# Defines specifications for subpixel averaging
from __future__ import annotations
from typing import TYPE_CHECKING, Union
from pydantic import Field
from .base import Tidy3dBaseModel, cached_property
from .types.base import discriminated_union
if TYPE_CHECKING:
from tidy3d.compat import Self
# Default Courant number reduction rate in PEC conformal's scheme
DEFAULT_COURANT_REDUCTION_PEC_CONFORMAL = 0.3
# Default Courant number reduction rate in Surface impedance conformal's scheme
DEFAULT_COURANT_REDUCTION_SIBC_CONFORMAL = 0.0
[docs]
class AbstractSubpixelAveragingMethod(Tidy3dBaseModel):
"""Base class defining how to handle material assignment on structure interfaces."""
@cached_property
def courant_ratio(self) -> float:
"""The scaling ratio applied to Courant number so that the courant number
in the simulation is ``sim.courant * courant_ratio``.
"""
return 1.0
[docs]
class Staircasing(AbstractSubpixelAveragingMethod):
"""Apply staircasing scheme to material assignment of Yee grids on structure boundaries.
Note
----
For PEC interface, the algorithm is based on:
A. Taflove and S. C. Hagness, "Computational electromagnetics: the
finite-difference time-domain method", Chapter 10.3 (2005).
"""
[docs]
class PolarizedAveraging(AbstractSubpixelAveragingMethod):
"""Apply a polarized subpixel averaging method to dielectric boundaries, which
is a phenomenological approximation of :class:`.ContourPathAveraging`.
Note
----
The algorithm is based on:
A. Mohammadi, H. Nadgaran and M. Agio, "Contour-path effective
permittivities for the two-dimensional finite-difference
time-domain method", Optics express, 13(25), 10367-10381 (2005).
"""
[docs]
class ContourPathAveraging(AbstractSubpixelAveragingMethod):
"""Apply a contour-path subpixel averaging method to dielectric boundaries.
Note
----
The algorithm is based on:
A. Mohammadi, H. Nadgaran and M. Agio, "Contour-path effective
permittivities for the two-dimensional finite-difference
time-domain method", Optics express, 13(25), 10367-10381 (2005).
"""
DielectricSubpixelType = discriminated_union(
Union[Staircasing, PolarizedAveraging, ContourPathAveraging]
)
[docs]
class VolumetricAveraging(AbstractSubpixelAveragingMethod):
"""Apply volumetric averaging scheme to material properties of Yee grids on structure boundaries.
The material property is averaged in the volume surrounding the Yee grid.
"""
staircase_normal_component: bool = Field(
True,
title="Staircasing For Field Components Substantially Normal To Interface",
description="Volumetric averaging works accurately if the electric field component "
"is substantially tangential to the interface. If ``True``, apply volumetric averaging only "
"if the field component is largely tangential to the interface; if ``False``, apply volumetric "
"averaging regardless of how field component orients with the interface.",
)
MetalSubpixelType = discriminated_union(Union[Staircasing, VolumetricAveraging])
[docs]
class HeuristicPECStaircasing(AbstractSubpixelAveragingMethod):
"""Apply a variant of staircasing scheme to PEC boundaries: the electric field grid is set to PEC
if the field is substantially parallel to the interface.
"""
PECSubpixelType = discriminated_union(Union[Staircasing, HeuristicPECStaircasing, PECConformal])
PMCSubpixelType = discriminated_union(Union[Staircasing, HeuristicPECStaircasing])
[docs]
class SurfaceImpedance(PECConformal):
"""Apply 1st order (Leontovich) surface impedance boundary condition to
structure made of :class:`.LossyMetalMedium`.
"""
timestep_reduction: float = Field(
DEFAULT_COURANT_REDUCTION_SIBC_CONFORMAL,
title="Time Step Size Reduction Rate",
description="Reduction factor between 0 and 1 such that the simulation's time step size "
"is ``1 - timestep_reduction`` times its default value. "
"Accuracy can be improved with a smaller time step size, but the simulation time will be increased.",
lt=1,
ge=0,
)
LossyMetalSubpixelType = discriminated_union(
Union[Staircasing, VolumetricAveraging, SurfaceImpedance]
)
[docs]
class SubpixelSpec(Tidy3dBaseModel):
"""Defines specification for subpixel averaging schemes when added to ``Simulation.subpixel``."""
dielectric: DielectricSubpixelType = Field(
default_factory=PolarizedAveraging,
title="Subpixel Averaging Method For Dielectric Interfaces",
description="Subpixel averaging method applied to dielectric material interfaces.",
)
metal: MetalSubpixelType = Field(
default_factory=Staircasing,
title="Subpixel Averaging Method For Metallic Interfaces",
description="Subpixel averaging method applied to metallic structure interfaces. "
"A material is considered as metallic if its real part of relative permittivity "
"is less than 1 at the central frequency.",
)
pec: PECSubpixelType = Field(
default_factory=PECConformal,
title="Subpixel Averaging Method For PEC Interfaces",
description="Subpixel averaging method applied to PEC structure interfaces.",
)
pmc: PMCSubpixelType = Field(
default_factory=Staircasing,
title="Subpixel Averaging Method For PMC Interfaces",
description="Subpixel averaging method applied to PMC structure interfaces.",
)
lossy_metal: LossyMetalSubpixelType = Field(
default_factory=SurfaceImpedance,
title="Subpixel Averaging Method for Lossy Metal Interfaces",
description="Subpixel averaging method applied to ``td.LossyMetalMedium`` material interfaces.",
)
[docs]
@classmethod
def staircasing(cls) -> Self:
"""Apply staircasing on all material boundaries."""
return cls(
dielectric=Staircasing(),
metal=Staircasing(),
pec=Staircasing(),
pmc=Staircasing(),
lossy_metal=Staircasing(),
)
[docs]
def courant_ratio(self, contain_pec_structures: bool, contain_sibc_structures: bool) -> float:
"""The scaling ratio applied to Courant number so that the courant number
in the simulation is ``sim.courant * courant_ratio``. So far only PEC subpixel averaging
scheme and SIBC require deduction of Courant number.
"""
if contain_pec_structures and contain_sibc_structures:
return min(self.pec.courant_ratio, self.lossy_metal.courant_ratio)
if contain_pec_structures:
return self.pec.courant_ratio
if contain_sibc_structures:
return self.lossy_metal.courant_ratio
return 1.0
