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flex_rf.tidy3d.Structure

Type: class │ Base(s): AbstractStructure

Description

Section titled “Description”

Defines a physical object that interacts with the electromagnetic fields. A Structure is a combination of a material property (AbstractMedium) and a Geometry.

Notes

Section titled “Notes”

Structures can indeed be larger than the simulation domain in tidy3d. In such cases, tidy3d will automatically truncate the geometry that goes beyond the domain boundaries. For best results, structures that intersect with absorbing boundaries or simulation edges should extend all the way through. In many such cases, an “infinite” size inf can be used to define the size along that dimension.

Practical Advice

For example, a waveguide extending along x should use td.inf to ensure it passes fully through PML regions:

waveguide = Structure(
    geometry=Box(center=(0, 0, 0), size=(td.inf, 0.5, 0.22)),
    medium=Medium(permittivity=3.48**2),
)

Structures that terminate inside PML can cause evanescent fields at the interface to be amplified by the absorber, potentially leading to simulation divergence.

For uniform pixelated design regions (e.g. topology optimization), use the convenience method from_permittivity_array, which creates a Structure with a CustomMedium from a 3D numpy array of permittivity values and a geometry defining the region:

design_region = td.Box(center=(0, 0, 0), size=(2, 2, 0.22))
structure = Structure.from_permittivity_array(
    geometry=design_region, eps_data=eps_array
)

Example(s)

Section titled “Example(s)”
from tidy3d import Box, Medium
box = Box(center=(0,0,1), size=(2, 2, 2))
glass = Medium(permittivity=3.9)
struct = Structure(geometry=box, medium=glass, name='glass_box')

Parameters

Section titled “Parameters”
geometry [GeometryType]

Defines geometric properties of the structure.
medium [StructureMediumType]

Defines the electromagnetic properties of the structure’s medium.
name [str | None] = None

Optional name for the structure.
background_permittivity [float | None] = None

DEPRECATED: Use Structure.background_medium. Relative permittivity used for the background of this structure when performing shape optimization with autograd.
background_medium [StructureMediumType | None] = None

Medium used for the background of this structure when performing shape optimization with autograd. This is required when the structure is embedded in another structure as autograd will use the permittivity of the Simulation by default to compute the shape derivatives.
priority [int | None] = None

Priority of the structure applied in structure overlapping region. The material property in the overlapping region is dictated by the structure of higher priority. For structures of equal priority, the structure added later to the structure list takes precedence. When priority is None, the value is automatically assigned based on structure_priority_mode in the Simulation.

Attributes

Section titled “Attributes”
viz_spec [VisualizationSpec | None]

Methods

Section titled “Methods”
eps_comp(row: Axis, col: Axis, frequency: float, coords: Coords)

Single component of the complex-valued permittivity tensor as a function of frequency.
eps_diagonal(frequency: float, coords: Coords)

Main diagonal of the complex-valued permittivity tensor as a function of frequency.
from_permittivity_array(geometry: GeometryType, eps_data: np.ndarray, **kwargs: Any)

Create Structure with geometry and CustomMedium containing eps_data for The permittivity field. Extra keyword arguments are passed to td.Structure().
list_from_custom_medium(*, medium: AbstractCustomMedium, slab_bounds: tuple[float, float] | None = None, axis: int | None = None, frequency: float | None = None, threshold: float | None = None, foreground_medium: StructureMediumType | None = None, background_medium: StructureMediumType | None = None, pixel_exact: bool = False, boundary_step: float | None = None, smooth_sigma: float = 0.0, min_hole_area: float = 0.0, min_island_area: float = 0.0, name_prefix: str = 'design_polyslab')

Create structures from a thresholded 2D slice of a custom medium.
list_from_dataarray(*, data: SpatialDataArray, slab_bounds: tuple[float, float] | None = None, axis: int | None = None, threshold: float | None = None, foreground_medium: StructureMediumType | None = None, background_medium: StructureMediumType | None = None, pixel_exact: bool = False, boundary_step: float | None = None, smooth_sigma: float = 0.0, min_hole_area: float = 0.0, min_island_area: float = 0.0, name_prefix: str = 'design_polyslab')

Create structures from a permittivity data array.
to_gds(cell: gdstk.Cell, x: float | None = None, y: float | None = None, z: float | None = None, permittivity_threshold: NonNegativeFloat = 1, frequency: PositiveFloat = 0, gds_layer: NonNegativeInt = 0, gds_dtype: NonNegativeInt = 0, pixel_exact: bool = False)

Append a structure’s planar slice to a .gds cell.
to_gds_file(fname: PathLike, x: float | None = None, y: float | None = None, z: float | None = None, permittivity_threshold: NonNegativeFloat = 1, frequency: PositiveFloat = 0, gds_layer: NonNegativeInt = 0, gds_dtype: NonNegativeInt = 0, gds_cell_name: str = 'MAIN', pixel_exact: bool = False)

Export a structure’s planar slice to a .gds file.
to_gdstk(x: float | None = None, y: float | None = None, z: float | None = None, permittivity_threshold: NonNegativeFloat = 1, frequency: PositiveFloat = 0, gds_layer: NonNegativeInt = 0, gds_dtype: NonNegativeInt = 0, pixel_exact: bool = False)

Convert a structure’s planar slice to a .gds type polygon.

Machine-Readable Export

Section titled “Machine-Readable Export”