This video is taken from the FDTD Learning Track on Ansys Innovation Courses.
- Monitors - Movie (information about movie monitor and settings)
- Diverging Simulations (troubleshooting instructions for diverging simulations)
Movie monitors record fields over time and save them to a .mpg movie file that can be
played back with a video player software like Windows Media Player in Windows or VLC Media
The videos showing the time domain propagation from sources in the previous sources section
of the course were all generated using movie monitors.
The movie monitor basically works like a 2D time monitor taking snapshots of the fields
at different time steps and then putting together all the snapshots into a movie file.
Movie monitors always have a 2D geometry so the movie will show a slice of the fields
and you should place the monitor over the cross section that you want to slice.
You can choose the field component that you want the monitor to record, and while the
simulation runs, snapshots of the fields in time are saved to generate a .mpg file in
the current working directory.
The file name of the generated movie file will be filename_monitorname.mpg where filename
is the name of the simulation file, and monitorname is the name of the movie monitor.
This means that you should not have two monitors with the same name since they will conflict,
and it also means that when you re-run a simulation file without changing the file name or monitor
name, the existing movie file in the current working directory will be overwritten.
The resolution of the movie file and frame rate can be set by editing the monitor.
However, the fields calculated during the simulation are calculated on the simulation
mesh, so the fields will not look smoother in the final movie by increasing the resolution
used by the movie monitor if the simulation mesh is coarser than the movie resolution.
You can also choose to generate the movie with or without outlines that indicate the
positions of structure interfaces.
Using the structure outlines helps give some context to the positions of the fields in
the movie relative to the structures.
It’s also possible to scale the amplitude of the fields in the movie by editing the
But, using a scale that is too small will result in saturation of the movie, or a scale
that is too large will result in very faint radiation patterns that can’t be made out
A scale value between 0.1 and’ 1 usually works well, however, the movie monitor outputs
its maximum intensity after running the simulation in the variable called monitorname_maxI.
So if you find that the fields are saturated or too faint in your movie, setting the scale to
factor monitorname_maxI and rerunning the simulation will make sure that the fields
in the movie will not be saturated.
There is no colour bar to show the corresponding field intensities in the movie, so the movie
is meant to be used to get the general idea of how the fields are propagating over time
rather than for getting quantitative results or field values.
A movie of the time domain fields can give some intuition about how the device is working,
so it can be useful for troubleshooting or to illustrate how the device behaves.
It can also be used to debug a diverging simulation.
A diverging simulation is one which contains some numerical instability which causes the
field amplitudes to diverge towards infinity.
Common causes are instability are the PML boundary, or instability in a particular material
such as a material with gain.
By using a movie monitor you can see where the fields start to diverge.
You might see the fields start to saturate near the PML boundary which indicates a PML
instability, or from within a particular structure which would indicate a material instabiliy.
This can help you choose the method to use to fix the divergence and make the simulation
More details and an example can be found in the Diverging simulations page linked below