Photonics

Metamaterial

Subscriber

Hello,

I am simulating a 2D matamaterial with FDTD in the range of 3-80GHz.

I am trying to simulate a 2.5mm thick plate, with permittivity of 20 and permeability of 1.

I used the grating S-parameters to calculate the S-parameters, and then I used Smith's script to extract the effective parameters.

The problem I encountered is that when I plotted the effective index, impedance, permittivity and permeability curves, I have a weird result with a lot of fluctuation (see attachment), knowing that the initial values are correct and S_abs and S_phase seem correct.

And I want to know if there is a way to plot the S phase directly in degrees rather than radians?

• Guilin Sun
Ansys Employee
It is obviously that the result is distorted by the phase over 2pi as you can see the phase of S11. Since you are simulating a spectrum range more than 10X higher than the beginning frequency, it is normal to have phases over 2pi. Unfortunately the complex results automatically remove the extra phase, which you may need to add them back.
Our current method based on Smith' method does not consider this extra phase change. There are some published methods which may handle this but need extra efforts. Please search some online.
Subscriber
What intrigues me is that when I use a frequency range between [5-20GHz], I noticed that the material influences the effective parameters, i.e. for materials with low permittivity (e.g. eps=5) and with a non-zero imaginary part, I find correct results but if I put the imaginary part zero, in this case I find the fluctuations.
and for materials with high permittivity (eps>10) I always find the fluctuations after the extraction of the effective parameters whatever the imaginary part (null or not).
Do you think that the permittivity of the material influences the effective parameters?
Do you have an idea to solve this problem?