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Solution Number: 977
Title: How do I turn an interior boundary into a perfect conductor in my In-Plane TM Waves model?
Platform: All Platforms
Applies to: COMSOL Multiphysics, Electromagnetics Module, RF Module
Versions: 3.3, 3.4
Created: January 4, 2006
Last Modified: February 22, 2008
Categories: Boundary Conditions, Electromagnetics
Keywords:

Problem Description

I am using the In-Plane TM Waves application mode in the RF Module. I would like to embed a perfect electric conductor, but this boundary condition is available only for exterior boundaries. Why is this, and how can I turn an interior boundary into a perfect electric conductor?

Solution

An internal Perfect Electric Conductor (PEC) condition in the In-plane TM waves application requires that the solution variable, Hz, be discontinuous across this boundary. The standard nodal mesh elements that COMSOL Multiphysics uses impose continuity in the solution variable across internal boundaries. This is because the mesh elements on both sides share the same nodes on the boundary. Using an assembly lets you decouple the nodes on the boundary.

To impose a PEC condition on an interior boundary, proceed as follows:

  • In the Draw mode, make sure that your PEC boundary constitutes the border between two separate objects.
  • Select Draw > Use Assembly.
  • You should now have two boundaries where you want your PEC boundary condition. Select the PEC boundary condition, which will now be available, for both these boundaries.
  • Any other borders between your objects will also be double boundaries. To make the solution continuous across these boundaries, you will need to turn them into identity pairs. Do this from Physics > Identity Pairs > Identity Boundary Pairs.

The supplied example model shows an incoming plane TM wave as it is scattered by a thin perfect electric conductor plate. The model uses the scattered field formulation and solves for three different angles of incidence. The parametric solver varies the angle of incidence, which enters the model through the expression for the incident magnetic field, specified under Physics > Scalar Variables. A cylindrical perfectly matched layer (PML) surrounds the physical domain in order to avoid unphysical reflections at the exterior boundaries. To enhance visualization, the PML subdomain and the continuity boundary pairs have been suppressed, using Options > Suppress.

The image shows the z component of the magnetic field at a 45 degrees angle of incidence. Click to enlarge it.

The general procedure outlined here is described in more detail under "Using Assemblies" and "Specifying Physics Settings on Pairs" in the COMSOL Multiphysics User's Guide. For a fully documented example, see the Thin-Film Resistance model in the Model Library, under COMSOL Multiphysics > Electromagnetics.

See also Knowledge Base 902.

Related Files

PEC_in_TM.mph 3.7 MB


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