rautio said:To check skin effect in any em analysis:
1) Make sure your mesh size in the metal is small compared to the skin depth.
2) Look at the resulting current distribution in 3 dimensions. Do you see the skin effect? Does the current distribution look smooth, with very strong high edge current?
Of course, at low frequency, you should see uniform current everywhere, no skin effect. All EM analyses I know of (including our own Sonnet) can give bad answers if you push them too far. Current distribution is very sensitive to error and is thus excellent for finding problems.
"How small of a mesh is small enough?" is a fair question. Just cut the mesh size in half in all three dimensions in the metal, and reanalyze. Hopefully, the difference will be small. If so, you are OK. If not, keep refining.
For line thickness less than about 5 or 10 skin depths, the above suggestion of "solve inside", or the equivalent in Sonnet of the multi-sheet thickness model, is a good one, provided the mesh is small enough.
For thicker lines, the tube-like model (in HFSS, this is "do not solve inside") that uses an equivalent surface impedance and surface currents should be plenty accurate enough (but always check these things for yourself, if it is important!). @gilent Momentum also has a tube-like model that can be used as well. Sonnet does not have a tube-like model. I don't think you would want to use the tube-like model at lower frequencies, where current flows through the entire body of the conductor, not just on the surface. An expert user can fudge the surface resistance to get the correct low frequency bulk resistance, but the inductance and capacitance will still be off. Unfortunately, it is difficult to check convergence (i.e., cut the mesh in half) with the tube-like model.
There is much more to this than what I have described above, but these should serve as initial talking points if anyone is interested.
rautio said:Ruri -- If you intend to tie it to ground, then proceed to tie it to ground, presumably with vias. Be sure to put the vias in the same place in your EM analysis as you do in your actual circuit. If the gaurd ring makes no difference in the EM analysis, then it is not acting to decrease loss. The only thing it could do is decrease coupling to other nearby components. To check to see if it is doing that, analyze two inductors side-by-side with gaurd rings and without. If there is still no difference, then, best as I can tell, your gaurd rings are doing nothing but taking up space. All your ground return current is flowing in the substrate. In this case, throw the gaurd rings out and make your circuit smaller. Just be sure to check for unwanted component-to-component coupling via the substrate. Let us know what you find out, sounds interesting!
Hi Amaya,Hi everybody,
I´m simulating spiral inductors in HFSS and comparing the results with Momentum simulations. There are important differences between them, so, I think something is wrong in my HFSS structure.
I sent it attached, could anyone look at it and give me a hand????
thank u in advanced!
amaya
rautio said:There is a way to eliminate the additional loss caused by current crowding, I can describe it if there is interest.
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