# [Getdp] Floquet BCs

**Danny Holstein**
dgholstein at embarqmail.com

*Sun Nov 23 14:48:52 CET 2014*

All,
Does GetDP support Floquet BCs for periodic structures? I'd like to apply this to EM fields in traveling wave tubes such as helix and coupled cavity structures, etcetera. I don't see why Floquet conditions wouldn't be similarly applicable to other wave propagation in periodic structures, such as phonons in a crystal.
Of course, there is the separate issue of whether GMSH supports the generation of such a mesh, though I'm sure it wouldn't be a complicated workaround. The 2D mesh at the origin would have to match the mesh at the periodic boundary but with all the nodes translated by that period.
Let's say the periodicity is in Z, if we define one 2D mesh at Z = 0, and the same mesh at Z = L (same node and element numbers), then the element calculations just to the one side of L would have to do the calculations with translated values of Z (and, of course, the phase-shifted values from the surface mesh).
Regards,
Dan
BTW: An alternative is to include several periods of the structure and identify the eigenstates. Computation times are horribly longer and this solution doesn't provide a continuum to DC (or omega -> 0).
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