define new material HFSS

I start work in HFSS but I have a Problem , I work on material that have
changeable behavior versus frequency so I want to define it by its two
parts (real and imaginary) of impedance versus frequency but Till now I do not know how
i can do that by HFSS?

right click the object, select assign material, click add material. The material properties are not directly assigned impedance since that is going to be a derived property depending on the geometry. The impedance change with frequency is calculated for you based on material properties for your geometry. In general static values for the material properties are accurate enough, but if you're doing something really sensitive that is very wideband you may want to set frequency dependence of materials. There are even standard models for frequency dependence. Be careful since this can lead to non causal solutions.

THANKS reidintransit but unfortunately till now i can not do it , I try what you said befor but it is not the same with material

You can assign lumped ports with real and imaginary impedances. Maybe that's what you are going for?

lumped not possible for defining graphene , because I have varied impedance at every frequency

http://en.wikipedia.org/wiki/Wave_impedance
You don't input impedance directly, you need to imput each part that contributes to the wave impedance separately. my previous post says how to do so for each parameter.
Z = sqrt(jw*permeability/(conductivity+jw*permitivity))