The Electromagnetic Waves, FEM-BEM Interface
The Electromagnetic Waves, FEM-BEM interface () allows to build hybrid FEM-BEM models, where the boundary element method (BEM) is used to compute the electric fields outside the finite element method (FEM) domains. This multiphysics interface adds an Electromagnetic Waves, Frequency Domain interface and an Electromagnetic Waves, Boundary Elements interface. The multiphysics coupling assures continuity of the tangential electric fields across boundaries between the two interfaces.
Frequency-domain and Wavelength-domain modeling are supported in 2D and 3D.
When a predefined Electromagnetic Waves, FEM-BEM interface is added from the Optics>Wave Optics branch () of the Model Wizard or Add Physics window, the Electromagnetic Waves, Frequency Domain and Electromagnetic Waves, Boundary Elements interfaces are added to the Model Builder.
In addition, a Multiphysics node is added, which automatically includes the multiphysics coupling feature Electric Field Coupling.
On the Constituent Physics Interfaces
The Electromagnetic Waves, Frequency Domain interface computes time-harmonic electromagnetic field distributions. To use this physics interface, the maximum mesh element size should be limited to a fraction of the wavelength. Thus, the domain size that can be simulated scales with the amount of available computer memory and the wavelength. The physics interface solves the time-harmonic wave equation for the electric field.
The Electromagnetic Waves, Boundary Elements interface is used to solve for time-harmonic electromagnetic field distributions. This interface is especially well suited for radiation and scattering problems since only boundaries need to be meshed and the degrees of freedom (DOFs) solved for are restricted to the boundaries. To use this physics interface, the maximum mesh element size should well resolve the complex electric field on the boundaries. The physics interface solves the vector Helmholtz equation for piecewise-constant material properties and uses the electric field as dependent variable.
Settings for Physics Interfaces and Coupling Feature
When physics interfaces are added using the predefined couplings, for example Electromagnetic Waves, FEM-BEM, specific settings are included with the physics interfaces and the coupling features.
However, if physics interfaces are added one at a time, followed by the coupling features, these modified settings are not automatically included.
For example, if single Electromagnetic Waves, Frequency Domain and Electromagnetic Waves, Boundary Elements interfaces are added, COMSOL Multiphysics adds an empty Multiphysics node. You can add the Electromagnetic Waves, FEM-BEM coupling feature, but no modified settings are included.
Coupling features are available from the context menu (right-click the Multiphysics node) or from the Physics toolbar, Multiphysics menu.
Table 3-3: Modified Settings for a electromagnetic waves, fem-bem Interface
Physics Interface or Coupling Feature
Modified Settings (if any)
Electromagnetic Waves, Frequency Domain
No changes.
Electromagnetic Waves, Boundary Elements
No changes.
Electromagnetic Waves,
FEM-BEM
The Domain Selection is the same as that of the participating physics interfaces.
The Boundary Selection is the same as the exterior and interior boundaries of the Domain Selection of the participating physics interfaces.
The corresponding Electromagnetic Waves, Frequency Domain and Electromagnetic Waves, Boundary Elements interfaces are preselected in the Coupled Interfaces section (described in the COMSOL Multiphysics Reference Manual).
Physics Interfaces and Coupling Feature
Use the online help in COMSOL Multiphysics to locate and search all the documentation. All these links also work directly in COMSOL Multiphysics when using the Help system.
Coupling Feature
The Electric Field Coupling feature is described in the documentation for The Electromagnetic Waves, Boundary Elements Interface.
Physics Interface Features
Physics nodes are available from the Physics ribbon toolbar (Windows users), Physics context menu (Mac or Linux users), or right-click to access the context menu (all users).
In general, to add a node, go to the Physics toolbar, no matter what operating system you are using. Subnodes are available by clicking the parent node and selecting it from the Attributes menu.
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The available physics features for The Electromagnetic Waves, Frequency Domain Interface are listed in the section Domain, Boundary, Edge, Point, and Pair Nodes for the Electromagnetic Waves, Frequency Domain Interface.
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The available physics features for The Electromagnetic Waves, Boundary Elements Interface are listed in the section Domain, Boundary, Edge, Point, and Pair Nodes for the Electromagnetic Waves, Boundary Elements Interface.