Eigen-frequency analysis of metal grating

Dear all,

For a metal grating (see attached Structure_Reference.jpg), now I would like to analysis the dispersion relationship of surface plasmon wave supported by a metal grating, which propagates along the surface of the grating.

I choose Eigen-frequency analysis method:

I set left-right boundary as periodic boundary condition with Floquet periodicity (the related setting as well as other boundary conditions see Structure. JPG);

Here giving an example, when alpha is set as 80 degree, then the related eigenfrequency of surface plasmon mode is analyzed, the corresponding field distributions are see attached (a.jpg and b.jpg).

From the distributions, we can see that they are indeed the surface plasmon wave supported by the structure.

Then the dispersion relationship can be obtained simply based on these eigenfrequency values.

Above is my thought about the model.

Is it reasonable? If not, anybody could give me some suggestions?

Million thanks!