=== Moving Objects Between Groups & Modules ===
By default, the last PEC group that was defined is active. The current active group is always listed in bold letters in the Navigation Tree. All the new objects are inserted under the current active group. A group can be activated with a right click on its entry in the Navigation Tree and then selecting the '''Active''' item of the contextual menu. You can move one or more selected objects to any desired PEC group. Right click on the highlighted selection and select '''Move To [[File:larrow_tn.png]] MoM3D [[File:larrow_tn.png]]''' from the contextual menu. This opens another sub-menu with a list of all the available PEC groups already defined in the [[PO Module]]. Select the desired PEC group, and all the selected objects will move to that group. The objects can be selected either in the project workspace, or their names can be selected from the Navigation Tree. In the latter case, make sure that you hold the keyboard's '''Shift Key''' or '''Ctrl Key''' down while selecting a PEC group's name from the contextual menu. In a similar way, you can move one or more objects from a Physical Optics PEC group to EM.CUBE's other modules. In this case, the sub-menus of the''' Move To [[File:larrow_tn.png]]''' item of the contextual menu will indicate all the EM.CUBE modules that have valid groups for transfer of the select objects.
=== 3D MoM Mesh Types ===
# Verifying the mesh.
The commercial release of EM.CUBE's [[MoM3D Module]] provides a Wire MoM solver. In this simulation engine, all the metallic objects are discretized as a wire-frame structure. Wires, line and curves are discretized as polylines made up of small linear cells (segments).Surface and [[Solid Objects|solid objects ]] are discretized as a wire-frame mesh with triangular cells. The MoM3D mesh generator meshes the wires based on a specified mesh sampling rate expressed in cells/&lambda<sub>0</sub>. Curves are first polygonized and converted into '''Polyline''' Objects, whose edge lengths follow the specified mesh sampling rate. In the case of [[Solid Objects|solid objects]], only their surface and faces are discretized using a triangular wireframe mesh, which is regarded as a grid of interconnected wires. Two algorithms are offered for generation of a triangular wireframe mesh. The default algorithm is '''Regular Wireframe'''. This mesh generator creates wireframe elements that have almost equal edge lengths. The other algorithm is '''Structured Wireframe''', which usually creates a very structured wireframe with a large number of aligned wireframe elements.
To view the [[MoM3D Module]]'s wire-frame mesh, click on the [[File:mesh_tool_tn.png]] button of the '''Compute Toolbar''' or select '''Menu [[File:larrow_tn.png]] Compute [[File:larrow_tn.png]] Discretization [[File:larrow_tn.png]] Shoe Mesh''' or use the keyboard shortcut '''Ctrl+M'''. When the wire-frame mesh is displayed in the Project Workspace, EM.CUBE's mesh view mode is enabled. In this mode, you can perform view operations like rotate view, pan, zoom, etc. However, you cannot select or move or edit objects. While the mesh view is enabled, the '''Show Mesh''' [[File:mesh_tool.png]] button remains depressed. To get back to the Normal View mode, click this button one more time, or deselect '''Menu [[File:larrow_tn.png]] Compute [[File:larrow_tn.png]] Discretization [[File:larrow_tn.png]] Show Mesh''' to remove its check mark or simply click the '''Esc Key''' of the keyboard."Show Mesh" generates a new mesh and displays it if there is none in the memory, or it simply displays an existing mesh in the memory. This is a useful feature because generating a wire-frame mesh may take a long time depending on the complexity and size of objects. If you change the structure or alter the mesh settings, a new mesh is always generated. You can ignore the mesh in the memory and force EM.CUBE to generate a mesh from the ground up by selecting '''Menu [[File:larrow_tn.png]] Compute [[File:larrow_tn.png]] Discretization [[File:larrow_tn.png]] Regenerate Mesh''' or by right clicking on the '''3-D Mesh''' item of the Navigation Tree and selecting '''Regenerate''' from the contextual menu.
=== Customizing the Mesh ===
To set the wire-frame mesh properties, click on the [[File:mesh_tool_tn.png]] button of the '''Compute Toolbar''' or select '''Menu [[File:larrow_tn.png]] Compute [[File:larrow_tn.png]] Discretization [[File:larrow_tn.png]] Mesh Settings...'''or right click on the '''3-D Mesh''' item in the '''Discretization''' section or the Navigation Tree and select '''Mesh Settings...''' from the contextual menu. The MoM3D Mesh Settings Dialog opens up. You can change the mesh generation algorithm from the drop-down list labeled '''Mesh Type''' and select one of the two options: '''Regular Wireframe''' or '''Structured Wireframe'''. You can also set the '''Mesh Sampling Rate''', whose default value is 20 Cells/λ<sub>0</sub>.By default, [[Surface Objects|surface objects ]] or solids are wire-framed at the mesh cell size. Therefore, each wire segment of the wire-frame mesh contains one cell. Another parameter that can affect the shape of the mesh especially in the case of [[Solid Objects|solid objects ]] is the '''Curvature Angle Tolerance'''. This parameter expressed in degrees determines the apex angle of the triangular cells of the structured mesh. Lower values of the angle tolerance will results in more pointed triangular cells.
[[File:wire_pic4.png]]
=== Mesh of Connected Objects ===
All the [[Solid Objects|solid objects ]] belonging to the same PEC group are merged together using the Boolean union operation before meshing. If your structure contains attached, interconnected or overlapping [[Solid Objects|solid objects]], their internal common faces are removed and only the surface of the external faces is meshed. Similarly, all the [[Surface Objects|surface objects ]] belonging to the same PEC group are merged together before meshing. However, following EM.CUBE's union rules, a solid and a surface object cannot not be "unioned" together. Therefore, their meshes will not connect even if the two objects belong to the same PEC group.
