[[Image:FDTD1.png|thumb|250px|[[FDTD Module]]'s Navigation Tree.]]
In Your physical structure in EM.Tempo, a physical structure consists of sets can be made up of several geometric objects that are grouped together and identified by with different material compositions. EM.Tempo groups your geometric objects in the project workspace based on their material typestype. All the objects belonging to the same material group share the same color and same material properties. Materials EM.Tempo's material types are divided into seven categories that are listed under the '''Physical Structure''' node at the top of the navigation tree (click on each type to learn more about it):
* '''[[Defining_Materials_in_EM.Cube#Perfect_Electric_Conductors_.26_Metal_Traces |Perfect Electric Conductor (PEC) Objects]]'''
* '''[[Defining_Materials_in_EM.Cube#Thin_Wires |Thin Wires]]'''
Under each material nodein the navigation tree, you can create new material groups of the same type/category but with different properties (such as color, texture, or electric and magnetic constitutive [[parameters]]). These material groups are used to organize both the CAD geometric objects you draw in the project workspace or and those you import from external CAD model files.
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Defining_Materials_in_EM.Cube#Defining_a_New_Material_Group | Defining a New Material Group]]'''.