In EM.Cube’s [[FDTD Module]], objects are grouped together and organized by material under the “Physical Structure” node of the Naviation Tree. Since you selected no material for your line object, the first drawn object is automatically assigned a <i>PEC_1</i> material group. The default perfect electric conductor (PEC) group is set as the active material. When a material group is set as active, its name appears in bold letters, and all subsequently drawn objects will be placed under that material node. Any material group can be set as the active material by right-clicking on its name in the Navigation Tree and selecting <b>Activate</b> from the contextual menu.
==Computational Domain & Boundary Conditions==
As soon as you draw your first object in [[FDTD Module]]’s project workspace, a blue wireframe box appears which completely encloses your object. This is [[FDTD Module]]’s computational domain box. Since FDTD is a finite-domain numerical technique, it requires a computational domain of finite extents. By default, the domain box is placed a quarter free space wavelength from the largest bounding box of your physical structure. You can confirm this by opening the Domain Settings Dialog. Click the <b>Domain Settings</b> [[Image:fdtd_domainsettings.png]] button of Simulate Toolbar (or select the menu item <b>Compute → Computational Domain → Domain Settings…</b> or use the keyboard shortcut <b>Ctrl+A</b>) to bring up the domain dialog box. For the default domain type, the domain size is specified in terms of offsets along the ±X, ±Y, and ±Z directions, i.e., the distances between the largest bounding box of the geometry and all the six domain boundaries. The offsets are expressed in free space wavelengths calculated at the highest frequency of the project, which is fmax = f0 + Δf/2, where f0 is the center frequency of the project and Δf is the bandwidth.
[[Image:fdtd_lec1_10_domainboundary.png|center]]
==1.5 Source Definition==