From what I’ve been able to figure out, COMSOL doesn’t really know how to mesh bulk metals (where the minimum dimensions are much greater than the rf skin depth) intelligently. There is no rf field inside bulk metals, so it shouldn’t be necessary to mesh the metals – other than their surfaces.
Yes, it is in principle possible to exclude all of the interior of bulk metals from the problem, mesh the rest of the problem, define the boundaries between the bulk metals and the rest of the problem as impedance boundaries, and get it to work. I have gotten this to work on simple problems, where there may be a dozen or so domains and only a few simple bulk metal parts to be excluded from the problem. But there doesn’t seem to be a practical method of doing this where there are hundreds of complex metal parts, thousands of surfaces, many ports, etc.
I’ve tried boundary layer meshing on some complex parts, but this feature seems to be directed at CFD problems, and seems much worse than free tetrahedral for bulk metals in rf problems. Sweeping surfaces also seems to be prohibitively complex when dealing with a large number of very complex geometries.
My real problem is that I’m trying to substantially reduce the number of mesh elements in an extremely complex rf/microwave problem. I’m currently at ~10M DOFs, and it may grow to more than 50M DOFs before I’m through with it if I can’t figure out an easy way to exclude all of the metal parts from the problem.
Our geometry includes a lot of various shaped small metal and ceramic parts, surrounded by air (or vacuum). The only way we’ve gotten satisfactory meshes thus far has been to first mesh all the small parts (in some carefully chosen magical order) and then mesh the surrounding vacuum space.
It would be great if there was a simple method of telling COMSOL to just mesh the boundaries of a selected domain with a triangular mesh (with suitable controls), make those surfaces impedance boundaries, and exclude that domain from the emw solver. That would probably allow us to get working meshes with at least 30% fewer mesh elements, and that is a huge deal when we’re talking about more than 5M mesh elements.
Is there some way to do this, that I’ve missed? If not, it seems this is a capability COMSOL should be working on adding.
David