Hi,

It's very easy. You might be working on metamaterial. To define negative permittivity and permeability, go to assign material, define new material and then define negative value of mue and epsilon under the given box.

All the Best,

I tried assigning negative values in defining new material. But it does not takes the value. Or if the value is taken, the results are not relative.

Hi Vignesh,

CST uses transient solver which doesn‟t support negative permittivity and permeability. We can‟t enter negative permittivity and permeability values for any substrate directly. 

Negative permittivity and permeability values can be entered using HFSS, which is based on finite element method.

You need to understand the exact meaning of metamaterial. There is no material which is having negative permeability and permittivity (atleast not discovered yet). We designed the structure whose effective permittivity and permeability becomes negative and that too happen only a specific frequency when the field profile become opposite. In general, transient solver cannot solve maxwell's equations for negative values.  Please read this article to understand the meaning of effective value of permittivity and permeability. Check the following link for CST

https://www.youtube.com/watch?v=DxXR_hyDR1Q