ems

A pure Rust FDTD (finite-difference time-domain) electromagnetic field solver, intended as a replacement for openEMS.

• Clean-room implementation: no openEMS or CSXCAD code was consulted. See CLEANROOM.md. MIT licensed.
• Models come from csx, the companion CSXCAD-compatible geometry and material crate. ems adds the solver: mesh compilation, time stepping, boundaries, sources, probes, ports, and post-processing.
• Goal: run existing openEMS XML models unchanged.
• Edition 2024, MSRV 1.95.

Status: early development (milestones 1, 3 and 4 done, milestone 2 done except the openEMS output-file layout). The API will still change. See docs/DESIGN.md for the architecture and roadmap.

Quick start

Build a model with csx, describe the solver settings with ems::Fdtd, run it, and analyse the port:

use csx::primitives::BoxShape;
use csx::{ContinuousStructure, Primitive, Property};
use ems::prelude::*;

let mut model = ContinuousStructure::new();
model.grid.delta_unit = 1e-3; // drawing unit: mm
model.grid.set_lines(0, (0..=40).map(f64::from))?;
model.grid.set_lines(1, (0..=40).map(f64::from))?;
model.grid.set_lines(2, (0..=20).map(f64::from))?;
// 2 mm FR-4 on a ground plane (the PEC z_min face), a 12 mm square patch
// on top; everything stays clear of the 8-cell PML on the other faces.
let sub = model.add_property(Property::material("sub", csx::Material::new(4.3, 0.0)));
model.add_primitive(
    sub,
    Primitive::new(BoxShape::new([10., 10., 0.], [30., 30., 2.])),
)?;
let patch = model.add_property(Property::metal("patch"));
model.add_primitive(
    patch,
    Primitive::new(BoxShape::new([14., 14., 2.], [26., 26., 2.])),
)?;
let port = LumpedPort::new(1, 50.0, [17., 20., 0.], [17., 20., 2.], Axis::Z)
    .excite(1.0)
    .add_to(&mut model)?; // writes LumpedElement + Excitation + probes into the model

let fdtd = Fdtd::new()
    .waveform(Waveform::gaussian(2e9, 1e9))
    .boundaries(Boundaries::all(Boundary::pml(8)).with(Face::ZMin, Boundary::Pec))
    .end_criteria(EndCriteria::energy_decay_db(-40.0));
let mut sim = Simulation::new(&model, &fdtd)?;
for w in sim.warnings() {
    eprintln!("warning: {w}"); // includes the solver-aware mesh checks
}
let res = sim.run()?;
let z_in = port.analyze(&res, &[1e9, 2e9, 3e9])?.z_in();

Run an existing openEMS XML file (Simulation::from_xml in the API):

cargo run --release --example run_xml -- model.xml [--threads N] [--out DIR]

It prints warnings, progress and the outcome, and writes every probe as DIR/<name>.csv and every dump as .vtr files. More examples: cavity, microstrip, waveguide, patch_antenna, dipole (cargo run --release --example <name>).

Status

Features

Documentation

License

MIT. See LICENSE.