COMSOL 6.4 - The Electromagnetic Waves, Time Explicit Interface

The interface (

), found under the branch (

) when adding a physics interface, is used to model time-dependent electromagnetic wave propagation in linear media. The sources can be in the form of volumetric electric or magnetic currents, or electric surface currents or fields on boundaries.

This physics interface solves two first-order partial differential equations (Faraday’s law and Maxwell–Ampère’s law) for the electric and magnetic fields using the time explicit discontinuous Galerkin method.

When this physics interface is added, these default nodes are also added to the — , , and . Then, from the toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click to select physics features from the context menu.

The interface includes absorbing layers that are used to set up effective nonreflecting like boundary conditions. These features are added from the toolbar, by clicking . If COMSOL Multiphysics is not running in full-screen mode nor in a large window, is accessible in the toolbar by first clicking and then . You can also right-click in the and select from the context menu.

The physics-controlled mesh is controlled from the window for the node (if the is ). In the table in the section, find the physics interface in the column and select or clear the checkbox in the column on the same row for enabling (the default) or disabling contributions from the physics interface to the physics-controlled mesh.

When the checkbox 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 checkbox is selected for the physics interface, in the section for the physics interface below the table, choose one of the four options for the — (the default), , or . For the option , enter a suitable . For example, 1/5 of the vacuum wavelength or smaller. When 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 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.

The is the default physics interface name.

The 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 field. The first character must be a letter.

The default (for the first physics interface in the model) is ewte.

This section is available for 2D and 2D axisymmetric components.

Select the :

•

to solve for the electric field vector components in the modeling plane and one magnetic field vector component perpendicular to the plane, assuming that there is no electric field perpendicular to the plane and no magnetic field components in the plane.

•

to solve for the magnetic field vector components in the modeling plane and one electric field vector component perpendicular to the plane.

To display this section, click the button (

) and select in the dialog. In the section you can change and control the values set for the filter used in the Absorbing Layers. The values of the filter parameters defined here are used in all absorbing layers added to the model and they override the value of filter parameters enabled in the Wave Equations node. The default values of the filter parameters α, ηc, and s are set to 0.5, 0.1, and 4, respectively. Inside the absorbing layer, it is important to use a filter that is not too aggressive since this will result in spurious reflections.

	For general information about the filter see the Filter Parameters section under Wave Form PDE in the COMSOL Multiphysics Reference Manual.

Select the shape order for the dependent variables (the same order for both fields) — , , (the default), or . For more information about the section, see Settings for the Discretization Sections in the COMSOL Multiphysics Reference Manual.

The dependent variables (field variables) are for the E and for the H. The name can be changed but the names of fields and dependent variables must be unique within a model.