I want to simulate a discrete random media with FDTD method.
the simulation environment is air that is filled with random spherical particles (that are small to the wavelength) with defined size distribution.
what is an efficient and simple way to create random scatterers in large numbers in FDTD code?
i have put some random scatterers in small area but i have problem producing scatterers in large numbers.
any tips, experiences and suggestions would be appreciated.
thanks in advance.
Are the scatterers dilute or densely packed? Is this your own FDTD code or commercial software? Are you skilled at programming?
If the scatterers are dilute, just write a script to create a few spheres at random points, being sure they are not accidentally overlapping. If the scatters are densely packed, you are going to need a simple particle simulation to stack the particles randomly without overlapping.
A great tool for this sort of thing is Blender. You can run a particle simulation to distribute particles in any way, export the particles as an STL file, and then import that into your FDTD software. My team has done this. It is simple and works very well. Blender is a great tool and open-source.
https://www.blender.org/
hi prof. Raymond Rumpf.
Thank you very much for your attention and for helpful guidances as always!
i want to simulate both case (dilute or densely packed).
i have written my own FDTD code and as i spent much of my times in learning and programming this numerical method (FDTD) now can say i'm skilled at programming FDTD.
i have written my FDTD code for dilute scatterers by the method you have suggested. and also have seen Blender that was really a great tool.
but still two questions remain for me. i'm appreciated having your helpful suggestions.
1) for large number of dilute or densely packed scatterers, should i parallelize my FDTD code to saw and obtain their multiple scatterings?
2) is it possible to import STL file from Blender, and then import that into MATLAB domain? (since i wrote my FDTD code in MATLAB)
thanks
Paralellizing a code is not easy. You may want to get a hold of a commercial tool like Lumerical or an open-source tool like Meep if you need parallelization.
It is possible. You will need to "voxelize" the STL file in order to identify points on the grid that are inside or outside of your particles. Search Mathworks website for anything called Voxelize or something like that. There is a little more information about this in Lecture 19 here:
http://emlab.utep.edu/ee5390em21.htm
Thank you Raymond Rumpf
I found your answer very helpful. May i know is there any way to restrict random particle/etches in shape such as spiral or helix?
Thanks
Are you asking how to make your particles a helix/spiral shape? First, before doing that, I recommend running simulations that will just use the effective properties that your helices should give. That will let you explore device ideas without needed the complexity and inefficiency of having to resolve the spirals in your grid. Second, you will want to create a small simulation of a helix to retrieve the effective properties. This is usually called homogenization or parameter retrieval. Third, if you need to, move on to your more complicated 3D simulation.
That still leaves the question of how to build a helix in a 3D grid. One way you can do this is to create the helix in a CAD software such as SolidWorks or Blender. You can export that model as an STL file, which is just a surface mesh that MATLAB (or whatever software you are using) can import. From there, there are codes available that can import those STL files and "voxelize" them into a 3D array. If you are using MATLAB, search the MathWorks website for "voxelize" and you will find multiple solutions. Once you have that, you can create copies of the spiral in your FDTD grid. This approach will let you import even more complicated shapes relatively easily. Alternatively, you can create the spiral directly in your grid. I would do this by creating a array that has a list of points along the center of your spiral. From there, you can calculate what points your FDTD grid should be assigned to that spiral by calculating their distance to the points on the spiral. If they are within a certain distance, assign the material properties of your spiral. Otherwise, assign the material properties of whatever medium the spirals are residing in.
I am sure there are plenty of other ways to do this. If you are interested, I dedicated almost all of Chapter 1 to describing techniques for building geometries into arrays for simulation using the finite-difference method. I do not specifcally talk about spirals, but you may find some of that chapter very helpful. Here is a link to the book website:
https://empossible.net/fdfdbook/
Hope this helps!!
Raymond Rumpf Thank you for suggestions and diffrent ways to draw the shape. For now I used FDTD software script to design structure then using shape vertices i can etch holes with some random pattern.
Thank you for recommending the book. It seems very helpful, i will try to get it.
I have another query related to analytical and FDTD solution in softwares. Let me know if I should post it as separate question.
I want to compare FDTD farfield solution i generated for reflective diffration from numerical solution with the analytical solution. Is it possible to find reflection diffraction program which i can modify as per my configuration.
Thank you!!
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