On Mon, 23 Apr 2007, celia wrote: > I set different k corresponding to the same frequency, and find some > phenomena I could not explain. One example is > http://ab-initio.mit.edu/wiki/index.php/Meep_Tutorial/Band_diagram% > 2C_resonant_modes%2C_and_transmission_in_a_holey_waveguide > In the third subsection(band diagram), I set fcen=0.3175 df=0.1 k=0.4 > and position the point source at (0.5,0), and achieve a guided mode > which is the same as in the example. > With other parameters unchanged, I set k=0.25 and get a leaky mode; I > set k=0.45 and get a guided mode. The output command is > (run-sources+ 400 > (at-beginning output-epsilon) > ) > (run-until (/ 1 fcen) (at-every (/ 1 fcen 20) output-hfield-z)) > > Pay attention that the points (k=0.25,w=0.3175) (k=0.45, w=0.3175) > are not in the band curve. Before the simulation, I have thought those > points should not correspond to a leaky/guided/extended mode. Then what > is wrong about my view?
First, what do you mean when you say that you "find a mode"? You are not running harminv, you are just exciting the fields with a pulse source. Of course you will get *some* fields, regardless of whether there is an eigenmode nearby. What you will tend to see, after running a long time, will be the guided mode or leaky mode that is excited with the largest amplitude and/or has the longest lifetime. Second, notice that you are putting in a pulse with a fairly broad bandwidth, and there are severl guided/leaky modes nearby that you might be exciting. For example, at k=0.45, there is an guided mode at a frequency close to 0.3, so you will clearly excite this strongly. Cordially, Steven G. Johnson _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
