The Plane Wave Radiation node adds a radiation boundary condition for a plane wave. If required, from the Physics toolbar, 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 to normal.
The plane wave type is suitable for both far-field boundaries and ports. Because many waveguide structures are only interesting in the plane-wave region, it is particularly relevant for ports. 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.
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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:
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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 at an incidence angle of 30o for N = 2 (plane wave radiation in the frequency domain), for example, the amplitude of the spurious reflected wave is 0.5% of the incident.
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Automotive Muffler: Application Library path COMSOL_Multiphysics/Acoustics/automotive_muffler
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