This video is taken from the FDTD Learning Track on Ansys Innovation Courses.
Using the associated script file, we have set up a substrate with a single spherical
particle with a diameter of 155 nm.
This particle will represent a defect on the structure and we'll calculate the scattered
field profile in the far field due to the defect.
A mesh override region has been placed around the scattering particle and a power monitor
has been added above the structure to collect the reflected scattered fields from the particle.
This monitor should be located in the scattered field region after the source is added.
Add the TFSF source from the sources drop down menu.
Edit the source using the edit button in the side toolbar or the E keyboard shortcut.
In the General tab set the injection axis to z-axis and direction to backward to inject
the source from above the structure towards the negative z-direction.
In the Geometry tab, set the x, y, and z spans of the source to 0.3 um.
This sets the size of the total field region of the source.
Make sure that the x and y position of the source is centered at 0 and set the z position
to 0.1 um.
In the Frequency/Wavelength tab, set the wavelength of the source to 0.63 um, and click OK to
accept the settings.
Before running the simulation, check to make sure that boundaries of the source do not
intersect with monitor or the scattering particle, and the edges of the source pass through the
Now, click run.
After the simulation is complete, I can right-click and visualize the farfield result from the
monitor to see the angular distribution of the scattered fields.
Next, we'll go over some setup tips for the total-field scattered-field source.
As we saw in the demonstration, a mesh override region was used, and it covered the full volume
of the total field region of the source.
Using a uniform mesh step size in the directions normal to the injection axis over the source
volume ensures that the subtraction operation at the source boundaries is as accurate as
This can be particularly important when injecting the source at a non-normal incident angle.
You can test the setup by temporarily disabling the particle or defect and run the simulation
to determine the noise floor in the scattered field region.
Ideally if there is no noise the magnitude of the electric field in the scattered field
region should be 0.
The total-field scattered-field source should never be extended through PML or metal boundary
conditions, but they can be extended through periodic or Bloch boundaries if simulating
If there is a substrate, the injection axis of the source should be normal to the substrate.
The side edges of the source are used to determine what fields get subtracted at the boundaries
so they should pass through the substrate but not intersect with scattering structures.
It's also possible to obtain the scattered fields without using the total-field scattered-field
source by running two separate simulations one without the scattering feature to get
the reference fields, and one with the scattering feature.
The scattered fields can be calculated by subtracting the reference fields from the
fields in the case with the scattering feature.
This method is useful if you want to get the scattered fields due to a source with a different
field profile instead of a plane wave.
See the Custom TFSF example linked below for more details.