The Magnetic Fields (mf) interface (
), found under the
AC/DC>Electromagnetic Fields branch when adding a physics interface, is used to compute magnetic field and induced current distributions in and around coils, conductors, and magnets. Depending on the licensed products, stationary, frequency-domain, small-signal analysis, and time-domain modeling are supported in 2D and 3D. Note that the frequency and time-domain formulations become ill-posed when approaching the static limit. You can extend the useful frequency range downward by adding a low conductivity.
When this physics interface is added, these default nodes are also added to the Model Builder —
Magnetic Fields,
Ampère’s Law,
Magnetic Insulation (the default boundary condition), and
Initial Values. Then, from the
Physics toolbar, add other nodes that implement boundary conditions and external currents. You can also right-click
Magnetic Fields to select physics features from the context menu.
The physics-controlled mesh is controlled from the Mesh node’s
Settings window (if the
Sequence type is
Physics-controlled mesh). There, in the table in the
Physics-Controlled Mesh section, find the physics interface in the
Contributor column and select or clear the check box in the
Use column on the same table row for enabling (the default) or disabling contributions from the physics interface to the physics-controlled mesh.
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In the COMSOL Multiphysics Reference Manual see the Physics-Controlled Mesh section for more information about how to define the physics-controlled mesh.
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The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern
<name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the
name string must be unique. Only letters, numbers, and underscores (_) are permitted in the
Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is
mf.
Select an option to Solve for —
Full field (the default) or
Reduced field. When
Reduced field is selected, choose the Background field specification —
Magnetic vector potential (the default) or
Uniform magnetic flux density. Mathematically, the background field is always specified as a background magnetic vector potential. The
Uniform magnetic flux density option will apply an appropriate magnetic vector potential generating the specified magnetic flux density. In axisymmetric geometries, the uniform background field is applied in the axial direction.
For Magnetic vector potential, enter values or expressions for the
Background magnetic vector potential Ab (SI unit: Wb/m). The defaults are 0 Wb/m. For
Uniform magnetic flux density, in 2D or 3D components, enter the values or expressions of the components of the
Uniform magnetic flux density Bb (SI unit: T); in 2D axisymmetric components, enter the value or expression of the
Uniform axial magnetic flux density Bb,z (SI unit: T). The defaults are 0 T. The specified background magnetic flux densities must be uniform (space-independent), but they can be a function of time.
Select Components —
Out-of-plane vector potential (the default),
In-plane vector potential, or
Three-component vector potential for the magnetic vector potential.
When In-plane vector potential or
Three-component vector potential is selected, the
Gauge Fixing for A-Field node becomes available.
For 2D components, enter a value or expression for the global Out-of-plane thickness d (SI unit: m). The default of 1 m is typically not representative for a thin domain. Instead it describes a unit thickness that makes the 2D equation identical to the equation used for 3D components.
Use the Change Thickness (Out-of-Plane) node (described for the Electrostatics interface) to define specific geometric entities (for example, domains) instead of a global setting for the thickness.
Select the Activate port sweep check box to switch on the sweep and invoke a parametric sweep over the Lumped Port features. Enter a
Sweep parameter name to indicate the name of the model parameter that controls the port activated in each step of the sweep. The default is
PortName. The name given must match the model parameter, defined under
Global Definitions, that is object of a
Parametric Sweep node in the current
Study.
The lumped parameters computed can be subject to a Touchstone file export. To activate this functionality, enter a file path or click
Browse to navigate to a file. Select a
Parameter format (value pairs) for the Touchstone export —
Magnitude and angle (MA) (the default),
Magnitude in dB and angle (DB), or
Real and imaginary parts (RI). Select the desired operation to perform from the
If file exists list —
Overwrite (the default) or
Create new. The latter is useful when the model is solved multiple times with different settings. Enter a
Reference impedance, Touchstone file export Zref (SI unit:
Ω). The default is 50
Ω.
To display this section, click the Show More Options button (
) and select
Advanced Physics Options in the
Show More Options dialog box.
When the Check applicability of features in study check box is selected, any features that are incompatible with the study will generate an error message when trying to solve or show the default solver. No solver will be generated. Clear the check box and you will be able to run the model, possibly with runtime errors instead. It is available to allow the advanced user to tweak any feature and use it outside of its intended study scope.
The dependent variable is the Magnetic vector potential A. You can change both its field name and the individual component variable names. If the new field name coincides with the name of another magnetic vector potential field in the model, the physics interfaces share degrees of freedom and component names. The new field name must not coincide with the name of a field of another type, or with a component name belonging to some other field. Component names must be unique within a model, except for fields of the same type sharing a common field name.
Select the shape order for the Magnetic vector potential dependent variable —
Linear,
Quadratic (the default), or
Cubic. For more information about the
Discretization section, see
Settings for the Discretization Sections in the
COMSOL Multiphysics Reference Manual.
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Quadrupole Lens: Application Library path COMSOL_Multiphysics/Electromagnetics/quadrupole
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Eddy Currents: Application Library path ACDC_Module/Introductory_Electromagnetics/eddy_currents
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