Negative index of refraction - confirming using HFSS?

I'm involved in a project aiming to simulate, and later hopefully build, a negative lens for operation at 100GHz....a major stumbling block is extracting μ and ε from our HFSS simulations.

There are a lot of very vague articles that claim to have achieved 'doubly negative' parameters, which don't actually explain how they confirmed this.

Does anyone know of a (reasonably) simple way of extracting μ and ε? Or if all else fails and this is not possbile, could we prove the material is exhibiting a negative n value without actually going into detail about the parameters?

Any hints would be much appreciated!

I think you can simulate your material and see its behavior with an electromagetic wave, to show the inversion of Snell's law, this can do and viewable by Hfss.

I once simulated a periodic SSR structure and could see (animated E-field) a wavefront travelling backwards. It was only a wavelength long and wide and close to the SRR, but it looked very interesting!

I was looking for a way to find out n, but you have to extract magnitude and phase from the Matrix data. Since my primary work ist not about MM, I did not work on it any further.