The Electromagnetic Waves, Transient Interface
The Electromagnetic Waves, Transient (ewt) interface (), found under the Wave Optics branch () when adding a physics interface, is used to solve a time-domain wave equation for the magnetic vector potential. The sources can be in the form of point dipoles, line currents, or incident fields on boundaries or domains. It is primarily used to model electromagnetic wave propagation in different media and structures when a time-domain solution is required — for example, for nonsinusoidal waveforms or for nonlinear media. Typical applications involve the propagation of electromagnetic pulses and the generation of harmonics in nonlinear optical media.
When this physics interface is added, these default nodes are also added to the Model BuilderWave Equation, Electric, Perfect Electric Conductor, and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and mass sources. You can also right-click Electromagnetic Waves, Transient to select physics features from the context menu.
Except where indicated, most of the settings are the same as for The Electromagnetic Waves, Frequency Domain Interface.
Physics-Controlled Mesh
The physics-controlled mesh is controlled from the Settings window for the Mesh node (if the Sequence type is Physics-controlled mesh). In the table in the Physics-Controlled Mesh section, find the physics interface in the Contributor column and select or clear the check box in the Use column on the same row for enabling (the default) or disabling contributions from the physics interface to the physics-controlled mesh.
When the Use check box for the physics interface is selected, this invokes a parameter for the maximum mesh element size in free space. The physics-controlled mesh automatically scales the maximum mesh element size as the wavelength changes in different dielectric and magnetic regions. If the model is configured by any periodic conditions, identical meshes are generated on each pair of periodic boundaries. Perfectly matched layers are built with a structured mesh, specifically, a swept mesh in 3D and a mapped mesh in 2D.
When the Use check box is selected for the physics interface, in the section for the physics interface below the table, choose one of the four options for the Maximum mesh element size control parameterUser defined (the default), Frequency, or Wavelength. For the option User defined, enter a suitable Maximum element size in free space. For example, 1/5 of the vacuum wavelength or smaller. When Frequency is selected, enter the highest frequency intended to be used during the simulation. The maximum mesh element size in free space is 1/8 in 2D and 1/5 in 3D of the vacuum wavelength for the entered frequency. For the Wavelength option, enter the smallest vacuum wavelength intended to be used during the simulation. The maximum mesh element size in free space is 1/8 in 2D and 1/5 in 3D of the entered wavelength.
The maximum mesh element sizes discussed above are used with quadratic shape functions. When linear shape functions are used, 1/2 of the maximum mesh element size for quadratic shape functions are used. Similarly, when cubic shape functions are used, the maximum mesh element size is 2.25 times the maximum mesh element size for quadratic shape functions.
The maximum mesh element size in dielectric media is equal to the maximum mesh element size in vacuum divided by the square root of the product of the relative permittivity and permeability.
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 ewt.
Components
This section is available for 2D and 2D axisymmetric components.
Select the Electric field components solved for. Select:
Three-component vector (the default) to solve using a full three-component vector for the electric field E.
Out-of-plane vector to solve for the electric field vector component perpendicular to the modeling plane, assuming that there is no electric field in the plane.
In-plane vector to solve for the electric field vector components in the modeling plane assuming that there is no electric field perpendicular to the plane.
Dependent Variables
The dependent variable (field variable) is for the Magnetic vector potential A. 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 Magnetic vector potential dependent variable — Linear, Quadratic (the default), Cubic, Quartic, Quintic, Sextic, or Septic. For more information about the Discretization section, see Settings for the Discretization Sections in the COMSOL Multiphysics Reference Manual.