Hello meep-users,
i have a question regarding point sources in meep. I have been working
with meep some time now and need it for the simulation of goniometric
measurements. As i did not get expected results, i stripped down my
problem until i got the following:
(set-param! dimensions 3)
(set! geometry-lattice (make lattice (size 10 10 10)))
(set! default-material (make dielectric (epsilon 1)))
(set! pml-layers (list (make pml (thickness 1))))
(set-param! resolution 10)
(set! sources (list
(make source
(src (make continuous-src (frequency 1)))
(component Ex)
(center 0 0 0))))
(run-until 10 (at-every 0.1
(with-prefix "yz-" (in-volume (volume (center 0 0 0) (size 0 10 10))
output-efield-x output-efield-y output-efield-z))
(with-prefix "xz-" (in-volume (volume (center 0 0 0) (size 10 0 10))
output-efield-x output-efield-y output-efield-z))
(with-prefix "xy-" (in-volume (volume (center 0 0 0) (size 10 10 0))
output-efield-x output-efield-y output-efield-z))
))
It is just an empty box with an electric point source in the center
radiating in x-direction. From theory i know that an oscillating current
source restricted to a point in x-direction (something like
diracDelta(x)*exp(i w t)*(1,0,0) ) generates spherical waves polarized
in x-direction, so only the Ex-component should get excited, while other
electrical components should not.
But meep-1.1.1 and 1.2 (did not test earlier) show strange behaviour in
this case:
* In the yz-plane containing the source, the expected behaviour can be seen.
* But in the xy-plane (also through the source), the Ex-component looks
like a separeted dipole having a vertically compressed wave pattern. Ez
even looks like quadro-pole excitation, while Ey is zero. But they
should be both zero - or i am missing someting?
* xz-plane looks the same except that Ey an Ez swap, and the compression
appears horizontally.
For me it looks like there is anisotropic epsilon, but this is clearly
not the case (i also checked the structureChunks, they all had
trivialEpsilon).
So is there something wrong with meep, or is there an error in my
assumptions?
Thanks for any suggestions!
Greetings from germany,
Roger John
PS:
I can provide the conversion script for the animations or the animated
gifs themselves if wanted (can i attach directly?).
_______________________________________________
meep-discuss mailing list
meep-discuss@ab-initio.mit.edu
http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
