Help me with excitation of capacitor in HFSS

i'm looking for an example for capacitor modeling using hfss, can anyone help me with this?, i have drawn the circuit but the excitation has given me false results

thanks

Re: capcitor simulation

If this is a planar capacitor, you should use any planar tool (Sonnet, Momentum, EMSight, etc.), you should not use volume meshers. Planar tools handle the very thin dielectric layers extremely easily, volume meshers struggle in such cases. You can very likely do your entire capacitor (if it is planar and no more than 2 metal layers) using free SonnetLite, www.sonnetsoftware.com (I work for Sonnet).

Installing SonetLite takes about 2 minutes. Then you have to wait a few minutes to get the full license (it is automatically emailed to you). Then about 45 minutes on the tutorial (Help->Tutorials), then you are ready to go. Depending on the complexity of your capacitor, I would guess in about 1 hour you will have results.

If your capacitor is not planar, you pretty much have to use a volume mesher. Expert HFSS users can seed the mesh to get good results. CST has some intelligent meshing routines that work well and I would recommend (my company represents CST in North America).

Re: capcitor simulation

Actually it's not a planar capacitor , i'm simulating vertical parallel plate structures and horizontal bars structure , beside i thought hfss is the most accurate simulator in modeling such structures. so i need any application note to start the mopdeling job.

so if anyone have an example or an application note talking about this , i'd be glad to receive it.


thanks

Re: capcitor simulation

Hi midolasi3 -- All the EM tools are the most accurate for one problem or another. No one has a monopoly on accuracy for all problems.

If you have thin dielectric in your capacitor, CST can use their PBA (perfect boundary approximation) that allows up to three different materials to pass through each cell with their boundaries perfectly represented. I think it is likely CST will give a superior answer for such a problem, but would be good to see the problem in detail first.

In general, if you want to quickly check accuracy, look at the current distribution for each EM analysis of a circuit. Current distribution is very sensitive to error. The EM analysis that provides the smoothest current distribution with very strong current on all sharp edges is usually the most accurate. If you need to use HFSS and want high accuracy, I would suggest continuing to refine the mesh until you get a good looking current distribution.

For the result you already have, have you checked the current distribution? It might give you a clue as to where your mesh should be seeded. Seems like there are enough expert HFSS users around, someone could give you a hint on how to seed the mesh for this problem.

Re: capcitor simulation

Hi all

I've already simulated the parrallel plate capacitor using Sonnet software ( it was a part of their examples ) and got good results , i've drawn the same structure on HFSS aiming to obtain the same results but i've problem with excitation , so can anyone tell me
1.which type of port to use & what are the guidelines for using such port ?
2. what are the rules for seeding the mesh for obtaining accurate results ?

ps: i'm performing such simulation for extracting the high frequency spice model for such capacitor

Thanks

Re: capcitor simulation

midolasi3 said:

Hi all

I've already simulated the parrallel plate capacitor using Sonnet software ( it was a part of their examples ) and got good results , i've drawn the same structure on HFSS aiming to obtain the same results but i've problem with excitation , so can anyone tell me
1.which type of port to use & what are the guidelines for using such port ?
2. what are the rules for seeding the mesh for obtaining accurate results ?

ps: i'm performing such simulation for extracting the high frequency spice model for such capacitor

Thanks

Click to expand...

1. You can use lumped port to directly connect those two parallel metal plates, just make it as small as possible.
2. For seeding, you can assign it through meshing properties after selecting objects. You may specify the aspect ratio of mesh cell, or you may specify the largest dimension of each mesh cell.

Yes, I agree with Rautio, volume mesh is not a efficient tool for this kind of simulation, especially you need to take the metal loss into consideration.

Regards,

Re: capcitor simulation

i did similar analysis with HFSS. I used waveport and used a parallel plate waveguide to send signals to the plates (with de-embed so that the TR.line effects are removed). The results are ok for more than 1GHZ but when i go very low the calculation using formula for S11(s11= -jwczo/(2+jwczo) gives negative cap....im struck there...!!! help

Re: capcitor simulation

can MEMS structures be simulated with sonnet?.