# HFSS giving wrong solutions half the time

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#### mhaghaed

##### Newbie level 5
I've used hfss to simulate an on-chip inductive coupling link at 433MHz. Everything was perfect and the results were close to the values I got from ASITIC. I saved separation as a design parameter and changed that from 1cm-10cm accordingly and everything looked fine in 3D view.However, when I changed the coil separation from 1cm to 10cm, it gave me a wrong answer with negative resistance and mH(!) inductance values. Can anyone tell me if he has similar experience

#### Abhishekabs

What are you getting for seperation of 2cm, 5cm ?
How much deviation is there?

Need to check step by step.

### mhaghaed

Points: 2

#### mhaghaed

##### Newbie level 5
with an airvolume width of 2cm:

separation = 0.5cm ->OK
separation = 1.5cm ->OK
separation = 4.5cm ->Does not even simulate, it encounters some problem while meshing and says it might be because of skewed thin surfaces

Increasing airvolume width to 1meter does not help at all

#### Abhishekabs

so that we can check.

Without understanding project it will not be correct to comment on error.

#### mhaghaed

##### Newbie level 5
OK, now it doesn't simulate at all. Can you tell me how I can overcome the following:

"Surface Recovery failure Possible reasons : (1) . model has multiple objects with thin layers (2) complex model with object overlapping (3)" True surfaces are skewed "

Hassan

#### Abhishekabs

This sounds like geometry fault,
How you are changing your width or spacing?
I dont know how your geometry looks like, but I think you have not created geometry with proper operations such as subtraction or uniting objects etc.

Try creating the geometry by different method and simulate.

Best of luck.

### mhaghaed

Points: 2

#### mhaghaed

##### Newbie level 5
My geometry consists of two thin-sheet coils(mm-sized) buried in dielectrics that are separated far from each other(1cm+).

I tried specifying some mesh operations to help it in meshing the structure, but it still gave me the same error.

#### Abhishekabs

BR,
Abhishek

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