Cylinders

[GenB31415]

Hi @flaport,
I have to add a cylinder aligned || z in 3D.
There are various references in general how to create a cylinder.
https://stackoverflow.com/questions/26989131/add-cylinder-to-plot
https://stackoverflow.com/questions/64725784/color-of-the-cylinder-in-python

But what may be the optimal way to do that in fdtd?
[03-objects-of-arbitrary-shape]
Thank you in advance.

[Alex Izvorski]

@GenB31415 I think you can modify the 03-objects-of-arbitrary-shape example into 3d to make the circle into a cylinder, like this:

grid = fdtd.Grid(shape = (300, 300, 100), ...)
...
refractive_index = 1.7
x = y = np.linspace(-1,1,100)
X, Y = np.meshgrid(x, y)
circle_mask = X**2 + Y**2 < 1
permittivity = np.ones((100,100,10,3)) + circle_mask[:,:,None,None]*(refractive_index**2 - 1)
grid[170:270, 100:200, 45:55] = fdtd.Object(permittivity=permittivity, name="object")

That should give a z-axis aligned cylinder with diameter 100 and height 10. There's nothing really special about a cylinder, it's just a stack of circles; the None,None adds two extra size-1 axes (one for z and one for anisotropic permittivity), and numpy broadcasting makes a stack of the circle_mask along the extra axes to match the (100,100,10,3) shape.

[Floris Laporte]

Indeed. stacking circles is the recommended way.

[GenB31415]

Hi @aizvorski @flaport
Many thanks, this works. Is it possible by similar manner to create the the walled empty cylinder with the internal r1 and external r2 radiuses respectively? Thanks again.

[Floris Laporte]

Ideally this would be done by creating two overlapping Objects, however overlapping objects is currently not really supported. Alternatively you can change the grid.inverse_permittivity array manually. First create the bigger cylinder directly into the grid.inverse_permittivity array, then create the smaller one.

[GenB31415]

Hi @flaport
I've followed your comments in the attached files. In addition, I expanded the task a little. I usually prefer to study a 3D system, so.

1. I have placed a cylinder with walls in the center.
2. To visualize the structure of the field by slices, I use the well-known standard approach, which allows us to move and view the slices of the field along the z-axis using the mouse wheel.
3. I also applied the simplest Monte Carlo technique to see the geometry of the field. To this end I use N = 1000 randomly distributed point sources, please see the attached figure, where is shown the field slice for z=50.
   Thanks for the comments.
   circular_object00e.zip
   

[GenB31415]

Sorry, the number of sources is N=55 (not 1000)

[Floris Laporte]

Hey @GenB31415 , this looks cool! Can you add this to the examples folder and create a PR for this?