# [Getdp] Travelling Wave Boundary Conditions

**David Eimerl**
deimerl at eimexinc.com

*Fri Feb 15 22:28:30 CET 2013*

To GetDP Users/ FDTD Experts!:
I am setting up a vector electromagnetic wave problem with travelling wave
boundary conditions on the surfaces of a cube.
The E-field on the boundary is solution of the full vector Maxwell's
equations for a wave travelling in a general direction (i.e. not normal to
any cube surface)
The cube side is a few wavelengths.
I'm trying a FunctionSpace for Form1, with BF_Edge basis functions, and a
Galerkin resolution. The problems I run into include:
(a) Using a constraint with a TimeFunction that depends on the corrdinates
as well as $Time, does not compile.
(b) HarmonicToTime presumes the phase of the field on the boundary is
everywhere the same, so that it works for a standing wave i.e. for two
travelling waves, but not for a single travelling wave. This forces me to
use a Newmark scheme, I think.
(c) Adding time-dependent terms in NxH and following the MWE.pro examples
reproduces the HarmonicToTime result, (if I did it right).
(d) getDP seems to generate the resonant modes of the cube quite easily
with several different boundary conditions. However, a full complement of 3D
PML layers with R~0.001 does not remove this resonant behavior. In fact they
apparently has no effect.
Any suggestions? Or examples? Say from a general 3D waveguide problem?
DavidE
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