# Local Mesh Refinement

Local Mesh Refinement defines a local region that influences mesh generation without adding a physical structure to the model.

The Grid Size and Number of Grid choices correspond to tidy3d.MeshOverrideStructure (opens new window). The Medium choice uses a medium-bearing structure as a grid override.

Local mesh refinement is commonly used to refine conductors, dielectric gaps, feeds, ports, and regions with strong field variation.

# Name

name: Unique name for the override structure.

  • Required field

# Geometry

Specification of the override region.

# Center + Size

Object definition through a center position and size.

center: Center of the override region in x, y, and z-directions.

  • Type: floating-point number
  • Unit: m, mm (default unit), um

size: Size of the override region in x, y, and z-directions.

  • Type: floating-point number
  • Unit: m, mm (default unit), um
  • Constraint: greater than or equal to 0
  • Required field

# Bounds

Object definition through minimum and maximum coordinate bounds.

min: Values of the x, y, and z coordinates defining the lower corner of the override region.

  • Type: floating-point number
  • Unit: m, mm (default unit), um
  • Required field

max: Values of the x, y, and z coordinates defining the upper corner of the override region.

  • Type: floating-point number
  • Unit: m, mm (default unit), um
  • Required field

# Override Type

override_type: Method used to define the mesh override.

  • Options: Grid Size/Number of Grid/Medium
  • Required field

Local mesh refinement methods

# Grid Size

Select Grid Size to enter an absolute maximum grid step along each axis.

dl: Maximum grid size along x, y, and z-directions inside the override region.

  • GUI label: Grid Size
  • Type: three optional floating-point numbers
  • Unit: m, mm (default unit), um
  • Constraint: greater than 0 when specified
  • Default: None for each axis

NOTE

If one direction in dl is empty or set to None, Grid Size does not refine that direction. Grid-size overrides add shared grid planes along each axis, so the planes can extend outside the override box.

Grid size mesh override

# Number of Grid

Select Number of Grid to set the minimum number of grid steps that span the override region along each axis.

min_steps_per_size: Minimum number of grid steps across the override region in the x-, y-, and z-directions.

  • GUI label: Number of Grid
  • Type: three optional floating-point numbers
  • Unit: unitless
  • Constraint: greater than 0 when specified
  • Default: None for each axis

For a finite, nonzero override-region size, the target grid step along an axis is:

target grid step = override-region size / min_steps_per_size

NOTE

If one direction in min_steps_per_size is empty or set to None, Number of Grid does not refine that direction. The value is ignored when the override-region size is 0 or infinite along that axis.

When both dl and min_steps_per_size are set through the API, the automatic mesher uses the finer grid requested by the two values.

Number of Grid mesh override

# Medium

Select Medium to choose a material that guides automatic mesh resolution inside the override region.

medium: Medium used by the automatic mesher in the override region.

  • GUI label: Medium
  • Type: Medium
  • Required field when Medium is selected

NOTE

The selected medium is assigned to a structure in the grid override collection. It influences grid generation but does not add a physical structure to the simulation. Material properties such as higher permittivity can request denser automatic grid spacing.

Medium mesh override

# Advanced

These settings are available when Grid Size or Number of Grid is selected. They are not displayed for Medium.

enforce: Toggle whether the override is enforced even where another structure would request a smaller grid size.

  • Options:
    • True: Enforce the override inside the override region.
    • False: Allow finer grid requests to take precedence.
  • Default: False

shadow: Toggle how overlapping override structures are prioritized.

  • Options:
    • True: In overlapping regions, the later override structure can shadow earlier override structures.
    • False: In overlapping regions, use the smaller grid size.
  • Default: True

drop_outside_sim: Toggle whether portions outside the simulation domain are ignored.

  • Options:
    • True: Drop portions of the override region outside the simulation domain.
    • False: Apply the override where its projection overlaps the simulation domain.
  • Default: True

NOTE

Mesh override structures are used by grid generation when at least one grid direction uses AutoGrid or QuasiUniformGrid.

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