openEMS is a free, open-source FDTD (Finite-Difference Time-Domain) electromagnetic field solver. It is the core simulation engine of the openEMS-Project and is used together with CSXCAD for geometry and material description.

• License: GPLv3
• Website: https://openEMS.de
• Docs: https://docs.openems.de
• Discussions: https://github.com/thliebig/openEMS-Project/discussions

• 3-D FDTD solver for electromagnetic wave propagation
• Cartesian and cylindrical (including multi-grid) coordinate systems
• SIMD-accelerated engines (SSE2, multi-threaded, optional MPI)
• Uniaxial PML and Mur ABC absorbing boundary conditions
• Total-field / scattered-field (TFSF) excitation
• Lumped RLC elements
• Dispersive materials: Drude, Lorentz, Debye (full multi-polar)
• Near-field to far-field (NF2FF) transformation (standalone tool + library)
• SAR calculations (1g / 10g averaging)
• HDF5 and VTK field dump output
• Scripting via Octave / Matlab and Python (Cython bindings)

openEMS/
├── openems.h / openems.cpp   # Top-level openEMS class (orchestrator)
├── main.cpp                  # openEMS binary entry point
├── FDTD/                     # Operator + Engine (Yee-mesh EC coefficients, time-stepping)
│   └── extensions/           # Physics add-ons (PML, excitation, lumped elements, …)
├── Common/                   # Processing classes (field dumps, ports, NF2FF, SAR)
├── tools/                    # Utility helpers (array types, constants, …)
├── nf2ff/                    # Near-field to far-field tool (libnf2ff + nf2ff binary)
├── matlab/                   # Octave/Matlab scripting interface
└── python/openEMS/           # Cython bindings + pure-Python helpers (ports, automesh, …)

openEMS is normally built as part of the openEMS-Project meta-repo using the update_openEMS.sh script, which handles all dependencies automatically. See the openEMS-Project README for the recommended full-stack build.

Required dependencies: CSXCAD, fparser, TinyXML, HDF5, VTK, Boost (≥ 1.46, components: thread, date_time, serialization, chrono, program_options).

mkdir build && cd build
cmake .. \
  -DCMAKE_INSTALL_PREFIX=~/opt/openEMS \
  -DFPARSER_ROOT_DIR=~/opt/openEMS \
  -DCSXCAD_ROOT_DIR=~/opt/openEMS
make -j$(nproc)
make install

Developer-local path overrides go in localConfig.cmake (gitignored) at the repo root — this avoids having to pass -D flags every time:

# localConfig.cmake
SET(CMAKE_INSTALL_PREFIX  "$ENV{HOME}/opt/openEMS")
SET(FPARSER_ROOT_DIR      "$ENV{HOME}/opt/openEMS")
SET(CSXCAD_ROOT_DIR       "$ENV{HOME}/opt/openEMS")

The build produces libopenEMS.so and the openEMS binary, both installed under <prefix>/lib and <prefix>/bin.

After make install, run the Octave setup once to compile the HDF5 helper:

octave --no-gui --eval "setup()"

The CSXCAD Python module must be installed first (from the CSXCAD repo):

python3 -m venv ~/.venv/openEMS
source ~/.venv/openEMS/bin/activate

# 1. Install CSXCAD Python module
export CSXCAD_INSTALL_PATH=~/opt/openEMS
cd /path/to/CSXCAD/python && pip install .

# 2. Install openEMS Python module
export OPENEMS_INSTALL_PATH=~/opt/openEMS
cd /path/to/openEMS/python && pip install .

Verify from outside the source tree:

python3 -c "import CSXCAD; print(CSXCAD.__version__)"
python3 -c "import openEMS; print(openEMS.__version__)"

After installation, follow the official tutorials to run your first simulation:

• Octave/Matlab tutorials: https://docs.openems.de — also available locally in matlab/Tutorials/
• Python tutorials: https://docs.openems.de/python/openEMS/Tutorials/ — also available locally in python/Tutorials/

Octave smoke-test (fastest sanity check):

cd .github/smoketests/octave
octave MSL_NotchFilter.m

Python smoke-test:

cd .github/smoketests/python
python3 MSL_NotchFilter.py

Full Octave test suite:

cd TESTSUITE
octave --no-gui run_testsuite.m

Python unit tests:

python3 -m unittest discover -s python/Tests -p "test_*.py" -v

Pull requests are welcome. Please:

1. Follow the existing code style (C++11, no trailing whitespace — enforced by CI).
2. Add or update tests in TESTSUITE/ for non-trivial changes.
3. Disclose AI tool usage per AI_POLICY.md.
4. Include Signed-off-by: Your Name <email> in commit messages (DCO).

openEMS is free software licensed under the GNU General Public License v3. See COPYING for the full text.

Copyright © 2010-2026 Thorsten Liebig and contributors.