You can connect a line object to a touching surface. To connect lines to surfaces and allow for current continuity, you must make sure that the box labeled '''Connect Lines to Touching Surfaces''' is checked in the '''Mesh Settings Dialog'''. If the end of a line lies on a flat surface, EM.CUBE will detect that and create the connection automatically. However, this may not always be the case if the surface is not flat and has curvature. In such cases, you have to specifically instruct EM.CUBE to enforce the connection. An example of this case is shown in the figure below.
* In the '''Direction Unit Vector''' section, you can specify the orientation of the short dipole by setting values for the components '''uX''', '''uY''', and '''uZ''' of the dipole's unit vector. The default values correspond to a vertical (Z-directed) short dipole. The dialog normalizes the vector components upon closure even if your component values do not satisfy a unit magnitude.
When you simulate a wire structure in the [[MoM3D Module]], you can define a '''Current Distribution Observable''' in your project. This is used not only to visualize the current distribution in the project workspace but also to save the current solution into an ASCII data file. This data file is called "MoM.IDI" by default and has a '''.IDI''' file extension. The current data are saved as line segments representing each of the wire cells together with the complex current at the center of each cell. In the [[MoM3D Module]], you can import the current data from an existing '''.IDI''' file to serve as a set of short dipoles for excitation. To import a wire current solution, right click on '''Short Dipoles''' item in the '''Sources''' section of the Navigation Tree and select '''Import Dipole Source...''' from the contextual menu. This opens up the standard Windows Open dialog with the file type set to '''.IDI'''. Browse your folders to find the right current data file. Once you find it, select it and click the '''Open''' button of the dialog. This will create as many short dipole sources on the [[PO Module]]'s Navigation Tree as the total number of mesh cells in the Wire MoM solution. From this point on, each of the imported dipoles behave like a regular short dipole source. You can open the property dialog of each individual source and modify its parameters.
[[File:wire_pic17.png]]
=== Visualizing Wire Current Distributions ===
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[[File:wire_pic25.png|thumb|300px|[[MoM3D Module]]'s current distribution dialog]]
At the end of a MoM3D simulation, EM.CUBE's Wire MoM engine generates a number of output data files that contain all the computed simulation data. The main output data are the current distributions and far fields. You can easily examine the 3-D color-coded intensity plots of current distributions in the Project Workspace. Current distributions are visualized on all the wires and the magnitude and phase of the electric currents are plotted for all the PEC objects. In order to view these currents, you must first define current sensors before running the Wire MoM simulation. To do this, right click on the '''Current Distributions''' item in the '''Observables''' section of the Navigation Tree and select '''Insert New Observable...'''. The Current Distribution Dialog opens up. Accept the default settings and close the dialog. A new current distribution node is added to the Navigation Tree. Unlike the [[Planar Module]], in the [[MoM3D Module]] you can define only one current distribution node in the Navigation Tree, which covers all the PEC object in the Project Workspace. After a Wire MoM simulation is completed, new plots are added under the current distribution node of the Navigation Tree. Separate plots are produced for the magnitude and phase of the linear wire currents. The magnitude maps are plotted on a normalized scale with the minimum and maximum values displayed in the legend box. The phase maps are plotted in radians between -π and π.
Current distribution maps are displayed with some default settings and options. You can customize the individual maps (total, magnitude, phase, etc.). To do so, open the '''Output Plot Settings Dialog''' by right clicking on the specific plot entry in the Navigation Tree and selecting '''Properties...''' or by double clicking on the surface of the plot's legend box. Two '''scale''' options are available: '''Linear''' and '''dB'''. With the '''Linear''' (default) option selected, the current value is always normalized to the maximum total current in that plane, and the normalized scale is mapped between the minimum and maximum values. If the '''dB''' option is selected, the normalized current is converted to dB scale. The plot limits (bounds) can be set individually for every current distribution plot. In the '''Limits''' section of the plot's property dialog, you see four options: '''Default''', '''User Defined''', '''95% Conf.''' and '''95% Conf.'''. Select the user defined option and enter new values for the '''Lower''' and '''Upper''' limits. The last two options are used to remove the outlier data within the 95% and 99% confidence intervals, respectively. In other words, the lower and upper limits are set to ? ± 1.96? and ? ± 2.79? , respectively, assuming a normal distribution of the data. Three color maps are offered: '''Default''', '''Rainbow''' and '''Grayscale'''. You can hide the legend box by deselecting the box labeled '''Show Legend Box'''. You can also change the foreground and background colors of the legend box.
[[File:wire_pic25.png]] The [[MoM3D Module]]'s current distribution dialog. [[File:wire_pic26_tn.png|400px]] [[File:wire_pic27_tn.png|400px]]
Figure: A monopole antenna connected above a PEC plate and its current distribution with the default plot settings.
[[File:wire_pic28.png|360px]] [[File:wire_pic29_tn.png|440px]]
Figure: The output plot settings dialog, and the current distribution of the monopole-plate structure with a user defined upper limit.
=== Scattering Parameters and Port Characteristics ===
[[File:wire_pic23.png]] [[File:po_phys54.png]]
The [[PO Module]]'s run simulation dialog with angular sweep selected and the angle settings dialog.
In a parametric sweep, one or more user defined [[variables]] are varied at the same time over their specified ranges. This creates a parametric space with the total number of samples equal to the product of the number of samples for each variable. The user defined [[variables]] are defined using EM.CUBE's '''[[Variables]] Dialog'''. For a description of EM.CUBE [[variables]], please refer to the [[CubeCAD|CUBECAD ]] manual or the "Parametric Sweep" sections of the FDTD or [[Planar Module]] manuals.
=== Animation of MoM3D Data ===