# FEM Absorbing Boundary Condition

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I am trying to simulate a sphere over a half planar anisotropic material. I am using the MoM for the sphere and FEM for the material. Since I would like the substrate to be half planar, I have decoupled the MoM and FEM solutions and applied the absorbing boundary condition. Although the air buffer region that surrounds the FEM region prevents the material from being on the boundary which defeats the purpose of the absorbing boundary condition. Am I understanding this properly? and if so is there away around this?

Cheers,

Patrick

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Hello Patrick,

I'm not sure I understand what you are doing or what your question is. If you have a picture or a model, that would probably help.

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I have attached my model. I would like for the rectangular slab to have infinite extents laterally. I would use a half planar greens function, but the slab is anistropic. Since it is an anisotropic body I need to have an air buffer surrounding it. When I apply the FEM absorbing conditions, the boundary of the FEM region is now the air buffer as opposed to the anisotropic body that I am interested in. Am I correct in my understanding of the absorbing boundary condition? and if so can I apply it in such a way as to get close to what I am looking for?

Cheers,

Patrick

PEC.cfx

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Hi @pmcardle,

please excuse the delay in answering. I now had a look at your model, but I'm still not sure I fully understand. You defined an air region (FEM) around the anisotropic body to make it infinite in x and y, correct?

1. An air region will not extend the anisotropic region, it just adds air.
2. The air regions is defined only 0.01 µm thicker than the aisotropic region, which results in obvious meshing problems:

Presently I don't see a way to simulate infinite anisotropic layers. I would put a large air box around and solve everything with FEM, see PEC_alt.cfx

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