=== Impenetrable Surfaces For Outdoor Scenes ===
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 eε<sub>r</sub> = 4.4 and s σ = 0.001S001 S/m. Impinging rays are reflected from the facets of impenetrable buildings or diffracted from their edges.
To define a new impenetrable block group, follow these steps:
# Right click on either the '''Impenetrable Surfaces''' item of the Navigation Tree and select '''Insert New Block...''' A dialog for setting up the block properties opens up offering a preloaded material type (Brick) with predefined color and texture.
# Specify a name for the block group and select a color or texture.
# The electromagnetic model that determines ray-block interaction is selected under '''Specular Interface Type'''. Two options are available: '''Standard Material''' or '''User Defined Model'''. The former is the default choice and requires material properties, '''Permittivity''' (eε<sub>r</sub>) and '''Electric Conductivity''' (sσ), which are set to "Brick" by default. No magnetic properties are allowed for blocks.
# Click the '''OK''' button of the dialog to accept the changes and close it.