Sometimes taking advantage of [[FDTD Module]]'s material priority rule makes construction of complex objects easier. For example, a dielectric coated metallic cylinder can be modeled by two concentric cylinders: an inner PEC of smaller radius and an outer dielectric of larger radius as shown in the illustration below. The portion of the dielectric cylinder that overlaps the inner PEC cylinder is ignored by the FDTD engine because the PEC cylinder takes precedence over the dielectric in the material hierarchy. Alternatively, you can model the same structure by an inner solid PEC cylinder enclosed by an outer hollow pipe-shaped dielectric cylinder. The hollow solid can be built by extruding a planar ring or by subtracting two concentric cylinders. The first configuration utilizing material hierarchy is, of course, much easier to construct.
[[Image:{{isoimg|fdtd14_tn.png]]Â Figure 1: |Geometric construction of a dielectric-coated metallic cylinder.}}
===Moving Objects Among Material Groups===