The Magnetic Fields, No Currents (mfnc) interface (), found under the AC/DC>Magnetic Fields, No Currents branch when adding a physics interface, is used to compute magnetostatic fields from permanent magnets and other current free magnetic sources. The formulation is stationary but for use together with other physics also time-domain modeling is supported in 2D and 3D.

The main node is the Magnetic Flux Conservation feature, which adds the equation for the magnetic potential and provides an interface for defining the material properties and the constitutive relation for the magnetic flux density. It is used when there are no currents and all the magnetic fields are originated by permanent magnets or external systems not included in the model.

When this physics interface is added, these default nodes are also added to the Model Builder — Magnetic Fields, No Currents, Magnetic Flux Conservation, Magnetic Insulation (the default boundary condition), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, additional boundary conditions and point conditions. You can also right-click Magnetic Fields, No Currents 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.

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 mfnc.

Select an option from the Solve for list — Reduced field or Full field (the default). For Reduced field specify a Background magnetic field Hb (SI unit: A/m). The entered expressions must be differentiable.

To display this section, click the Show More Options 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.

The dependent variable (field variable) is for the Magnetic scalar potential Vm. The name can be changed but the names of fields and dependent variables must be unique within a model.

Select the shape order for the Magnetic scalar 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.