[[Image:FDTD1.png|thumb|200px|[[FDTD Module]]'s Navigation Tree.]]
In [[EM.Cube]]'s [[FDTD ModuleTempo]], a physical structure consists of sets of objects that are grouped together and identified by their material types. All the objects belonging to the same material group share the same color and same material properties. Materials are divided into seven categories that are listed under the '''Physical Structure''' node at the top of the navigation tree:
* [[#Perfect Conductors|Perfect Electric Conductor (PEC) Objects]]