FEMM Manual - Finite Element Method Magnetics

Figure 2.22: When in doubt plots and integrals taken on this side of a contour.
2.3.10 Line Integrals
Once a contour has been specified in Contours mode, Line Integrals can be performed along the
specified contour. These integrals are performed by evaluating a large number of points at evenly
spaced along the contour and integrating using a simple trapezoidal-type integration scheme.
To perform an integration, press the “integral” icon on the toolbar (as shown in Figure 2.20).
A small dialog will appear with a drop list. Choose the desired integral from the drop list and
press OK. The amount of time required to perform the integral will be virtually instantaneous for
some types of integrals; however, some types may require several seconds to evaluate. When the
evaluation of the integral is completed, the answer appears on the screen in a pop-up box.
One “tip” that may aid with the definition of contours of integration is that a curved integration
contour can be defined in a fairly painless fashion by hitting the Shift key. Hitting the Shift key
tells the program to turn the last segment in the defined integration contour into an arc segment. A
dialog then pops up that prompts for the desired attributes of the arc.
The line integrals currently supported are:
• B.n. This integral returns the total flux passing normal to the contour. This integral is useful
for determining the total flux in a bulk flux path. This result might then be compared to
predictions from a simpler magnetic circuit model, for example.
• H.t. The integral of the tangential field intensity along the contour yields the magnetomotive
force drop between the endpoints of the contour. Again, this integral is useful for comparison
to or validation of magnetic circuit models.
• Contour Length. This integral returns the length of the defined contour in meters.
40