STL import - Simulation object

FDTD MODE

STL_import_GUI.JPGSTL (Standard Tessellation Language or STereoLithography) is a well-supported format for many 3D CAD products. It is widely used for rapid prototyping and computer-aided manufacturing. STL files describe the surface geometry of 3D objects by triangular representation of the objects.  The surface of the objects are broken into a series of triangles. Each triangle is uniquely defined by its three vortices and the surface-normal vector.

STL files can be imported by selecting 'File' --> 'Import' --> 'STL'. Multiple STL objects, as shown below, can also be imported by sequentially importing each file. Once imported, the STL-imported objects are treated as planar solid objects in the layout editor.

The associated files below can be used to test the import. When imported, the assembly is recognized as a single object. Alternatively, each part can be separately imported and assembled in the layout editor. In this case, each part imported is treated as a separate object.

Notes:

  1. Binary and ASCII compatible:
    Both Binary and ASCII STL files are recognized in the layout editor. However, Binary files are recommended since they are smaller in size.
  2. Length unit:
    An STL file does not contain any information about the length unit used in the CAD software where you created the STL file. For example, a 30 (mm) x 30 (mm) x 30 (mm) cube in STL-format created in a CAD with a length unit set to mm will be recognized as 30 (um) x 30 (um) x 30 (um) in size by default, see stlimport to change the scaling factor. To avoid any size issues, it is recommended that you choose the right length unit in the layout editor prior to importing STL files.
  3. Material:
    An STL file can represent only one type of material. An STL-imported object cannot be subdivided into multiple pieces. Therefore, if  there are multiple shapes (or groups of shapes) that require separate material definitions, they should be created into different STL files.
  4. Tolerance: 
    STL files may be created with different levels of tolerance. A tight tolerance results in a large file with many surface facets. These files take a long time to load and display. A looser tolerance results in fewer surface facets. It is generally a good idea to start with a loose tolerance and increase it as necessary to achieve a balance between the file size and surface refinement.

Geometry tab

  • X, Y, Z: The relative position of imported object from the origin of the layout editor.

Material tab

The material options are as follows:

  • MATERIAL: This field can be set to any material included in the material database. It is possible to include new materials in the database, or edit the materials already included. See the material database section for more information.
  • OVERRIDE MESH ORDER FROM MATERIAL DATABASE: Select to override the mesh order from the material database and manually set a mesh order. The mesh order is used by the simulation engine to select which material to use when two materials overlap. See the mesh order (optical) or mesh order (electrical) section for more details.
  • MESH ORDER: Set the mesh order in this field if the OVERRIDE MESH ORDER FROM MATERIAL DATABASE option is selected. If the option is not selected, the field displays the material's default mesh order from the database. For example, a material of mesh order 1 will take precedence over a material of mesh order 2.

The following only applies to MODE and FDTD:

If <Object defined dielectric> is selected, then the INDEX property must be set.

  • INDEX: The refractive index of the structure, when the material type is <Object defined dielectric>. The index must be greater than one.
      • Anisotropic index: To specify an anisotropic refractive index, use a semicolon to separate the diagonal xx,yy,zz indices. Eg. 1;1.5;1
      • Spatially varying index: It is possible to specify a spatially varying refractive index by entering an equation of the variables x,y,z in this field. Eg. 2+0.1*x will create an object where the refractive index increases in the X direction. The units of the spatial variables (x,y,z) must be set with the 'INDEX UNITS' property described below. The variables x,y,z will be zero in the center of the object. When using an equation in this field, consider using a mesh override region to control the simulation mesh size. For more information on entering equations, see the Equation interpreter section.
  • INDEX UNITS: Only relevant when specifying a spatially varying equation in the INDEX properly described above. Specify the units (nm, um, m) of the x,y,z position variables.
  • GRID ATTRIBUTE NAME: Enter the name of the grid attribute that applies to this object, see the grid attribute section

The following only applies to CHARGE, HEAT, FEEM, DGTD:

If the material chosen from the drop down menu is a binary alloy consisting of two semiconductors, then there will be an additional property, namely, the "composition fraction" to set as well.

COMPOSITION FRACTION: This is x, the fraction of the semiconductor in the alloy. x can either take a fixed value or vary.

The user can see which semiconductor has fraction x and which has fraction (1-x) shown in a line above this drop down menu.

FIXED: This means that fraction x will be a constant value between 0 and 1.

LINEAR X/Y/Z: This means that the composition fraction x will vary as a function x or y or z. In this case, user can specify the min and max fraction values for the min and max spatial points and the fraction will be interpolated linearly in between. x,y,z here are those of the unrotated object. x,y,z are local to the object.

EQUATION: The user can enter an equation for the fraction that varies with u,v and w. u is (x-x0), v is (y-y0) and w is (z-z0) where x0, y0 and z0 are the center coordinates of the object. This means that u,v and w are local to the object.

Rotation tab

Rotate objects by setting the following variables:

  • FIRST, SECOND, THIRD AXES: Select rotation axis. Up to three different rotations can be applied.
  • ROTATION 1,2,3: The rotation of the object in a clockwise direction about each axis, measured in degrees.

Graphical Rendering tab

The graphical rendering tab is used to change how objects are drawn in the layout editor. The options are:

  • RENDER TYPE: The options for drawing the objects are detailed or wireframe. Detailed objects are shaded and their transparency can be set using OVERRIDE COLOR OPACITY FROM MATERIAL DATABASE.
  • DETAIL: This is a slider which takes values between 0 and 1. By default it is set to 0.5. Higher detail shows more detail, but increases the time required to draw objects. This setting has no effect on the simulation.
  • OVERRIDE COLOR OPACITY FROM MATERIAL DATABASE: When unselected the opacity is determined from the material database. When selected, you can specify a value for ALPHA between 0 (transparent) and 1 (opaque) for the object, depending on how transparent you want the object to be.

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