Discussion Forum

Hi!

I am currently working with the RF module (electromagnetic waves) in the Comsol 4.0a version. Basically what I am trying to do is to simulate a wave propagation in a spherical waveguide (made out of two concentric spheres). The signal is introduced into the waveguide through a coaxial cable and it is measured by means of another coaxial cable which is placed just symmetrically.

The only special characteristic of this structure is the size difference between the coaxial cables and the waveguide: spherical waveguide is three times bigger than the coaxial cables.

What I need to do is to apply a different mesh size in the structure: I need both coaxial cables to have an extremely fine mesh and the spherical waveguide to have a coarse mesh (in order to reduce the execution time).

It is just this meshing what I have been struggling with. My first test was to follow the meshing steps given in the document “coaxial to waveguide coupling” just because my model is similar to this one. I was unable to mesh my structure because I obtain the following errors:

1. Error:
“Failed to insert a point … An empty cavity was generated”

2. Error:
“Failed to generate mesh for domain->Failed to respect edge element on geometry edge->Internal error in boundary respecting”

Reading some of the discussion topics of the Comsol webpage I tried to begin meshing the smaller parts of my structure and then the bigger ones (I even created some intermediated boundaries) ; in this case the most of the times I end up with a “Failed to generate mesh for domain” (with the domain belonging to the sphere).
I have been working with two different structures: one defined in the CAD program Rhinoceros and the other designed with the tools given in Comsol interface.

Does anyone have a problem similar to mine? I have been reading all the discussions of the forum and trying some of the ideas given but I do not get anything from it.

By the way, I was finally able to mesh the model made in Comsol but when simulating it I end up with a non transmission of signal (the S21 parameter is zero for each frequency): Could it be that when applying different meshing sizes there is no continuity between domains and therefore the signal is not transmitted from the coaxial cable to the waveguide (and hence it does not arrive to the output)?

Thank you very much for any idea or suggestion given,

Cristina Cocho