Zero thickness for volumetric equivalence of 2D material

Different subclass for volumeric equivalence of Medium2D

Filter out zero coefficient poles in volumetric equivalent with zero size 2d materials: there is no need to perform intersections with previously added 2d materials in _volumetric_structures_grid

tests/test_components/test_grid_spec.py

@@ -116,9 +116,7 @@ def test_autogrid_2dmaterials():
     )
     assert np.isclose(sim.volumetric_structures[0].geometry.bounding_box.center[2], 1, rtol=RTOL)
     grid_dl = sim.discretize(box.geometry).sizes.z[0]
-    assert np.isclose(
-        sim.volumetric_structures[0].geometry.bounding_box.size[2], grid_dl, rtol=RTOL
-    )
+    assert np.isclose(sim.volumetric_structures[0].geometry.bounding_box.size[2], 0, rtol=RTOL)
 
     # now if we increase conductivity, the in-plane grid size should decrease
     sigma2 = 4.5

tests/test_components/test_simulation.py

@@ -2003,10 +2003,10 @@ def test_sim_volumetric_structures(log_capture, tmp_path):  # noqa F811
         )
         if isinstance(struct.geometry, td.Box):
             assert np.isclose(
-                sim.volumetric_structures[0].geometry.bounding_box.size[2], grid_dl, rtol=RTOL
+                sim.volumetric_structures[0].geometry.bounding_box.size[2], 0, rtol=RTOL
             )
         else:
-            assert np.isclose(sim.volumetric_structures[0].geometry.length_axis, grid_dl, rtol=RTOL)
+            assert np.isclose(sim.volumetric_structures[0].geometry.length_axis, 0, rtol=RTOL)
         assert np.isclose(
             sim.volumetric_structures[0].medium.xx.to_medium().conductivity,
             sigma * thickness / grid_dl,

tidy3d/components/medium.py

@@ -4477,6 +4477,12 @@ def sel_inside(self, bounds: Bound):
         return self.updated_copy(**dict(zip(["xx", "yy", "zz"], new_comps)))
 
 
+class AnisotropicMediumFromMedium2D(AnisotropicMedium):
+    """The same as ``AnisotropoicMeidum``, but converted from Medium2D.
+    (This class is for internal use only)
+    """
+
+
 class FullyAnisotropicMedium(AbstractMedium):
     """Fully anisotropic medium including all 9 components of the permittivity and conductivity
     tensors.
@@ -5358,7 +5364,7 @@ def _weighted_avg(
                 return med
             else:
                 raise ValidationError("Invalid medium type for the components of 'Medium2D'.")
-            poles += [(a, weight * c) for (a, c) in pole_res.poles]
+            poles += [(a, weight * c) for (a, c) in pole_res.poles if c != 0.0]
         return PoleResidue(eps_inf=np.real(eps_inf), poles=poles)
 
     def volumetric_equivalent(
@@ -5430,7 +5436,9 @@ def get_background(comp: Axis) -> PoleResidue:
             ax_coord=media_bg[axis], plane_coords=media_fg_weighted, axis=axis
         )
         media_3d_kwargs = {dim + dim: medium for dim, medium in zip("xyz", media_3d)}
-        return AnisotropicMedium(**media_3d_kwargs, frequency_range=self.frequency_range)
+        return AnisotropicMediumFromMedium2D(
+            **media_3d_kwargs, frequency_range=self.frequency_range
+        )
 
     def to_anisotropic_medium(self, axis: Axis, thickness: float) -> AnisotropicMedium:
         """Generate a 3D :class:`.AnisotropicMedium` equivalent of a given thickness.
@@ -5667,7 +5675,7 @@ def is_comp_pec_2d(self, comp: Axis, axis: Axis):
 
 # types of mediums that can be used in Simulation and Structures
 
-MediumType = Union[MediumType3D, Medium2D]
+MediumType = Union[MediumType3D, Medium2D, AnisotropicMediumFromMedium2D]
 
 
 # Utility function

tidy3d/components/simulation.py

@@ -18,7 +18,7 @@
 from .geometry.base import Geometry, Box
 from .geometry.mesh import TriangleMesh
 from .geometry.utils import flatten_groups, traverse_geometries
-from .geometry.utils_2d import get_bounds, increment_float, set_bounds, get_thickened_geom
+from .geometry.utils_2d import get_bounds, set_bounds, get_thickened_geom
 from .geometry.utils_2d import subdivide, snap_coordinate_to_grid
 from .types import Ax, FreqBound, Axis, annotate_type, InterpMethod, Symmetry
 from .types import Literal, TYPE_TAG_STR
@@ -1245,7 +1245,6 @@ def snap_to_grid(geom: Geometry, axis: Axis) -> Geometry:
             avg_axis_dl = get_dls(geometry, axis, 1)[0]
             subdivided_geometries = subdivide(geometry, axis, avg_axis_dl, background_structures)
             # Create and add volumetric equivalents
-            background_structures_temp = []
             for subdivided_geometry in subdivided_geometries:
                 # Snap to the grid and create volumetric equivalent
                 snapped_geometry = snap_to_grid(subdivided_geometry[0], axis)
@@ -1258,21 +1257,11 @@ def snap_to_grid(geom: Geometry, axis: Axis) -> Geometry:
                     axis=axis, adjacent_media=adjacent_media, adjacent_dls=dls
                 )
 
-                new_bounds = (snapped_center - dls[0] / 2, snapped_center + dls[1] / 2)
-                temp_geometry = set_bounds(snapped_geometry, bounds=new_bounds, axis=axis)
-                temp_structure = structure.updated_copy(geometry=temp_geometry, medium=new_medium)
-
-                if structure.medium.is_pec:
-                    pec_plus = increment_float(snapped_center, 1.0)
-                    pec_minus = increment_float(snapped_center, -1.0)
-                    new_bounds = (pec_minus, pec_plus)
+                new_bounds = (snapped_center, snapped_center)
                 new_geometry = set_bounds(snapped_geometry, bounds=new_bounds, axis=axis)
                 new_structure = structure.updated_copy(geometry=new_geometry, medium=new_medium)
 
                 new_structures.append(new_structure)
-                background_structures_temp.append(temp_structure)
-
-            background_structures += background_structures_temp
 
         return tuple(new_structures)