Finite Element Method Magnetics : Miscellaneous

Notes on Incremental AC Magnetics Problems

Improvised Asymptotic Boundary Conditions

...are another way of approaching Open Boundary problems. This page presents values necessary to implement really high-order IABCs.

Mathics is a Computer Algebra System that uses Mathematica-like syntax. A Windows installer is now available.

Improved Convergence
In a recent conference presentation, the convergence of FEMM was compared to several other programs, including several solvers with various sorts of adaptive mesh refinement. Some recent changes have been made to improve the convergence of FEMM by changes to the meshing. While the program does not use adaptive meshing, several heuristics have been added to the mesh generation. These changes result in convergence that is similar to programs with adaptive meshing on 1st order triangular elements. This note compares the performance of the scheme to various adaptive solvers on a specific electrostatic benchmark problem.

FEMTEC 2011 Presentations
Improved Continuum Skin/Prox Model
FEMM Overview

C# Connection Example
An example of how one might go about connecting to FEMM as an out-of-proc ActiveX server from a client written in C#.

Stacking Factor

A parameter that FEMM requests as part of the definition of a laminated material is the lamination fill factor or "stacking factor". This note aggregates guidance for selecting the stacking factor depending upon lamination thickness.

Soft Magnetic Materials

FEMM users have expressed an interest for BH curves that are defined up to very high levels of saturation and come from a well-documented source. This note discusses materials described in the Metals Handbook, 8th ed, Vol. 1 that are now included in the standard FEMM magnetic materials library. This source presents BH curves for a wide range of materials up at field intensities up to about 300,000 A/m. Electrical conductivities for these materials (along with the sources for the values) are also tabulated.

Excel Connection Example

A very simple example of how one might go about connecting an Excel spreadsheet to FEMM using ActiveX.

Mechanical and Electrostatic Analogies to Permanent Magnets

For the purposes of developing an intuitive feel for the fashion in which energy is stored in a permanent magnet and its environment, it is useful to use analogies to other types of physical consideration. In this note, the magnetic circuit representation of a magnet driving an external reluctance will be reviewed. Then, capacitive and mechanical analogies to a permanent magnet will be considered. These analogies have an equivalent circuit representation that is identical to the one used to describe a permanent magnet.

Analysis of a Cylindrical Permanent Magnet

Magnetic circuit representation of a PM cylinder including expressions for stored energy, coenergy, and magnetometric demagnetization factor

Magnetic Circuit Derivation of Energy Stored in a Permanent Magnet

A note that considers an intuitive approach to computing the energy stored in permanent magnets based on the magnetic circuit representation of a permanent magnet.

Wire Size Worksheet

A fairly widely used analytical formula for the diameter of bare wire as a function of AWG wire gauge is:

dwire = (0.324861*inch)*exp(-0.115943*AWG)

A Mathcad worksheet that implements this function (and a few other functions related to wire resistance and weight calculation) is linked below.


Lua is distributed with double precision numbers as the standard number type. However, for many scientific applications (e.g. FEMM), it would be nice to have complex numbers as the standard number type. ComplexLua is a project in which Lua 4.0 has been recompiled in C++ using the complex number class from FEMM as its standard number type. There is also a dialog-based interpreter program that demonstrates the use of ComplexLua embedded inside another program. A more detailed description of ComplexLua is available, along with the ComplexLua source distribution (compiles with MSVC++ 6 or later).

Force on NdFeB Disc Magnets Including Eddy Current Effects

A note that examines the effect of eddy current effect in thin disks of NdFeB.

  Attachment Size Date Added   9.56 KB   3/20/2015 1:34 pm
      FEMM_Presentation.pdf   963.89 KB   11/17/2015 8:53 am