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Open boundary conditions are designed to absorb or attenuate any radiation that intersects the boundary so that little or no radiation is reflected back into the defined geometry. The function of the open boundary condition is to truncate a geometry or system without disturbing the fields so that it becomes possible to describe an infinite space or an infinite waveguide, within a finite simulation domain. Radiated fields from the antenna are attenuated by many orders of magnitude upon reflection from the boundary so that the antenna does not "see" the boundary.

Simulator Applicability

3D Driven Frequency (RF3p)

2D Eigenmode (OM2p)

3D Eigenmode (OM3p)

Common Uses

To absorb or attenuate radiation. PML is typically used only in antenna or other intentionally radiating structures.


Must be applied only to exterior faces.

PML must be applied either to planar faces or spherical surfaces.

In a simulation where an antenna operates in unbounded free space, the antenna must be enclosed by either a rectangular volume (such as a large air-filled cube) or a volume that is made up of one or more quadrants of a sphere (where the flat sides are ground planes or symmetry boundaries).


Each open boundary condition involves a trade-off between speed and accuracy. In general, Approximate Open offers moderate accuracy and add very little to the computational overhead. For high accuracy, when computational speed is less important, PML is a good choice.


Label - A unique name that identifies the attribute. (IAttribute/Label)

Color - Color used on objects to which this attribute is applied. (IAttribute/Color)

Type - Type of open boundary condition. (IFDOpen/Type)

  • Approximate Open - An impedance boundary condition with the impedance of free space. If the Approximate Open boundary condition is in the electromagnetic far field, this is a good approximation.

  • PML - Defines an auxiliary mesh that adjoins the main finite element mesh at the surface that has the PML boundary attribute. This auxiliary mesh is filled with lossy media that is impedance-matched to the adjacent main mesh, so that incident fields penetrate the PML mesh with low reflection, and those fields are attenuated in the PML material. Field attenuation within the PML depends on the incident angle of the fields that intersect the PML boundary: normally incident fields experience optimal attenuation, while glancing fields experience less attenuation. The PML accuracy is inversely tied to its computational burden: a PML that attenuates fields at the boundary by more than 60 dB contributes more significantly to the computational load, while a PML that attenuates fields by about 30 dB contributes less to the computational load. Three options for the PML level are offered so you can select one based on the computational and accuracy requirements of your particular geometry.

Level - Controls the quality of the PML which can greatly impact the computation burden of the PML. Only visible when type is set to PML.

Example Creation Script

Open_1 = AttributeSet_1.NewBoundaryCondition("FD_Open", "Open_1")

Scripting Interfaces


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