Terminal
The Terminal node provides a boundary or domain condition for connection to external circuits, to transmission lines, or with a specified voltage or current. By specifying zero current, 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 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 Electric Currents node.
The Terminal node also enables the computation of the lumped parameter of the system, such as the impedance.
The Harmonic Perturbation subnode (it is of the exclusive type) is available from the context menu (right-click the parent node) or in the Physics toolbar, click the Attributes menu and select Harmonic Perturbation. The Harmonic Perturbation subnode only has effect if Current or Voltage are selected as terminal type. For more information see Harmonic Perturbation — Exclusive and Contributing Nodes in the COMSOL Multiphysics Reference Manual.
An operation named as 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.
Terminal
Specify the terminal’s properties. The Terminal name identifies the terminal and the variables it creates. The name should be numeric for sweeps to work properly.
Select a Terminal type — Current (the default), Voltage, Circuit, Power, Terminated (power), and Terminated (voltage).
The Circuit and Power types cannot be used together with a terminal sweep.
Select:
•
Current to specify a total current flowing from the terminal. Enter the current I0 (SI unit: A). The default is 0 A for an open circuit.
•
Voltage to specify a fixed electric potential at the terminal. Enter the value of the electric potential V0 (SI unit: V). The default is 1 V.
•
Circuit to specify a terminal connected to an Electrical Circuit interface that models an external circuit.
•
Power to specify a fixed electric power for the terminal. The power is computed as the product of the terminal current and voltage and, in the frequency domain, is the cycle-averaged power. When Power is selected:
-
Enter a Terminal power P0 (SI unit: W) to specify the input power at this terminal. The default is 1 W.
•
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.
-
Enter a Terminal power P0 (SI unit: W) to specify the input power at this terminal from the transmission line. This excitation can be toggled using a terminal sweep. The default is 1 W.
-
Select an option from the Characteristic impedance from list to define the value of the impedance — Physics interface (the default) or User defined. For Physics interface the Reference impedance Zref defined in the Settings window for the physics interface under Sweep Settings is used. For User defined enter a specific impedance Zref (SI unit: Ω) for this terminal. The default is 50 Ω.
•
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: .
Using Power excitation causes the equation system to become nonlinear. COMSOL Multiphysics automatically adjusts the solver settings when Power is selected.
Be aware that, in general, the values of the voltage and the current might not uniquely be determined by this constraint and may depend on the initial value provided for the current and voltage variables. Particularly in the frequency domain, the absolute phase of the quantities can be arbitrary. This indeterminacy can have an impact on the solution process. See Compile Equations in the COMSOL Multiphysics Reference Manual for a possible solution to this problem.
Initial Values
The initial values subsection is used to provide initial values for the internal state variables in the Terminal. These settings can be useful to provide an initial guess to the nonlinear solver or the initial value in a time-dependent study when the initial values of the other dependent variables (such as the electric potential) are computed from a separate physics or study. In most cases, the default values are appropriate.
The Initial value for voltage is available for all Terminal types except Voltage. Enter an Initial value for voltage Vinit (SI unit: V). The default is 0 V.
The Initial value for current is available for Power only. In this case, it provides an initial guess for the nonlinear solver, and should not be set to zero. The initial value provided may affect the solution. Enter an Initial value for current Iinit (SI unit: A). The default is 1 mA.
Constraint Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.