Hi Filip,
Thanks for your response. This is how the run is carried out:
(run-sources+
(stop-when-fields-decayed
50
Ez
(vector3 0 0 (- 0 z_plane_src))
1.0e3
)
)
It looks to me as if the simulation ends as soon as the pulse ends, and the
actual duration of the simulation is the same in the two cases (with and
without the antenna). This is what the output shows at the end:
...
on time step 1997 (time=49.925), 3.06965 s/step
on time step 1999 (time=49.975), 3.04618 s/step
field decay(t = 50.025): 0.00198287709153593 / 0.00198287709153593 = 1.0
run 0 finished at t = 50.025 (2001 timesteps)
creating output file "./metal-reflected-flux.h5"...
Since there is only the simple metal scatterer, with absorbing boundaries all
around, I do not believe there are any resonances.
________________________________________
From: Filip Dominec [filip.domi...@gmail.com]
Sent: Wednesday, 11 February 2015 10:49 a.m.
To: Gib Bogle
Cc: meep-discuss@ab-initio.mit.edu
Subject: Re: [Meep-discuss] Puzzling results for reflection spectrum
Hi, if you properly divide the reflected amplitude by the incident
amplitude, the reflection of a linear system should indeed be the
same, independent of the source duration and spectrum.
If it is not, one possible cause may be that you clip the time record
while the source was still running, or the structure was still
retaining some energy in resonances. What happens if you run the
simulation for 2x and 3x longer time?
Filip
2015-02-10 22:30 GMT+01:00, Gib Bogle <g.bo...@auckland.ac.nz>:
> I am getting puzzling inconsistencies between results for the reflection
> spectrum of a scatterer when I vary the width of the Gaussian pulse. Since
> I am a beginner this probably stems from my lack of understanding of
> something.
>
> The scattering antenna is a metal loop with a small gap (i.e. the loop is
> not closed). The conductor cross-section is rectangular, 0.2 wide and 0.1
> thick (all Meep units). The inner radius is 0.868, and the gap is 0.2. The
> antenna lies in the xy plane, centred at the origin.
>
> The region size is 4p x 4p x 6p, where p=6, and the PML thickness is p. The
> plane wave source is located at the lower edge of the PML, i.e. at z = -2p,
> and the flux plane is at z = -p, halfway between the wave source and the
> antenna. The frequency I am interested in is 5.5 GHz, i.e. a Meep frequency
> of 0.1833 with a Meep unit distance of 0.01m. This corresponds to a Meep
> wavelength of 5.456, which explains why I am using p=6.
>
> I am using resolution=20. The Gaussian pulse that is exciting the
> reflection has a centre frequency of 0.1833, and I have simulated various
> pulse widths, always with nfreq=100. With df=0.1 the reflection spectrum
> has a well-defined minimum at (0.139, 1.3E-06), and a flat local minimum at
> (0.181, 8.35E-6). With df=0.2 there is just a very flat minimum at (0.178,
> 1.97E-6), and with df=0.3 a minimum at (0.1, 1.61E-6). Zooming in with
> df=0.05 shows just the local minimum at (0.183, 8.4E-6), more like a point
> of inflection.
>
> Are these results surprising? Am I making an obvious mistake? I would be
> grateful for guidance.
>
> Thanks
> Gib
>
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