This article describes workflows and conditions for the new Domain Connectivity feature in Feko 2022.3. With this new approach unconnected meshes can be treated in Feko simulations as if they would be connected.
New Feature in Feko 2022.3: Domain Connectivity for Unconnected Meshes
With the newest Feko release 2022.3 a new Domain Connectivity Method is introduced. With this new approach unconnected meshes can be treated as if they would be connected. The technology behind this approach is the so-called Discontinuous Galerkin Domain Decomposition Method.
What are typical application cases for Domain Connectivity?
For complex real-world problems, the simulation model is frequently assembled from different parts coming from different sources. For antenna integration scenarios large structures – like vehicles or aircrafts – are usually preprocessed for CAD cleaning, midsurface creation, model assembly and meshing in specialized tools like Altair HyperWorks. These prepared meshes can be easily imported into CADFEKO.
On the other hand, one would like to use fully parameterized geometric models for antenna optimization in the larger scenario. The new domain connectivity approach allows to connect the static mesh and the dynamic parameterized geometry without having to take care of the usual required node connectivity.
Figure 1 shows such an example: The orange marked antenna region is built in CADFEKO with parametrized geometry and the mesh will be automatically adapted to different parametrizations. The outer part is an imported mesh.
What kind of meshes can be treated with Domain Connectivity?
Figure 2 show the different mesh scenarios for this connectivity use case. The left picture shows the classical node connection, which ensures that the current distribution along the common edge is calculated correctly. On the right side the nodes of the two parts are not connected and the gap defined by this will change the current distribution and thus the antenna characteristics of the nearby placed inverted-F antenna.
The domain connectivity can be applied for those unconnected meshes, if the gap is small regarding the wavelength lambda. For high accuracy the gap distance g should be chosen as g = lambda / 1000. E.g. for a FM band investigation up to 110 MHz g should be not larger as 2.7 mm and for LTE simulation up to 2.7 GHz g should be around 0.1 mm. With greater distance, the result becomes less accurate and margins g > lambda /100 should be avoided.
In Figure 3 the current distribution for 3 different mesh connections is plotted:
- the connected mesh is used as reference simulation
- the unconnected mesh with domain connectivity shows the same current distribution as the reference
- the unconnected mesh without domain connectivity shows a different current distribution. The vector direction indicates that the currents do not flow across the gap but parallel to it.
How is the Domain Connectivity defined in EDITFEKO?
The domain connectivity is added in Feko version 2022.3 and can be defined in EDITFEKO using the DC-card with the following workflow:
- Assemble the model as usual in CADFEKO and define all settings and requests
- The pre-file is automatically generated from CADFEKO
- Open the prefile and click at the Solve/Run tab
- Define Domain Connectivity with the DC-Card:
- Set number of connections
- Define for each connection the labels of the corresponding faces
- Define for each connection a tolerance distance, in order to distinguish between regions, where a gap in the model is desired resp. not desired.
- Run prefeko to create the fek-file for the simulation
To identify the correct label names, it is recommended to change in POSTFEKO the mesh color to “Element label” (under the mesh tab) and activate “Mesh display” (under the display tab). In this example the geometric face “Union2.Face2_2” is connected with Domain Connectivity to three different mesh faces.
Results
The example represents an inverted-F antenna in the Bluetooth frequency band at 2.45 GHz. To validate the results for the antenna gain, the three connectivity configurations are simulated:
- The blue curve shows gain pattern for the reference (connected mesh)
- The red curve shows the gain for the disconnected case
- The green dotted curve shows the gain for the disconnected case with domain connectivity and is identical to the reference curve.
Requirements for Domain Connectivity
The following boundary conditions for the application of the method have to be considered:
- Gap distance g should be about lambda / 1000 and must not be greater that lambda / 100.
- Both meshes must not penetrate each other.
- The domain connectivity edges must not be part of a dielectric region. However, dielectrics can be defined elsewhere in the model.
- For T-junctions the domain connectivity cut must not be through the junction.
- Domain connectivity can be applied for MoM and MLFMM, but not for asymptotic methods like PO, LEPO, RLGO and UTD