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 > _______________________________________________ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
