The mesh order property governs how overlapping objects are meshed in the simulation. It serves no role for objects which do not overlap. The mesh order can be set at the material level (in the material database), or the object level (in the object properties). Materials with a lower mesh order take priority over materials with a higher priority number (i.e. order 1 takes priority over 2). Areas that overlap are assigned the material properties of the higher priority material (see the following figure).
In the figure above, there are two objects that partially overlap. Depending on their mesh orders, the object that is actually being simulated will be different. In the event that both overlapping materials have the same order, the mesh order will be inferred from the Object tree. Objects at the bottom of the tree will 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, one can use setmaterial (material level), setnamed, or set (object level).
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Mesh order in FDTD and MODE
- 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.
The etch material in the default Material database: 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.
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. For example, 3d cylinder overlapping a 2d rectangle will not create a hole in the 2d rectangle, regardless of their mesh order.
- To create a hole in a 2d material, you can use 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 CHARGE, HEAT, DGTD, FEEM
- Plot the device geometry after meshing to confirm that the structures were meshed as intended. The ID plot displays the geometry of your design based on several factors, such as the mesh order, sequence that the objects are created, and the material of the objects. To show the ID, hit the "Recalculate simulation mesh" button to calculate mesh, then right-click on "Device region" and "visualize" grid. A visualizer should pop up, then select "ID" in the Attribute drop-down list.
IDs of connected and split objects: If two objects are overlapped/connected and they are made of the same material, these two objects will be considered as a whole and thus share the same ID. If one object is fragmented into pieces by the insertion of another object, these fragments will be considered as individual objects and thus have different IDs.