===Geometrical Rules & Material Hierarchy===
[[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 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.
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[[Image:FDTD_MAN1.png|thumb|left|420px|The geometric construction of a dielectric-coated metallic cylinder with a conformal foil.]]
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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: