Scattering Boundary Condition
Use the Scattering Boundary Condition to make a boundary transparent for a scattered wave. The boundary condition is also transparent for an incoming plane wave. The scattered (outgoing) wave types for which the boundary condition is perfectly transparent are
The field E0 is the incident plane wave that travels in the direction k. In addition, to an incident plane wave, E0 can also be the electric field distribution for a Gaussian beam that propagates in the direction k. The boundary condition is transparent for incoming (but not outgoing) plane waves with any angle of incidence. When Wave Vectors are set to unidirectional, the direction k is provided automatically from the wave vector k1 specified for the physics interface. When Wave Vectors are set to bidirectional, the user selects whether the direction k is provided from the wave vector for the first wave k1 or the wave vector for the second wave k2.
The boundary is only perfectly transparent for scattered (outgoing) waves of the selected type at normal incidence to the boundary. That is, a plane wave at oblique incidence is partially reflected and so is a cylindrical wave or spherical wave unless the wave fronts are parallel to the boundary.
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For cylindrical waves, specify around which cylinder axis the waves are cylindrical. Do this by specifying one point at the cylinder axis and the axis direction.
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For spherical waves, specify the center of the sphere around which the wave is spherical.
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When Wave Vectors are set to bidirectional, specify which wave the specified input field is associated with.
A Reference Point subnode can be added by right-clicking the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu. The Reference Point subnode redefines the incident field to be expressed as
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where rref is a reference point determined as the average point from the point selection in the Reference Point subnode.
If the problem is solved for the eigenfrequency or 2D axisymmetric geometry, the boundary condition does not include the incident wave.
Scattering Boundary Condition
When Wave Vectors is set to bidirectional, you specify with Input wave which wave the specified input electric field is associated with.
Select Incident field to specify whether there is No incident field (the default), the input wave is specified by the electric field (Wave given by E field), the magnetic field (Wave given by H field), or as a Gaussian beam (Gaussian beam).
Specify the Incident electric field E0 (SI unit: V/m) or Incident magnetic field H0 (SI unit: A/m), depending on the setting of Incident field.
If the Incident field is set to Gaussian beam, select an Input quantity: Electric field amplitude (the default) or Power. If the Input quantity is Electric field amplitude, enter the component expressions for the Gaussian beam electric field amplitude Eg0 (SI unit: V/m). If the Input quantity is set to Power, enter the Input power (SI unit: W in 2D axisymmetry and 3D and W/m in 2D) and the component expressions for the Gaussian beam non-normalized electric field amplitude Eg0 (SI unit: V/m). Also edit the Beam radius w0 (SI unit: m) and the Distance to focal plane p0 (SI unit: m). The default values are ((10*2)*pi)/ewfd.k0 and 0 m, respectively. The optical axis for the Gaussian beam is defined by a line including a reference point on the feature selection with a direction specified by the propagation direction for the selected Input wave (for unidirectional propagation it is the direction of k1). By default, the reference point is the average position for the feature selection. However, by adding a Reference Point subnode any available point (or the average of several selected points) on the feature selection can be used as the reference point. The focal plane for the Gaussian beam is located the Distance to focal plane p0 from the reference point in the propagation direction for the selected Input wave.
Select a Wave type for which the boundary is absorbing — Spherical wave, Cylindrical wave, or Plane wave.
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For Cylindrical wave enter coordinates for the Source point ro (SI unit: m) and Source axis direction raxis (dimensionless).
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For Spherical wave enter coordinates for the Source point ro (SI unit: m).
For more information about the Gaussian beam theory, see Gaussian Beams as Background Fields and Input Fields.