The Transmission Line, Parameters Interface
The Transmission Line, Parameters () interface, found under the Radio Frequency branch () of the Model Wizard or Add Physics window, computes the per-unit-length (p.u.l.) parameters of two-conductor transmission lines, namely the series resistance R, series inductance L, shunt conductance G, shunt capacitance C, as well as characteristic impedance Zc and propagation constant γ. The interface supports only 2D geometries. The formulation is in the frequency domain.
When this physics interface is added, the following default nodes are added to the Model Builder: Dielectric, Reference Conductor, Signal Conductor, Insulation (the default boundary condition), and Initial Values. From the Physics toolbar, you can optionally add a Free Space node. You can also right-click Transmission Line, Parameters to select physics features from the context menu.
Physics-Controlled Mesh
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 checkbox 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 physics-controlled mesh automatically identifies the conductors in the physics, and applies a boundary layer mesh along the boundaries to resolve for the skin depth. Specifically, the Boundary Layers is applied to the conductor-type domains. The Boundary Layer Properties have the external boundary of the domains as Boundary selection. For the Layers, the Thickness specification is set as First layer, and the Thickness adjustment factor is set as half of the skin depth. A Free Triangular mesh type is added to the remaining domains.
In the COMSOL Multiphysics Reference Manual see the Physics-Controlled Mesh section for more information about how to define the physics-controlled mesh.
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 tlpa.
Dependent Variables
The dependent variables (field variables) are the Electric potential V (V) and the Magnetic vector potential A (Wb/m). The name can be changed but the names of fields and dependent variables must be unique within a model.
Discretization
Select the shape order for the Electric potential and the Magnetic vector potential dependent variables — Linear, Quadratic (the default), or Cubic. For more information about the Discretization section, see Settings for the Discretization Sections in the COMSOL Multiphysics Reference Manual.