Hello all,
Based on a tutorial about meta-material I simulated the cell in CST software. However, some hidden aspects of this simulation is unknown to me.
1) Why did the tutor use waveguide port at the side wall instead of front of the cell?
2) If I use open boundaries conditions in CST software I get the different results and I must use the same boundaries condition( where I couldn't understand where they came from) such as magnetic and electric filed on specific planes.
I will be grateful if you kindly let me know how we set the waveguide position and boundaries condition for different planes or different structures.
Hi.. Here's the solution...
For these kinds of cells, you can use either magnetic/electric boundaries or unit-cell boundary condition. For magnetic/electric boundaries you need to define wave-guide ports but for unit-cell boundary condition, there's no need to define port. It defines two ports automatically. The answer of your questions: 1) Maybe the application is in a way that justifies that direction of feeding. You can choose your desired direction based on the application. As far as I am concerned, for FSS structures, the incident direction is Normal to the surface. 2) First, Open boundaries are not suitable for analyzing meta,aterial cells as we tend to ignore the edge diffraction when dealing with these periodic structures. Let me clarify that in these cases, we use open boundaries only for finite structures. Second, Magnetic/electric boundary conditions come from the fact that we want to create a plane wave (TE or TM mode) using wave-guide port which is not useful for producing planewaves. As a result, you use this configuration to create your desired TE/TM wave toward the cell. Keep in mind that you need to check the port modes frequently to ensure that it excites a correct wave distribution. I don't recommend it (using wave-guide port for cell analysis) as it has got many limitations. Instead, you can use plane wave incidence or unit-cell ports in your desired direction.
Do you want to retrive the S parameters of the metamaterial unit by using plane wave in free space?
If you do...
Firstly, the boundary conditions you set is the simulated the plane wave, so, the E-field perpendicular to the magnetic field, also, the H-field lines are perpendicular to the SRR plane, further, exchange the boundary conditions of ports and E-field, it means different polarization direction of the metamaterial unit. More details, you can see the paper : Electromagnetic parameter retrieval from inhomogeneous metamaterials.
The boundary conditions are specific because of the structure of metamaterial unit cell. If you study about DNG materials, you will find that the electric field needs to be parallel to the rod/strip in your design and the magnetic field makes a loop around it or is in the direction of the loop, the direction of waveport will be transverse to both E and H fields. These are the basic conditions. You may read papers by Sir J.B.Pendry or Dr.D.R.Smith for this.
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