Mesh override regions can be used in conjunction with the auto non-uniform or custom non-uniform
mesh to specify a finer mesh over a particular region, object or a set of objects like we
saw in the introduction.
The mesh override is useful for specifying a finer mesh than the automatically generated
This can be important for accurately resolving the shape of small features of the structure
such as thin layers of materials or gaps.
It is recommended that to accurately resolve the thickness, at least 2 mesh cells should
be included over the thickness of a layer.
It can also be important for plasmonic devices where the results are sensitive to the meshing
so a fine mesh must be used at interfaces between metal and dielectric materials since
fields can be concentrated at the surface.
Using a fine mesh only where it is required is far more memory efficient that making the
mesh small throughout the entire simulation volume.
The mesh step size that is set by the mesh override region can be set by specifying the
maximum mesh step size in each direction, dx, dy, or dz.
Alternately, the set “equivalent index” option allows you to specify an equivalent
refractive index for the volume.
The automatic meshing algorithm will then generate a mesh appropriate for the specified
You can also choose which directions to override the mesh, so for example if you want to use
a finer mesh to resolve the thickness of a layer, you only need to override the mesh
step size in the direction of the thickness of the layer.
As with the maximum mesh step size setting in the “Mesh settings” tab of the solver
region, the mesh override region will attempt to set up a mesh with an integer number of
mesh cells over the span of the mesh override region, so if the span of the mesh override
region is not integer divisible by the specified dx, dy, or dz setting then the mesh step size
that is used may be rounded down so that the mesh override region will include an integer
number of mesh cells.
The geometry of the mesh override region can be specified directly, or you can use the
“based on a structure” option to specify the name of an object or structure group that
you want the mesh override settings to apply to.
If you specify the name of an object and there are multiple objects with the same name, the
mesh settings will apply to all of the objects with that name.
If you specify the name of a structure group, the mesh override settings will apply to the
full span of the area including the objects in the structure group as illustrated here.