[[Image:fdtd14_tn.png|thumb|320px|Geometric construction of a dielectric-coated metallic cylinder.]]
The following rules apply to the definition of materials and objects in [[EM.Tempo]]:
* Under the [[#Perfect Conductors|PEC]] category, you can define all types of solid, and surface and [[Curve Objects|curve CAD objects]].* Under the [[#Perfect Conductors|PMC]] category, you can define only define rectangle strip objects parallel to the principal planes. * Under the [[#Dielectric Materials|Dielectric]], [[#Anisotropic Materials|Anisotropic]] and [[#Dispersive Materials|Dispersive]] material categories, you can define only [[Solid Objects|solid CAD objects]].
* Under the Inhomogeneous Material category, you can only import a Cartesian ".CAR" data file.
* Under the Thin Wire category, you can only define line objects parallel to the principal axes.
[[EM.Tempo]] 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. 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 EM.Tempo's material hierarchy rule. 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:
# PEC