# Geometry and Materials

Channel: release; package: 1.8.0; source: 7d1e97331656dd74ad0f5471653ac0c5effdff70

Page: https://remilab.ai/rfx/versions/v1.8.0/api/geometry-materials/
Source: https://github.com/bk-squared/rfx/blob/7d1e97331656dd74ad0f5471653ac0c5effdff70/docs/public/api/geometry-materials.mdx

Geometry should stay explicit in public examples.
The documented API includes the shapes and named materials below. An available
constructor alone does not establish RF accuracy; pair it with a configuration
listed in [Recommended Configuration](https://remilab.ai/rfx/versions/v1.8.0/validation/reference-lane/) and
[Support Boundaries](https://remilab.ai/rfx/versions/v1.8.0/api/support-boundaries/).

## Shapes

| Shape | Signature | Typical use |
|---|---|---|
| `Box` | `Box(corner_lo, corner_hi)` | substrates, ground planes, patch metal, dielectric blocks |
| `Sphere` | `Sphere(center, radius)` | resonators, scatterers, simple inclusions |
| `Cylinder` | `Cylinder(center, radius, height, axis="z")` | vias, posts, cylindrical inclusions |
| `PolylineWire` | polyline-defined wire geometry | wire-like studies and routed conductors |
| `Via` | `Via(center=..., drill_radius=..., pad_radius=..., layers=..., material="pec")` | PCB-style interconnects |
| `CurvedPatch` | `CurvedPatch(center=..., length=..., width=..., radius=..., axis="x")` | curved-conductor studies; constructor arguments are keyword-only |
| `MeshShape` | `MeshShape.from_file(path, scale=..., translate=(0,0,0))` | CAD import — STL/OBJ/PLY, plus STEP/STP via the `cad` extra. Rasterizes host-side (trimesh containment): NOT differentiable — a traced coordinate raises, so CAD geometry cannot carry gradients |

## Material registration

Setup used by the snippets below:

```python
from rfx import Simulation

sim = Simulation(
    freq_max=5e9,
    domain=(0.04, 0.03, 0.02),
    dx=2e-3,
    boundary="cpml",
    cpml_layers=6,
)
```

```python
from rfx import DebyePole, LorentzPole

sim.add_material("fr4", eps_r=4.3, sigma=0.02)
sim.add_material("resistive_medium", sigma=5.0e5)
sim.add_material(
    "custom_dielectric",
    eps_r=6.0,
    debye_poles=[DebyePole(delta_eps=12.0, tau=9.4e-12)],
)
```

### Material arguments

| Argument | Meaning | Notes |
|---|---|---|
| `eps_r` | relative permittivity | default is 1.0 |
| `sigma` | conductivity | lossy dielectrics and below-threshold conductors; `sigma >= 1e6` S/m is represented by the PEC mask |
| `mu_r` | relative permeability | default is 1.0 |
| `debye_poles` | dispersive Debye terms | `DebyePole(delta_eps, tau)` |
| `lorentz_poles` | dispersive Lorentz terms | `LorentzPole(omega_0, delta, kappa)` |
| `chi3` | third-order nonlinearity | specialized nonlinear-material workflows |

Materials such as the built-in `"copper"` and `"aluminum"` have conductivity
above the `1e6` S/m threshold and therefore behave as PEC in the compiled grid;
their bulk skin depth and ohmic loss are not resolved. Use
`add_thin_conductor(...)` when a subcell sheet model is appropriate. That helper
also maps `sigma_bulk >= 1e6` S/m (including its default copper value) to PEC;
a finite sheet resistance requires an explicitly justified
`sigma_bulk < 1e6` S/m. Use a below-threshold volumetric conductivity only when
its cells and loss model match the intended physical approximation.

## Configuration limits

Geometry and materials are covered only when paired with a documented boundary,
source or port, mesh, and observable combination. Check
[Support Boundaries](https://remilab.ai/rfx/versions/v1.8.0/api/support-boundaries/) before reporting RF accuracy for a
structure that uses a limited configuration.

Two current opt-in conductor realizations have narrower contracts:

- `add(shape, material="pec", two_plane=True)` is hard-PEC-only and
  face-registers a one-cell PEC body on both node planes. A non-PEC material
  raises `ValueError`. It is supported only on the uniform `run()`/`forward()`
  scan and the single-device non-uniform runner.
- `add_thin_conductor(shape, surface_impedance_f0=...)` applies a band-centre
  Leontovich sheet resistance to any rasterizable patterned shape that occupies
  exactly one cell layer and at least one cell. Unsupported solver, boundary,
  overlap, and port-family combinations fail explicitly.