# Watch a pulse meet a dielectric

Channel: development; package: 2.0.0rc1; source: 2c32b7cf79b796fae825bfa08fc73d9914e61723

Page: https://remilab.ai/rfx/gallery/dielectric-interface/
Source: https://github.com/bk-squared/rfx/blob/2c32b7cf79b796fae825bfa08fc73d9914e61723/docs/public/gallery/dielectric-interface.mdx

**Current-run teaching example · actual FDTD snapshots · 2D TMz · single mesh**

Place a dielectric on the right side of the same open domain. The pulse reaches
the interface, produces a reflected part, and propagates differently inside
the material. The vacuum reference on the left makes the changed field and
probe arrival easier to see.

![Video poster](https://remilab.ai/rfx/gallery/assets/current-visuals/dielectric-interface.png)

  [source](https://remilab.ai/rfx/gallery/assets/current-visuals/dielectric-interface.mp4)

  [Download the interface movie](https://remilab.ai/rfx/gallery/assets/current-visuals/dielectric-interface.mp4)

**Teaching mesh:** preflight reports resolution advisories for the dielectric
at the declared band edge. This movie is qualitative; it does not establish
phase-velocity accuracy or reflection/transmission coefficients.

## The model

| Model detail | Value |
|---|---|
| Cross-section | 80 × 60 mm; uniform Yee 2D TMz with 1 mm cells |
| Left panel | Vacuum reference |
| Right panel | Vacuum for `x < 40 mm`, ideal nondispersive dielectric `εr = 4` for `x ≥ 40 mm` |
| Boundary | 16 CPML layers outside the physical domain |
| Source | Same differentiated Gaussian current pulse in both models at (20, 30) mm |
| Probe | `Ez` at (55, 30) mm |
| Recording | 640 steps, actual field snapshot every 4 steps |

The dielectric extends through the right absorber and the transverse edges;
there is no second material interface in the simulated interior. The dashed
line is the declared interface on the 40 mm grid plane. The source is a point
in this 2D model, so the wavefront is curved; this is not a normally incident
infinite plane wave.

Both panels use the same fixed signed `Ez / Eref` scale. `Eref` is the largest
absolute recorded field outside a 4 mm source neighborhood across both models.
The source pixels can saturate, and all unmodified values remain in the data.
The green-probe trace and cursor share the movie's actual simulation time.

## Run and explore

Follow the pinned installation and generator download in
[the boundary example](https://remilab.ai/rfx/gallery/boundary-reflection/#run-this-example), then:

```bash
JAX_PLATFORMS=cpu PYTHONPATH=. python field_movies.py \
  --case dielectric-interface --output field-movies
```

Try a different permittivity or move the interface. Rerun preflight and the
simulation; a higher permittivity shortens the material wavelength and may
require a finer mesh. For a quantitative slab spectrum, continue with the
[slab reflection/transmission tutorial](https://github.com/bk-squared/rfx/blob/a9054338616b91bb1364699882c2530fa29a0048/examples/tutorials/slab_rt_flux_monitor.py),
which uses flux monitors and reference subtraction.

## Preflight is part of the result

The manifest preserves the complete preflight output. Five advisories were
reported and retained:

- Three resolution findings: the dielectric has 12.5 cells per effective
  wavelength at the declared 12 GHz band edge, below the 15-cell recommendation.
- Geometry reaches into CPML because this example models a continuing
  half-space. Absorber-region fields are excluded from the plotted interior.
- The material is perfectly lossless in an open domain. This example does not
  extract Q, material loss or an absorption fraction.

No advisory was suppressed to make a clean banner. No mesh refinement or
record-length convergence claim is made.

## Download the actual samples

- [Probe traces, CSV in seconds and V/m](https://remilab.ai/rfx/gallery/assets/current-visuals/dielectric-interface.csv)
- [Selected field arrays and all probe samples, NPZ](https://remilab.ai/rfx/gallery/assets/current-visuals/dielectric-interface.npz)
- [Model, preflight output, normalization and checksums, JSON](https://remilab.ai/rfx/gallery/assets/current-visuals/dielectric-interface.json)
- [Complete generator](https://remilab.ai/rfx/gallery/assets/current-visuals/field_movies.py)

The NPZ contains every 16th movie frame at full spatial resolution. Its
`*_frame_times_s`, `*_frame_steps`, `*_x_m` and `*_y_m` arrays describe the exact
samples. Local regeneration retains every frame. Fields were checked for
finite values; displayed coordinates and time steps were checked against
`Result.snapshot_axes`. The solver source is `a9054338`; the manifest records
the full SHA, generator hash and CPU environment.