Excitation Coil Model¶

Introduction¶

Excitation coils are widely used in electromagnetic devices such as motors, transformers, and inductors. They generate magnetic fields by driving electric current through conductors.

Examples of excitation coils used in electromagnetic applications

A transformer with a primary and secondary coil. Both coils consist of thin wires wound many times around a magnetic core. (image credit: CC BY-SA 4.0).

This model allows the definition of different coil geometries, topologies, and excitation types using a unified and physically consistent framework.

To add an excitation coil model to a simulation:

from mufem.electromagnetics.coil import ExcitationCoilModel

coil_model = ExcitationCoilModel()
sim.get_model_manager().add_model(coil_model)

Coil Specification¶

Each coil is described using a CoilSpecification, which defines:

• Name — identifier of the coil
• Marker — the geometric region or boundary to which the coil applies
• Coil type — physical realization of the winding
• Coil topology — whether terminals are open or closed
• Coil excitation — how the coil is electrically driven

All of these are required.

from mufem.electromagnetics.coil import CoilSpecification

coil = CoilSpecification(
    name="Coil",
    marker=my_coil_marker,
    topology=my_coil_topology,
    type=my_coil_type,
    excitation=my_coil_excitation
)

coil_model.add_coil_specification(coil)

Coil Topology¶

The coil topology specifies how the electrical circuit connects to the coil.

Name	Description	Illustration
Open coil	The coil has electrical terminals. Current enters and leaves through designated boundary faces.
Closed coil	The coil is electrically closed. Current circulates internally without terminals.

Coil Type¶

The coil type defines how the conductor is physically represented.

Name	Description	Illustration
Stranded coil	Individual wires are not resolved. The winding is modeled as a homogenized conducting region. Valid when strand diameter is much smaller than the skin depth. Common in motors, transformers, and actuators.
Solid coil	The entire conductor is explicitly meshed. Eddy currents are fully resolved. Required when skin depth is comparable to conductor size.
Litz wire coil	Consist of individual strands which are twisted and insulating between each other in order to reduce eddy current losses. Used at high frequencies to suppress skin and proximity effects.
Foil coil	The coil consists of layered conducting foils separated by insulation. Current flows within each foil but not between layers. Common in high-current transformer windings.

Coil Excitation¶

A coil is driven by an electrical source. It possesses intrinsic resistance and inductance, which produce ohmic losses and magnetic energy storage.

Name	Description	Illustration
Current excitation	The coil current is prescribed directly.
Voltage excitation	A voltage is applied. Coil resistance and inductance determine the resulting current.

Reports¶

Available reports. Note that some are only available with the Time-Domain Magnetic Model.

Example¶