The Magnetic Fields (mf) interface (), found under the AC/DC 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. One may 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 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.

When a background field is active, this solves for the relative (perturbated) field only. This setting, together with the External Magnetic Vector Potential feature, is useful to introduce an external field generated by systems not included in the model.

The current vector has the same direction as the magnetic vector potential. This setting also controls the direction in which applied and induced currents can flow in the model. The default option is to solve for the out-of-plane component only for 2D and 2D axisymmetric 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 button () and select Advanced Physics Options.

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. Deselect it 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.

Select the Enable check box to allow the physics interface to control the meshing process. Information from the physics, such as the presence of an infinite elements domain or periodic condition, will be used to automatically set up an appropriate mesh sequence.

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.