Most of the time, your outdoor propagation scene consists of simple buildings made of single-layer walls with standard material properties (ε<sub>r</sub> and σ). In the case of a single-layer impenetrable surface, the specular interface is an infinite dielectric half-space, which reflects the impinging rays. Single-layer penetrable surfaces, on the other hand, involve finite-thickness dielectric walls, which both reflect and transmit the incident rays. Similarly, most of your indoor propagation scenes involve simple single-layer penetrable walls with the specified material properties ε<sub>r</sub> and σ. A thin wall acts like a finite-thickness dielectric slab that both reflects and transmits incident rays. In the case of the global ground or terrain objects, only ray reflection off the ground surface is considered.
In EM.Cube's [[Propagation Module]], you can define multilayer surfaces with both reflection and transmission properties. You can define multilayer impenetrable buildings, multilayer penetrable walls, and multilayer terrain, with an arbitrary number of layers having different material compositions. You define a multilayer surface in the property dialog of a block, whether impenetrable, penetrable or terrain. In the section entitled '''Surface Type''', two options are available: '''Standard Material''' or '''User Defined Model'''. For simple multilayer walls, select the '''Standard Material''' option. You can add new layers with arbitrary thickness and material parameters to the existing layers. To insert a new layer, deselect any items in the layer list, and click the '''Add/Edit''' button to open the "Add Layer" Dialog. Here you can enter a name for the new layer and values for its '''Thickness''', eε<sub>r</sub> and sσ. You may also delete any layer by selecting and highlighting it and clicking the '''Delete''' button. You can move layers up or down using the '''Move Up''' and '''Move Down''' buttons and change the layer hierarchy.
You can also search EM.Cube's material database by clicking the '''Material''' button of "Add Layer" or "Edit Layer" dialogs. This opens the '''Materials''' Dialog. Inside the material list select and highlight any row and click the '''OK''' button. The selected material will fill out all the fields in the "Add Layer" or "Edit Layer" dialogs. Inside the Materials Dialog, you can type the few first letters of any material, and it will take you to the corresponding row of the list.