# '''Perfect Magnetic Conductor (PMC):''' The tangential magnetic field on the surface of this type of perfect conductor is zero. The electric and magnetic fields are assumed to vanish inside the volume of a PMC object. A PMC material is characterized by an infinite magnetic conductivity (σ<sub>m</sub> = ∞).
PEC and PMC materials do not have any constitutive material properties that you can modify except for their color or texture. Note that [[FDTD Module]]'s PMC materials are different in nature than the PMC traces you will find in EM.Cube's [[Planar Module]]. In the latter, the PMC term is applied to slot traces, which represent finite-sized cut-out objects (areas) from an infinite horizontal PEC ground plane. [[FDTD Module]]'s PMC objects, by contrast, can be arbitrarily oriented [[Surface Objects|surface objects ]] or impenetrable [[Solid Objects|solid objects ]] of finite extents.
To define a new PEC or PMC material, follow these steps:
The following rules apply to the definition of materials and objects in EM.Cube's [[FDTD Module]]:
* Under the [[#Perfect Conductors|PEC]] and [[#Perfect Conductors|PMC]] material categories, you can define all types of solid and [[Surface Objects|surface objects]].* Under the [[#Dielectric Materials|Dielectric]], [[#Anisotropic Materials|Anisotropic]] and [[#Dispersive Materials|Dispersive]] material categories, you can define only [[Solid Objects|solid objects]].* Under the [[#Perfect Conductors|PEC]] material category, you can also define [[Curve Objects|curve objects ]] such as lines, polylines, etc. to model wire structures.
EM.Cube's [[FDTD Module]] allows overlapping objects, although it is generally recommended that object overlaps be avoided in favor of clearly defined geometries and object boundaries. If two or more objects of the same material type and group overlap, they are merged using the Boolean union operation during the mesh generation process.<font color="red"><u>''' If two overlapping objects belong to two different material categories, then the material properties of the FDTD cells in the overlap region will follow the [[FDTD Module]]'s material priority rule.'''</u></font> In that case, the overlap area cells will always be regarded as having the material type of the higher priority. According to this rule, the material types are ordered from the highest priority to the lowest in the following manner:
You can move one or more selected objects to any other material group. Right click on the highlighted selection and select '''Move To > FDTD >''' from the contextual menu. This opens another sub-menu with a list of all the available material groups already defined in your [[FDTD Module]] project. Select the desired material node, and all the selected objects will move to that material group. The objects can be selected either in the project workspace, or their names can be selected from the Navigation Tree. In the case of a multiple selection from the Navigation Tree using the keyboard's '''Shift Key''' or '''Ctrl Key''', make sure that you continue to hold the keyboard's '''Shift Key''' or '''Ctrl Key''' down while selecting the "Destination" material group's name from the contextual menu.
In a similar way, you can move one or more objects from an FDTD material group to one of EM.Cube's other modules. In this case, the sub-menus of the '''Move To >''' item of the contextual menu will indicate all the EM.Cube modules that have valid groups for transfer of the selected objects. You can also move one or more objects from EM.Cube's other modules to a material group in the [[FDTD Module]]. This is especially useful when importing structure from external model files. Keep in mind that in EM.Cube you can import external objects only to '''[[CubeCAD]]'''.
[[Image:FDTD21(1).png|800px]]
===Computational Domain Settings===
[[Image:FDTD14.png|thumb|300px|[[FDTD Module]]'s Domain Settings dialog.]]
To set the solution domain of your [[FDTD Module]] project, follow these steps:
* Click the '''Domain''' [[Image:domain_icon.png]] button of the '''Simulate ''' Toolbar or select '''Menu > Simulate > Computational Domain > Domain Settings...''' or right click on the '''FDTD Domain''' item of the Navigation Tree and select '''Domain Settings...''' from the contextual menu, or use the keyboard shortcut '''Ctrl+A'''. The Domain Settings Dialog opens up, showing the current domain type selection.
By default, the domain box is shown as a wireframe box with blue lines, enclosing your structure in the project workspace. You have the option to hide or show the domain’s bounding box either by toggling the status of '''Menu > Simulate > Computational Domain > Show Domain Box''' or by right clicking the '''Computational Domain''' item of the Navigation Tree and selecting the '''Show '''or '''Hide '''item of the contextual menu and toggling their status. You can also change the color of the domain box from the Domain Settings dialog.
[[Image:FDTD14.png]]
Figure 1: [[FDTD Module]]'s Domain Settings dialog.
===Domain Boundary Conditions===
===Viewing The FDTD Mesh===
Because a full 3D FDTD mesh is difficult to visualize everywhere in the computational domain, only the discretized objects are displayed in EM.Cube's "'''Mesh View'''" mode. In particular, only the outer boundary cells on the surface of [[Solid Objects|solid objects ]] are shown. However, you can view the mesh grid planes across the domain. You can even step these planes back and forth inside the domain and view different mesh profiles of your physical structure.
To generate an FDTD mesh and view it the project workspace, follow these steps: