13 December 2018
After you insert the 3D component into the project, right click on it's name in the modeler tree and select 'Edit Definition'. It will open as a separate project. You can't modify this particular instance since it's tied to the read-only database containing the built-in HFSS 3D Components. But, you can now select the 'Body' object and copy it to the clipboard and then paste it back into your original model. Now you can delete the 3D component body model and just use this 'Body' object - which you can now freely modify with whatever Boolean operation, etc you want.
The Impedance Boundary Condition was really designed to be used for super-thin layered flat surfaces where meshing the real thickness would be impractical. I've never seen it used to model something this thick but the limit to the thickness according to the HFSS manual is lambda/10 so it should still work. You should also be using the 'two-sided' option and enable 'shell elements'. The one-sided option assumes you have a flat layer external to the model with PEC extending infinitely out on the PEC side. I would highly recommend reading the section of the HFSS help manual titled 'Assigning Layered Impedance Boundaries' very carefully.
Also, are you sure this tube is really 50mm in thickness? Typically there is a large RF birdcage body coil that's built upon a plastic dielectric tube that's closer to ~20-30mm in thickness from my personal experience. The thin copper birdcage coil is on the inner side, and at 3T there's usually a solid copper shield on the outer side. See Figure 1d in one of my MRI publications: https://www.nature.com/articles/srep09805
It also looks like it's modeled as a 3D object from your screenshot? Even if it's vacuum it could add unnecessary mesh elements. I would select the face of a cylinder and use the 'Create Object from Face' command to create the cylindrical surface for which to apply the BC.
I would try using the body as a simple object (not 3D component) as well as making the above modifications to the layered impedance BC and double checking the thickness of that dielectric tube before attempting to hollow out or chop up the body model.
Let me know how it goes!
Peter Serano - Senior Application Engineer - High Frequency Products