CST： Define a Time Dependent Dielectric Constant of a material

Hi all,
I am using CST MWS, I need to know how can we design a material with Time Dependent Dielectric Constant (epsilon). There is a provision of defining a Time dependent Conductivity of material in CST, but i want a lossless time varying dielectric medium. I don't know how to do? Please Help me.
Thank you

A dielectric, and time dependent behavior, involve capacitance.
Capacitance (and inductance) involve phase changes.
With a phase change, there is always unavoidable loss.

thanks
I am absolutely agree with you. But in my case, Time varying dielectric constant means "let's suppose if field is propagating in a dielectric medium with a constant permittivity & after some if the permittivity of medium is changed to a fixed value because of an external factor". How to create this phenomena in single simulation model in CST? I don't think introducing conductivity will help here. I am using a Time Domain Solver.
Thank you

From what I have seen CST does not have the ability to change permittivity/permeability with respect to time. You are going to have to make a custom code for that. If would recommend Finite-difference time-domain (FDTD). There is a great section about it here:
http://emlab.utep.edu/
Go to the academics section.