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 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), Incident magnetic field envelope H0 (SI unit: A/m), or Gaussian beam electric field amplitude Eg0 (SI unit: V/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 Incident field is set to Gaussian beam, 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.