Domain Connectivity for Unconnected Meshes in Altair Feko
Altair EmployeeClassical MoM-based Methods in Computational Electromagnetics Simulation use a mesh discretization with triangle elements on surface structures. Each triangle represents basis functions to describe the current distribution on the surface. The Rao–Wilton–Glisson (RWG) basis functions (named after their inventors) are typically used to enforce the current continuity across junctions between patches [1]. Therefore, it is important to create clean simulation meshes with well-connected triangles elements having common vertices and edges.
Recently Altair Feko [2] introduced a new Domain Connectivity Method, that can tread unconnected meshes as if they would be connected. Domain Connectivity is available since Feko 2022.3 (with setup in EDITFEKO) and was integrated in the CADFEKO GUI in version 2023. The technology behind this approach is the so-called Discontinuous Galerkin Domain Decomposition Method. The elements along the open edge are treated with special types of basis-functions with additional penalty terms. For more details about such concepts see [3] and [4].
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.
The next Figure 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?
Next picture 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. 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 the next figure 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 CADFEKO?
The Domain Connectivity setting can be defined since version 2023 in CADFEKO (in the previous version the feature was only available in EDITFEKO):
- Assembly the model as usual in CADFEKO and define all settings and requests
- Go to Solve/Run tab and select “Domain Connectivity”
- Select pairs of faces in the Create Domain Connectivity window
- Define tolerance, to specify maximum distance range between two edges
- Feko will automatically identify open edges on both faces whose distance is smaller than the defined tolerance
The corresponding edges, that are treated with Domain Connectivity, can be visualized in POSTFEKO for verification.
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, LE-PO, RL-GO and UTD
The complete workflow and all relevant information about the Domain Connectivity feature in Altair Feko is summarized in a nice video [5] on the Altair How-To Youtube channel. To test the method yourself, you are welcome to download the attached drone model.
References:
[1] S. M. Rao, D. R. Wilton, and A. W. Glisson, “Electromagnetic scattering by surfaces of arbitrary shape,” IEEE Trans. Antennas Propag., vol. 30, no. 3, pp. 409–418, May 1982, doi: 10.1109/TAP.1982.1142818.[2][3] M. A. Echeverri Bautista, F. Vipiana, M.A. Francavilla, J. Tobon: A Nonconformal Domain Decomposition Scheme for the Analysis of Multiscale Structures, IEEE Trans. Antennas Propag., vol. 63, no. 8, August 2015.
[4] Z. Peng, K. H. Lim, and J. F. Lee: A discontinuous Galerkin surface integral equation method for electromagnetic wave scattering from nonpenetrable targets, IEEE Trans. Antennas Propag., vol. 61, no. 7,pp. 3617–3628, July 2013.
[5] Webinar at Altair How-To Youtube channel: Domain Connectivity feature in Feko (youtube.com)