Terminal
The Terminal node provides a boundary or domain condition for connection to external circuits, to transmission lines, or with a specified voltage or charge. By specifying zero charge, a floating potential condition is obtained.
In most cases, it is not recommended to include the interior of good conductors in the simulation. When using the Terminal on the domain level, the interior unknowns for the electric potential are automatically replaced by a single constant, thus avoiding numerical problems arising from a very high material contrast. If one instead uses the Terminal on the boundary level, it is recommended to exclude the interior of the associated conductor from the domain selection for the main Electrostatics node.
An operation called Split by Connectivity () is available by right-clicking the parent node. The operation is useful when there are several terminal domains or boundaries that are not geometrically connected. Clicking the operation node will automatically generate several Terminal nodes where each selection is geometrically connected.
The Terminal node also enables the computation of the lumped parameters of the system, such as capacitance. See Computing Lumped Parameters.
Terminal
Specify the terminal properties. Enter a unique Terminal name that will be used to identify the global variables (such as the terminal voltage or current) that are defined by the terminal. The Terminal name can contain alphanumeric characters, but it should be numeric when performing terminal sweeps.
Select a Terminal type — Charge (the default), Voltage, Circuit, Terminated (power), or Terminated (voltage). Select:
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Charge to prescribe the total charge deposited on the terminal boundaries. Enter the total charge Q0. The default is 0 C, which corresponds to a uncharged floating electrode.
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Voltage to specify a fixed electric potential at the terminal. Enter an electric potential V0. The default is 1 V.
To correctly calculate the terminal charge and the corresponding capacitances, if Voltage Terminal is used on boundaries between The Electrostatics Interface and The Electrostatics, Boundary Elements Interface, let the dependent variable for The Electrostatics, Boundary Elements Interface be the same as the dependent variable for The Electrostatics Interface and disable Electric Scalar–Scalar Potential Coupling. How to set the name for the dependent variable is described in the Dependent Variables section. Since the Electric Scalar–Scalar Potential Coupling is disabled, add manually a Fully Coupled node to the Stationary Solver below the Solution node in the Solver Configurations.
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Circuit to specify a terminal connected to an Electrical Circuit interface that models an external circuit. The Terminal node provides a current-voltage characteristic to the circuit.
The Electrical Circuit Interface requires a current from the Terminal, so the Circuit terminal type can only be used in Time Dependent or Frequency Domain studies, in which the current can be computed as the time derivative of the charge.
The Circuit type cannot be used together with a terminal sweep.
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Terminated (power) to connect the terminal to an impedance that might represent a load or a transmission line. When Terminated (power) is selected, the scattering parameters (S-parameters) are computed. The Terminated (power) setting can only be used in frequency-domain studies.
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Enter a Terminal power P0 to specify the input power at this terminal from the transmission line. This excitation can be toggled using a port sweep.
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Select an option from the Characteristic impedance from list to define the value of the impedance — Physics interface or User defined. For Physics interface, the Reference impedance Zref defined in the Settings window for the physics under Sweep Settings is used. For User defined, enter a specific impedance Zref for this terminal. The default is 50 Ω.
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Terminated (voltage) to connect the terminal to an impedance that might represent a load or a transmission line. The Terminated (voltage) option is essentially the same as Terminated (power), with the power defined as: .
When Terminal type is selected as Charge or Voltage, a contribution can be added as Harmonic Perturbation by right-clicking the parent node or clicking Harmonic Perturbation in the Physics toolbar. For more information see Harmonic Perturbation — Exclusive and Contributing Nodes in the COMSOL Multiphysics Reference Manual.
Advanced Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.
The Advanced Settings subsection is used to provide symmetry options for the Terminal, and to provide initial values for its internal state variables.
The Terminal area multiplication factor can be used to include the effects of symmetry. If a mirror symmetry has been used in the model such that the surface area of the Terminal boundary selection is half of the surface area of the full device, use a multiplication factor of two. Higher numbers can be used for sector symmetry, for example.
The Initial value for voltage is available for all Terminal types except Voltage. This can be useful to provide a good initial guess for the nonlinear solver or to provide an initial condition for a time-dependent study. Enter an Initial value for voltage Vinit.
The Initial value for charge is available for the Circuit excitation. It specifies the initial charge on the terminal when a circuit is connected. This may improve nonlinear solver convergence or serve as an initial condition for a transient solver. Enter an Initial value for charge Qinit.
Constraint Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.
Studies and Solvers in the COMSOL Multiphysics Reference Manual
For a voltage terminal type example, see Dielectric Shielding Comparison: Application Library path ACDC_Module/Introductory_Electrostatics/dielectric_shielding_comparison.