Eigenmode Solver "did not converge based on specified criteria." ???

[tranquiltension]

Hey Everybody,

I'm using HFSS version 12 to solve for the eigenmodes of a double-dielectric material that is thought to act as a DNG metamaterial around 17 GHz. I've been searching around the Brillouin zone for my little window around 17 GHz to no avail until recently. I had to be very specific with the eigenmode solver - telling it to start looking for modes at 17 GHz.

I seem to have stumbled upon the eigenmodes that I'm intested in around 17.2 GHz, but the solver is very touchy about finding them. I'm following this guide and it's worked for other frequencies, but around 17.2 GHz, I have to lower my step size significantly to see any real behavior.

What's bothering me is that I keep getting the message like this:

    [info] A variation (px='180deg' py='54deg') has been requested on machine Local Machine (12:34:16 AM  Apr 30, 2011)
    [warning] Adaptive Passes did not converge based on specified criteria. (5:44:59 PM  Apr 30, 2011)
    [info] A variation (px='180deg' py='57deg') has been requested on machine Local Machine (5:45:01 PM  Apr 30, 2011)
    [warning] PML group 'PMLGroup1' part 'PML_Air1' is contained by object 'Space' (5:45:01 PM  Apr 30, 2011)
    [warning] Adaptive Passes did not converge based on specified criteria. (10:11:36 AM  May 01, 2011)

So it seems to me that the eigenmode solver was unable to locate an eigenmode at px=180, py=57. When I look at my results, however, there is clearly a result at these values.

Should I trust these results? For these eigenmode runs, I'm using a mesh that was generated from a previous run that had 100% convergence. I have the solver looking for only ONE mode with REAL frequency. I have max delta frequency set at 10%, and the maximum number of passes set to 3. My minimum solution frequency is 17 GHz.

Any ideas would be helpful.

Thanks,
TT

 

[sweetchoto]

Hi TT,

Eigenmode solver is extremely sensitive and if convergence is not achieved as you have mentioned you cant really trust the results. The guide you are following is a small portion taken by the Guide available on Ansoft website namely 'Metamaterial'. I would strongly suggest you to download it from there and you will find very helpful tricks from there in order to make sure that adaptive passses converge on your frequency of interest. It is free to download and anyone can have it. I dont remember exactly but i have already uploaded this document here on this site in some other thread. You can search for it here aswell.

Hope it helps you.

/SC

 

[tranquiltension]

Hey SC,

It's been a while since we've last corresponded. Thanks for the ideas. I've used the metamaterial document from Ansoft (Left-Handed Metamaterial Design Guide) before. I'm following it pretty closely.

I've gone ahead and reduced the number of converged passes from 3 to 1, in hopes this would help. I'm really hoping this whole thing hasn't turned out to be some awful numerical error...