=== Impenetrable Surfaces For Outdoor Scenes ===
[[File:PROP14(2).png|thumb|250px200px|[[Propagation Module]]'s Impenetrable Surface dialog]]
In outdoor propagation scenes such as "Urban Canyons", you are primarily interested in the wireless coverage in the areas among buildings. You can assume that rays bounce off the exterior walls of these buildings but do not penetrate them. In other words, you ignore the transmitted rays and assume that they are either absorbed or diffused inside the buildings. This is not an unrealistic assumption. EM.Cube offers "Impenetrable Blocks" to model buildings in outdoor propagation scenes. A penetrable block has a color or texture property as well as material properties: permittivity (e<sub>r</sub>) and conductivity (s). By default, a brick building is assumed with ε<sub>r</sub> = 4.4 and σ = 0.001 S/m. Impinging rays are reflected from the facets of impenetrable buildings or diffracted from their edges.