The Magnetic and Electric Fields (mef) interface (), found under the AC/DC>Electromagnetic Fields>Vector Formulations branch when adding a physics interface, is used to compute magnetic field and current distributions when the exciting current is driven by an applied voltage. Stationary, time-dependent, and frequency-domain modeling are supported in 2D and 3D. Note that in most cases, using the Magnetic Fields interface with its dedicated coil modeling features is the preferred choice over using the Magnetic and Electric Fields interface.

The main node is the Ampère’s Law and Current Conservation feature, which adds the equation for the electric potential and magnetic vector potential and provides an interface for defining the constitutive relations and their associated properties such as the relative permeability, relative permittivity, and electrical conductivity.

The Ampère’s Law and Current Conservation feature can be overridden with an Ampère’s Law feature or a Coil feature, that are identical to the ones in the Magnetic Fields interface, removing the electric potential and the current conservation equation from the selected domains.

When this physics interface is added, these default nodes are also added to the Model Builder — Ampère’s Law and Current Conservation, Magnetic Insulation (the default boundary condition for the magnetic vector potential), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and external currents. You can also right-click Magnetic and Electric 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.

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 mef.

The only option available from the Solve for list is Full field.

Enter a Reference impedance Zref (SI unit: Ω). The default is 50 Ω. This impedance is used by Terminal features (when the Terminal Type is set to Terminated) and the Touchstone file export functionality.

Select the Activate input sweep check box to switch on the sweep and invoke a parametric sweep over the Lumped ports or the Terminal nodes.

Select an option from the Sweep on list — Terminals or Ports. This setting controls which features are activated during the sweep.

Enter a Sweep parameter name to indicate the name of the model parameter that controls the terminal or 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 the 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 Browse for 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 an option from the If file exists list — Overwrite or Create new. Create new is useful when the model is solved multiple times with different settings. Select a Parameter to export — Z (the default), Y, or S.

When Terminals is selected under Sweep on, also select a Parameter to export — Z (the default), Y, or S. When the sweep is carried on Ports, the exported parameter is always S.

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 variables (field variables) are for the Electric potential V and 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), or Cubic and for the Electric 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.