The Electrostatics Interface
The Electrostatics (es) interface (), found under the AC/DC branch () when adding a physics interface, is used to compute the electric field, electric displacement field, and potential distributions in dielectrics under conditions where the electric charge distribution is explicitly prescribed. The formulation is stationary except for use together with other physics interfaces. Eigenfrequency, frequency-domain, small-signal analysis, and time-domain modeling are supported in all space dimensions.
The physics interface solves Gauss’ Law for the electric field using the scalar electric potential as the dependent variable.
Charge Conservation is the main node, which adds the equation for the electric potential and has a Settings window for defining the constitutive relation for the electric displacement field and its associated properties such as the relative permittivity.
When this physics interface is added, these default nodes are also added to the Model BuilderCharge Conservation, Zero Charge (the default boundary condition), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and space charges. You can also right-click Electrostatics to select physics features from the context menu.
Settings
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 es.
Cross-Section Area (1D components)
For 1D components, enter a default value for the Cross-section area A (SI unit: m2). The default value of 1 is typically not representative for a thin domain. Instead it describes a unit thickness that makes the 1D equation identical to the equation used for 3D components. See also Change Cross Section.
Thickness (2D components)
For 2D components, enter a default value for the Out-of-plane thickness d (SI unit: m). The default value of 1 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).
Physics-Controlled Mesh
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 set up automatically an appropriate mesh sequence.
Manual Terminal Sweep Settings
Enter a Reference impedance Zref (SI unit: Ω). The default is 50 Ω.
Select the Activate 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 Sweep parameter name must also be declared as a model parameter. 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.
From the Home toolbar add a Parameters node and enter the chosen name and assign to it a temporary Expression of unity into the Parameters table. You can also right-click Global Definitions to add the node.
For most applications it is simpler to sweep over terminals using the Stationary Source Sweep study step. See Stationary Source Sweep in the COMSOL Multiphysics Reference Manual and (for more details) Stationary Source Sweep in the AC/DC Module User’s Guide.
Dependent Variables
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 shares 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.
Discretization
In the COMSOL Multiphysics Reference Manual, see Table 2-3 for links to common sections and Table 2-4 to common feature nodes. You can also search for information: press F1 to open the Help window or Ctrl+F1 to open the Documentation window.
Electric Sensor: Application Library path COMSOL_Multiphysics/Electromagnetics/electric_sensor