The Electric Currents (ec) interface (), under the AC/DC>Electric Fields and Currents branch when adding a physics interface, is used to compute electric field, current, and potential distributions in conducting media under conditions where inductive effects are negligible; that is, when the skin depth is much larger than the studied device.

Current Conservation is the main node, which adds the equation for the electric potential and provides a Settings window for defining the electrical conductivity as well as the constitutive relation for the electric displacement field and its associated material properties, such as the relative permittivity.

When this physics interface is added, these default nodes are also added to the Model Builder — Current Conservation, Electric Insulation (the default boundary condition), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and current sources. You can also right-click Electric 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 ec.

Enter a default value for the Cross-section area A (SI unit: m2). The default value of 1 m2 is typically not representative for a small domain. Instead it describes a unit area that makes the 1D equation identical to the equation used for 3D components. See also Change Cross Section (described for the Electrostatics interface).

Enter a default value for the Out-of-plane thickness d (SI unit: m) (see Equation 2-17). The default value of 1 m is typically not representative for a thin dielectric medium, for example. Instead it describes a unit thickness that makes the 2D equation identical to the equation used for 3D components. See also Change Thickness (Out-of-Plane) (described for the Electrostatics interface).

Enter a Reference impedance Zref (SI unit: Ω). The default is 50 Ω.

Select the Use manual terminal sweep check box to switch on the sweep and invoke a parametric sweep over the terminals. Enter a Sweep parameter name to assign a specific name to the variable that controls the terminal number solved for during the sweep. The default is PortName. The generated lumped parameters are in the form of capacitance matrix elements. The terminal settings must consistently be of either fixed voltage or fixed charge type.

The lumped parameters are subject to Touchstone file export. 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.

The dependent variable is the Electric potential V. You can change its name, which changes both the field name and the variable name. If the new name coincides with the name of another electric potential field in the model, the physics interfaces share degrees of freedom. The new name must not coincide with the name of a field of another type or with a component name belonging to some other field.

Select the shape order for the Electric potential dependent variable — Linear, Quadratic (the default), Cubic, Quartic, or Quintic. For more information about the Discretization section, see Settings for the Discretization Sections in the COMSOL Multiphysics Reference Manual.