Guidelines for Mesh Connectivity

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.