== Constructing the Physical Structure ==
=== Defining Groups Of [[Image:wire_pic1.png|thumb|350px|EM.Libera's Navigation Tree.]] In EM.Libera, you can create three different types of objects:Â * Perfect Electric Conductor (PEC ) Objects* Thin Wires* Dielectric Objects ===
[[Image:wire_pic1.png|thumb|350px|EM.Libera's Navigation Tree.]]
EM.Libera features two different simulation engines: Wire MoM and Surface MoM. Both simulation engines can handle metallic structures. The Wire MoM engine models metallic objects as perfect electric conductor (PEC) wireframe structures, while the Surface MoM engine treats them as PEC surfaces. The PEC objects can be lines, curves, surfaces or solids. All the PEC objects are created under the '''PEC''' node in the '''Physical Structure''' section of the Navigation Tree. Objects are grouped together by their color. You can insert different PEC groups with different colors. A new PEC group can be defined by simply right clicking on the '''PEC''' item in the Navigation Tree and selecting '''Insert New PEC...''' from the contextual menu. A dialog for setting up the PEC properties opens up. From this dialog you can change the name of the group or its color. In EM.Libera, PEC objects have an additional property, which is '''Wire Radius''' expressed in project units. This parameter is used in conjunction with Pocklington's integral equation for wire objects only. The line and [[Curve Objects|curve objects]] you draw in the project workspace are not displayed as cylinders with the specified radius.
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=== Defining Dielectric Objects ===
Of EM.Libera's two simulation engines, only the Surface MoM solver can handle dielectric objects. Dielectric objects are created under the '''Dielectric''' node in the '''Physical Structure''' section of the Navigation Tree. They are grouped together by their color and material properties. You can insert different dielectric groups with different colors and different permittivity e<sub>r</sub> and electric conductivity s. Note that a PEC object is the limiting cases of a lossy dielectric material when σ → ∞.
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To define a new Dielectric group, follow these steps:
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* Right click on the '''Dielectric''' item of the Navigation Tree and select '''Insert New Dielectric...''' from the contextual menu.
* Specify a '''Label''', '''Color''' (and optional Texture) and the electromagnetic properties of the dielectric material to be created: '''Relative Permittivity''' (e<sub>r</sub>) and '''Electric Conductivity''' (s).
* You may also choose from a list of preloaded material types. Click the button labeled '''Material''' to open [[EM.Cube]]'s Materials dialog. Select the desired material from the list or type the first letter of a material to find it. For example, typing '''V''' selects '''Vacuum''' in the list. Once you close the dialog by clicking '''OK''', the selected material properties fill the parameter fields automatically.
* Click the '''OK''' button of the dielectric material dialog to accept the changes and close it.
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Defining Materials in EM.Cube]]'''.
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Defining_Materials_in_EM.Cube#Defining_a_New_Material_Group | Defining a New Material Group]]'''.
Once a new surface object group node has been created on the navigation tree, it becomes the "Active" surface group of the project workspace, which is always listed in bold letters. When you draw a new CAD object such as a Box or a Sphere, it is inserted under the currently active surface typegroup. There is only one surface object group that is active at any time. Any surface object type can be made active by right clicking on its name in the navigation tree and selecting the '''Activate''' item of the contextual menu. It is recommended that you first create surface object groups, and then draw new CAD objects under the active surface object group. However, if you start a new [[EM.IlluminaLibera]] project from scratch, and start drawing a new object without having previously defined any surface object groups, a new default PEC surface object group is created and added to the navigation tree to hold your new CAD object.
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Defining_Materials_in_EM.Cube#Moving_Objects_among_Material_Groups | Moving Objects among Material Groups]]'''.