The Perfectly Matched Boundary is effectively a perfectly matched layer (PML) that is applied to the open boundary without the need to define a domain (a layer in the geometry). The condition automatically applies the PML formulation using the extra dimension functionality of COMSOL Multiphysics.
Select the Attenuation direction as
Radial (the default),
Normal, or
Custom. For the
Radial option enter the
Center coordinate r0, that is a coordinate that approximately gives the location of the radiation source. The
Radial option works well for most open problems and it will be applicable for most geometries of the radiation boundary. The
Normal option will apply the attenuation in the normal direction to the boundary where the condition is applied. In this case the shape of the radiating boundary is important. For the
Custom option enter the
Custom attenuation direction in the edit fields.
For the Logarithmic,
Polynomial, and
Rational options enter the
PML scaling factor and the
PML scaling curvature parameter. The default values depend on the selected
Coordinate stretching type. These settings correspond to the settings entered for the classical
Perfectly Matched Layers (PMLs). When
User defined is selected choose the functions to be used for the real and imaginary part of the stretching functions, respectively. These should be
Functions defined under the
Definitions node.
Enter the Number of mesh points, the default depends on the selected
Coordinate stretching type. This represents the mesh resolution in the PML along the extra dimension.
Select Use uniform thickness (not selected per default) to enforce an equivalent uniform thickness in the attenuation direction. This option is only available when the
Attenuation direction is
Radial. If selected a slight gain may be achieved in numerical precision, but the performance/convergence of iterative solvers may be compromised. For spherical geometries this will make the attenuation behave as a PML with the same settings and a uniform mesh.
