Plane Wave Radiation
The Plane Wave Radiation node adds a radiation boundary condition for a plane wave. If required, add an Incident Pressure Field to model an incoming wave. This radiation condition allows an outgoing plane wave to leave the modeling domain with minimal reflections, when the angle of incidence is near normal. Add this node from the Radiation Conditions submenu.
The plane wave type is suitable for modeling open boundaries and ports (in the plane-wave regime only). The condition can be used for waveguide structures as long as they are only interesting in the plane-wave region, but in general the Port boundary condition should be used. When using the radiation condition on an open far-field boundary, it is recommended to construct the boundary such that the incidence angle is near to normal. This of course requires a priori knowledge of the problem and the solution. See the theory section Theory for the Plane, Spherical, and Cylindrical Radiation Boundary Conditions for details about the equations and the formulation of this nonreflecting boundary condition.
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An estimate of the reflection coefficient Rs, for the spurious waves reflecting off the plane wave radiation boundary, is, for incident plane waves at angle θ, given by the expression:
where N is the order of the boundary condition (here 1 or 2). So at normal incidence (θ = 0), there are no spurious reflections, while, for example, at an incidence angle of 30o for N = 2 (plane wave radiation in the frequency domain), the amplitude of the spurious reflected wave is 0.5 % of the incident.