This video is taken from the FDTD Learning Track on Ansys Innovation Courses.
In the “Mesh settings” tab, you can choose between the auto non-uniform, custom non-uniform,
and uniform mesh types.
The auto non-uniform option is the default option and recommended for most simulations.
With this option, the mesh will automatically adapt based on the material properties, the
wavelength of interest and desired accuracy level.
The mesh accuracy slider can be set between 1-8 where 1 means that the mesh that is generated
will have at least 6 mesh points per wavelength, 2 means 10 points per wavelength and so on
up to 34 points per wavelength using mesh accuracy 8.
The mesh will be smaller in materials with a higher refractive index since the effective
wavelength in high index materials is smaller.
The "uniform" mesh option simply allows you to specify uniform mesh step size along each
The mesh can be specified either by specifying the number of mesh cells in that direction
or the maximum mesh steps size.
The "custom non-uniform" mesh provides some alternate options for controlling the mesh.
The automatic meshing option is much easier to use, and therefore these custom options
are rarely used.
The time step settings include dt and the dt stability factor.
The dt setting displays the time step.
The dt stability factor setting is a multiplier that can be applied to reduce the time step.
The default time step settings are typically sufficient, and using a smaller time step
would increase the amount of time that it takes to run the simulation since it would
mean that more steps need to be used.
However, in some cases, if the simulation is unstable, a smaller time step is required.
The minimum mesh step size is a setting which prevents an unreasonably small mesh step size
from being generated.
The mesh that is generated cannot have mesh step sizes below the limit set by the minimum
mesh step size setting.
This setting is here to prevent unreasonably small mesh sizes that can cause the software
to become slow or freeze.
This setting rarely needs to be modified, unless you are working at a much longer wavelength
and want to impose a larger minimize mesh size.
Finally, the mesh refinement method can also be set in the “Mesh settings” tab.
This setting controls how material interfaces are treated in the simulation.
This can be especially important when simulating structures with curved surfaces.
Since the mesh in FDTD Solutions is rectangular, curved surfaces or surfaces angled with respect
to the Cartesian axes will result in some mesh cells including multiple materials.
The simplest refinement option is stair casing, in which case the entire cell will be filled
with whichever material occupies most of the volume of the mesh cell.
However, using conformal meshing technology, it is possible to solve Maxwell’s integral
equations near structure boundaries to better represent the surface, effectively giving
some amount of subcell accuracy.
In other words, you can get similar accuracy using the conformal meshing method as you
would by using the stair casing method with a finer simulation mesh.
**Refer back to the FDTD algorithm section of the course if you’d like to review the
details about the conformal meshing method.
“Conformal variant 0” is the default mesh refinement option, which applies the conformal
meshing algorithm to all non-metal material interfaces.
It is worth noting that the conformal meshing algorithm is more complex than a simple weighted
average of the materials with the mesh cell volume.
To apply conformal meshing to interfaces that involve metals, use the "conformal variant
1" mesh refinement method.
However, the “conformal variant 1” mesh refinement method can lead to artificial modes
at the surfaces of metals, especially if the simulation mesh is too coarse.
Additional convergence testing will be required when using “conformal variant 1”.
Other mesh refinement options are available, but they are not as robust and are typically
only used if you are trying to reproduce published simulation results which used a particular
mesh refinement method.
The details about each of the available mesh refinement options are available in the related