait until the small window disappears) 34. Menu > Analysis > View results - a new tab will appear (see the red

rectangle at the bottom), the first tab contains the model, the second displays the calculated results, close the “FEMM Output window”

35. As default, the flux density |B| is displayed. The results can be zoomed in

the same was as described above for the model. The range of shaded graph can be changed by : Menu > View > Density plot, where also the plot can be changed to Field Intensity A/m

36. In the same way the Contour and Vector plots can be modified: Menu > View > Contour (or Vector)

37. The numerical values (at a given node, along a line, or over a surface) can be extracted by choosing the right option from Menu > Operation

38. To show and to export the numerical values along a given line go to: Menu > Operation > Contours 39. Switch on “Snap to grid” 40. Click on a point (-40, 0) and then (80, 0), a red line should appear

41. Menu > Plot X-Y, then choose |H| (Magnitude of field intensity) – if the “Write data to text file” is ticked, then the data will be exported to a text file. If the option is not selected then a graph is displayed (as shown below)