Use the Matched Boundary Condition to make a boundary transparent for a wave (or waves) with the phase(s) as prescribed in the
Wave Vectors settings of
The Electromagnetic Waves, Beam Envelopes Interface settings.
Since the Wave Vectors settings are taken into account, this boundary condition is low-reflecting also for waves propagating with a large angle to the normal of the boundary, in contrast to the
Scattering Boundary Condition, where the scattered beam should propagate almost in parallel to the boundary normal to be efficiently absorbed.
If there is an incident field, 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
where rref is a reference point determined as the average point from the point selection in the
Reference Point subnode.
When Wave Vectors is set to bidirectional, select an
Input wave —
First wave (the default) or
Second wave — that the specified input electric field is associated with.
Select an Incident field to specify whether there is
No incident field (the default), the input wave is specified by an
Electric field, a
Magnetic field, or a
Gaussian Beam.
Specify the Incident electric field envelope E0 (SI unit: V/m) or
Incident magnetic field envelope H0 (SI unit: A/m), depending on the
Incident field selected. Notice that you only specify the envelope factor of the incident electric or magnetic field. The envelope function is internally multiplied by the phase function, as specified in the
Wave Vectors settings, to form the complete incident electric or magnetic fields.
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
Input wave (or
k1 for the unidirectional formulation). 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
Input wave (or
k1 for the unidirectional formulation).
When Wave Vectors is set to bidirectional, if no scattered field is expected, select the
No scattered field check box. This prevents COMSOL from returning spurious solutions that otherwise could appear between boundaries with unconstrained scattered fields.
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