The mesh order property governs how overlapping objects are meshed in the simulation. It serves no role for objects which do not overlap.
In FDTD and MODE, the mesh order of objects can be set at the material level in the material database, or at the object level in the Material tab of object properties. The mesh order set in the material database acts as the default values.
In Multiphysics, you can only set the mesh order through the Material tab.
Materials with a lower mesh order take priority over materials with a higher mesh order (i.e. order 1 takes priority over 2). Areas that overlap are assigned the material properties of the higher priority material in the simulated geometry as seen in the figure.
In the figure above, there are two objects that partially overlap. Depending on their mesh orders, the geometry that is simulated is different. If both overlapping materials have the same order, priority is inferred from the Object tree. Objects at the bottom of the tree take priority over objects at the top of the tree.
To ensure your simulation is well defined, it is recommended that you avoid situations where two different overlapping structures have the same mesh order. To set the mesh order using script, you can use setmaterial (material level), setnamed, or set (object level).
Alternative video source in Mandarin, click here
Mesh order in FDTD and MODE
- In FDTD and MODE, you can change the mesh order at the material level or object level. You can enable object level mesh order in the Material tab by turning on override mesh order from material database.
- The simulation grid in FDTD and MODE is determined from the bounding boxes of geometries, and not the mesh order. Therefore, where two materials overlap, the mesh will be refined for the material with higher refractive index, even if that is not the priority material according to mesh order.
- For simulations using the conformal mesh, the mesh order property defines the material properties in the mesh cells where materials fully overlap one another. In the mesh cells which contain boundaries between two materials, the conformal mesh algorithm solves Maxwell's integral equations near these boundaries.
- Use an index monitor to confirm that the structures are meshed as intended.
-
By default, most materials in the material database have a mesh order of 2. The only exception is the etch material, which has a mesh order of 1. The lower mesh order means that an object using the etch material will override other objects of a different material type, which effectively cuts a hole.
The etch material has a refractive index of n=1. If you are using a different background index, you should modify the etch material to match the background index of your simulation.
- 2D objects always take priority over 3D objects regardless of mesh order. For example, a 3D cylinder overlapping a 2D rectangle will never create a hole in the 2D rectangle.
- To create a hole in a 2D material, you must define the hole yourself in the script. An example is shown in the script file, [[2d_poly_examples.lsf]], in the 2D polygon page.
- 2D objects respect mesh order among themselves. For example, a 2D rectangle with RLC overlapping a 2D polygon with PEC. The material of the overlap is determined according to mesh order.
Mesh order in Multiphysics (CHARGE, HEAT, FEEM, DGTD)
- In Multiphysics, you can only modify the mesh order through the Material tab in each geometry object. You cannot assign an order for a material.
- The preserve surface option allows you to avoid the merging of domains between objects, giving you the freedom on how domains are formed when there is an overlap. For an example see Preserve Surfaces in the Reference geometry Knowledge base article.
- To check the simulated geometry of your device, you can use the partitioned volume mode. In this mode, you can view the simulation with separate domains and confirm that overlapping geometries use the material you intend.