Studying Lumped Parameters
To study lumped parameters, use the terminal boundary or domain condition for each electrode. This condition is available in the following interfaces and the methods described in the previous section are used to calculate the lumped parameters:
•
Electrostatics. Uses a stationary study and the energy method.
•
Electric Currents. Uses a stationary or frequency domain study type using the method based on Ohm’s law.
•
Magnetic and Electric Fields (only available as boundary condition and only when the electric potential is one of the dependent variables). For the stationary study the energy method is used. For the Frequency Domain study type, the method based on Ohm’s law is used.
•
Magnetic Fields, Currents Only. Use the preset Stationary Source Sweep with Initialization study to compute lumped inductance and resistance matrices.
The lumped parameters are defined as global variables. Evaluate these from the
Derived Values
node under
Results
in the Model Builder or define 1D plot groups.
Sweep Settings and Touchstone Export
In the main node of the physics interface, activate a sweep to loop the excitation over the terminals in the model and calculate a lumped parameter matrix. For frequency domain models there is also an inner loop with a frequency sweep for each terminal and the lumped parameters are exported to a Touchstone file. The generated lumped parameters are in the form of an impedance or admittance matrix depending on the terminal settings. They must consistently be of either fixed voltage (for an admittance matrix) or fixed current type (for an impedance matrix).
Accuracy
Use reaction terms to be accurate when calculating the total current over the boundary. This is necessary for the forced voltage input property. The reaction terms (representing current or charge density) come from default information stored in the solution, which gives an exact calculation of the total fluxes on boundaries with constraints. They do not change the system of equations in any way — no special solver settings are required. The reaction terms are also stored by default. It is recommended to use forced voltage input property with reaction terms in the extraction of the lumped parameters. Lumped parameter variables based on voltage excitation are only available when reaction fluxes are included in the output. The optional current excitation performs a coupling that guarantees that the total current is equal to the specified value, although one cannot verify this without using reaction terms.