The Magnetic Fields, Currents Only (mfco) interface (), found under the AC/DC>Magnetic Fields>Vector Formulations branch when adding a physics interface, is used to compute magnetic fields from currents under the assumption that all regions have a uniform relative magnetic permeability of one. It is designed to support both divergence-free and non-divergence-free currents. In free space it returns the value of the Biot–Savart integral. The interface supports the Stationary, Stationary Source Sweep, and Frequency Domain Source Sweep study steps in 3D.

The physics interface solves Ampère’s law using the magnetic vector potential as the dependent variable. The main node is the Free Space feature which solves Ampère’s law in free space. It is designed to efficiently compute the lumped inductance matrix of complex circuits. Due to the support of modeling non-divergence-free currents, this interface is able to calculate the partial contributions of magnetic fields generated from open conductors.

When this physics interface is added, these default nodes are also added to the Model Builder — Magnetic Fields, Currents Only, Free Space, Exterior Boundaries (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, Currents Only 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 mfco.

The dependent variable (field variable) is for the Magnetic vector potential A. 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 vector potential dependent variable — Linear, Quadratic (the default), Cubic, or Quartic. For more information about the Discretization section, see Settings for the Discretization Sections in the COMSOL Multiphysics Reference Manual.