Dear Steve, 1) Use the value of 2.3. The static permittivity is invariant to scaling.
2) If you wanted to model realistic copper, with scaling of 1:1e6, you would have to feed MEEP with values normalized to the scaling (1e6) and also by the speed of light (2.998e8). For instance, the physical Lorentz oscillator frequencies would have to be divided by 2.998e14 in your scripts, if you intended to exactly model some dielectric [such as http://fzu.cz/~dominecf/misc/eps/]. However you can not do this in your case, as your microwave simulation would go unstable. I observed there is a FDTD critical frequency [see http://fzu.cz/~dominecf/meep/index.html#stability], above which the permittivity of all materials has to be positive. If you keep the Courant factor at the default value (0.5), and wish to model a cavity of 0.3 m length with, say one million voxels, your resolution would be 0.003 m and the critical frequency would be about 60 GHz. A metal model that approximately follows the Drude model with correct losses at low frequencies, and that has positive real part of permittivity at higher frequency than 60 GHz, has to be used. I will try to write about a reasonable method how to efficiently define lossy metals for a stable FDTD simulation, on the above mentioned website in the next days. 3) The 50 um thin wall you wrote about is a related topic. I believe you do not wish to use 50 um resolution for a 300 000 um-sized simulation volume in FDTD. One option is to use FEM or other Maxwell-solving method instead, the second one is to define a thin layer of another "effective metal", whose conductivity is appropriately reduced by the ratio of the pixel size to the 50 um thickness. So if you use a voxel size of 3000 um, and so is the thickness of the wall, you define the conductivity as 60 times lower than that of bulk copper. I got very reasonable results when simulating thin metallic layers in MEEP. Of course, all such simulations should be quantitatively verified. 4) Sorry, I can not help with symmetries, in MEEP they never worked for me as I expected. 5) Nor did I use the cylindrical coordinates. Hope this helps anyway. In few days (weeks) these mails should be also approved to appear in the mailing list. Filip 2014-11-23 19:31 GMT+01:00, Steve <russell7...@roadrunner.com>: > Dear Steven and Meep users, > > It has been several days since I have been able to post. Issues have > accumulated. > > 1 - In my Meep model I am using a dielectric resonator made of > Polyethylene, > PE. High density PE has a dielectric constant = 2.3. across a broad > range of frequencies. Do I use this value as the value of epsilon, as > in > (material (make dielectric (epsilon 2.3))) ? > Or does it need to be scaled somehow into Meep units? If so, How is it > scaled? > > 2 - I am using Copper, courtesy of Aaron Webster - > http://fzu.cz/~dominecf/meep/data/meep-metals.pdf. The data > Normalization length=1e-06 in meter. What does that mean to me > specifically with respect to my lattice size and resolution? Also see 3, > below. > > 3 - I am modeling a closed truncated copper cone resonator with very > thin copper ends. A 2-D model. The general dimensions of the cone are > 0.10 to 0.30 meter, the end thicknesses are 5e-5 meters and the drive > frequency is 2 GHz. For low resolution h5topng does not show the ends > but for high resolution (400) Meep does not execute succesfully for > lattice sizes large enough to contain the device. I would like to use > meep length a=1e-6 but that seems unapproachable. What am I missing in > my understanding of scaling, lattice size and resolution? > > 4 - I have tried to use symmetry to speed the calculations. It does, but > my cone does not maintain its shape. That is, this code > > ;(set! symmetries (list ; > *********Symmetry***** > ; (make rotate4-sym (direction 1) (phase (if xodd? -1 +1))) > ; (make rotate2-sym (direction 2)) > ; (make rotate4-sym (direction 1) ) ; (phase -1) defaults > to +1 > ; )) > > in all cases results in an h5topng image of my cone cut in the y-z plane > with one end reversed and joined to the same end. Is this a Bug or again > just my flawed understanding of the workings of symmetry in meep? > > 5 - I can run my model using cylindrical coordinates which speeds the > calculations tremendously but I don't understand how to generate 2-D > images for presentation. Is it possible? How? > > I hope this wish-list doesn't "turn you off." I will continue to search > for answers and hope for answers to these questions, most likely one/two > at at time. > > Thank you for your consideration and help. > > Stephen Russell > > > > _______________________________________________ > meep-discuss mailing list > meep-discuss@ab-initio.mit.edu > http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss > _______________________________________________ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
