Meshing guidelines are given to ensure electrical connectivity in the
mesh.
Elements must be connected at edges or vertices to ensure electrical connectivity. Most
of these rules are automatically complied with when creating Feko
models in CADFEKO. However, adherence to these rules should be
maintained when combining CADFEKO models with EDITFEKO scripting (for example attaching an antenna modelled
with geometry cards on an aircraft meshed in CADFEKO), or when
creating the geometry only in EDITFEKO, or when working with
imported meshes.
Note: Cuboidal volume elements used to model volume dielectrics (with the DK, DZ and QU
cards), do not need to be connected in this manner.
When creating structures with scripting commands, wires are divided into segments that
are equal to or shorter than the specified segment length. For surfaces the triangle
edges along the boundary of the surface are always equal to or shorter than the
specified edge length. Therefore, meshing the same line with the same mesh size will
always give the same number of divisions of equal length. The internal edges may,
however, be longer than the specified edge length. This is not necessarily the case with
CADFEKO meshes where the specified mesh size is the average
size and the internal structure influences the placement of vertices along the surface
boundaries.
When creating wire junctions as shown in the figure below, it is important to ensure that
the wire AB have a vertex at point C. The best option is to construct this as two wires,
one from A to C and the other from C to B.
Figure 1. Example of a wire structure.
Similarly, where two surfaces touch, the common edge must be part of both surfaces. For
example, the surface in the figure below should not be created as two rectangles ABFG
and CDEF. If done in this manner, it is highly unlikely that there will be an ohmic
connection along the line BF. There are a number of ways to correctly create this
structure. It can be created from the rectangles ABFG, CDHB and BHEF or the quadrangles
ABEG and BCDE. In both cases the contacting edges are common and will be meshed
correctly. The simplest way to mesh this structure is to create a single polygon
ABCD(H)E(F)G.
Figure 2. Example of a wire structure.
A connection point between a segment and one or more triangles is only recognised when
the beginning or the end of the segment is coincident with the vertex or vertices of the
triangles. In the figure below an incorrect connection is depicted on the left and a
correct connection on the right (where the segment is connected to six triangles).
Figure 3. Incorrect (left) and correct (right) connection between a segment and
triangles.
When curved structures (such as circles, cylinders, spheres and so forth) are modelled, a
finer mesh may be used along the curved edges to get a more accurate representation of
the geometry. In this case the same edge length should be used on both edges and the
reference points should be identical as depicted in the figure below.
Figure 4. Incorrect (left) and correct (right) connection between a segment and
triangles.
