Thin films (400nm) in HFSS

[vfurlan]

Hi,

I designing a slot antenna on a alumina substrate. On Alumina I also added a ferroelectric thin film (400nm) to analyze if I can tune the antenna with it. Model dimensions are about 8x7cm.
To converge HFSS requires a huge number of tetrahedras (about 600 000). A friend of mine told me that non the less the ratio of the biggest and smallest dimension (cm and nm) is too big and HFSS will not do a good job in 3D meshing of thin film. Is this true?

Thx

 

[sweetjimmy]

Generally speaking, you can replace extremely thin films in HFSS with either an impedance boundary condition or a layered impedance boundary. Consult the online help for more information. The issue with thin objects is not that HFSS won't do a good job of meshing the films. It is the fact then when you get long,skinny tetrahedra, the results become less accurate. This has to do with the fundamental method underlying HFSS.

One way around this is to select the thin layer, and go to HFSS / Mesh Operations / Assign / Surface Approximation. From there, set the Aspect Ratio setting for about a 5:1 ratio. This will drive up the number of tets, so you also might want to invoke the Iterative solver in the Adaptive Setup options to reduce the memory required. One other option would be to change the order of the elements to Mixed to make the meshing more efficient.

 

[vfurlan]

How does layered impedance boundary work? If I have antenna substrate with thickness X, on it I place layered impedance boundary with 400nm thickness, where I have to put the copper above it? On X or on X + 400nm?

 

[ferdows]

hi
its hard to judgement about an antenna with out data about frequency as i understand your antenna not very small its size like a GSM frequency antenna and at this frequency u applied a thin film ferrite i think at this frequency and size ferrite dose not have benefit or affect
so pls give more information u send your simulation

 

[vfurlan]

hi
its hard to judgement about an antenna with out data about frequency as i understand your antenna not very small its size like a GSM frequency antenna and at this frequency u applied a thin film ferrite i think at this frequency and size ferrite dose not have benefit or affect
so pls give more information u send your simulation

Well, now I'm trying to understand if my idea is good. That's why I'm running the simulations.
What about my question about Layered impedance boundary?

 

[ferdows]

hi
what u mean? i cant understand impedance boundary

 

[vfurlan]

So, I place Layered Impedance boundary with 400nm thickness, and above it I want to place another box. Do I have to place this box directly on the boundary or I have to leave 400nm of space between?