[[EM.Terrano]] has generalized the concept of '''Block''' as any object that obstructs and affects radio wave propagation. Rays hit the facets of a block and bounce off the surface of those facets or penetrate them and continue their propagation. Rays also get diffracted off the edges of these blocks.
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In [[EM.Cube]]'s [[Propagation Module]], blocks are grouped together by the type of their interaction with rays. [[EM.Cube]] currently offers three types of blocks for use in a propagation scene:
Click here to learn more about [[Block Types]].
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=== Impenetrable Surfaces For Outdoor Scenes ===
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[[File:PROP14(2).png|thumb|200px|[[Propagation Module]]'s Impenetrable Surface dialog]]
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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.
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To define a new impenetrable block group, follow these steps:
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# 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''' (ε<sub>r</sub>) and '''Electric Conductivity''' (σ), 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.
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Under an impenetrable block group, you can draw any of [[EM.Cube]]'s native solid or [[Surface Objects|surface objects]] or you can import external model files like STEP, IGES or STL. You can change the properties of an impenetrable surface. In the property dialog of the surface group, click on the table that list the properties to select and highlight a row. Then, click the '''Add/Edit''' button to open up the "Edit Layer" dialog. In this dialog, you can change the name of the material and its permittivity and electric conductivity. The box labeled "Specify Loss Tangent" is unchecked by default. If you check it, you can specify the '''Loss Tangent''' of the material, which, in turn, updates the value of electric conductivity at the center frequency of the project. You can also use [[EM.Cube]]'s Material List, which will be explained later.
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[[File:PROP23.png]]
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Figure: [[Propagation Module]]'s "Edit Layer" dialog corresponding to impenetrable surfaces.
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=== Penetrable Surfaces For Indoor Scenes ===
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[[File:PROP15(1).png|thumb|200px|[[Propagation Module]]'s Penetrable Surface dialog]]
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A typical indoor propagation scene usually involves an arrangement of walls that represent the interior of a building. The transmitters and receivers are then placed in the spaces among such walls. From the point of view of [[EM.Cube]]'s SBR simulator, walls act like thin penetrable surfaces. [[EM.Cube]] uses the "Thin Wall Approximation" to model penetrable surfaces. It assumes that rays simply penetrate a wall and exit at the same specular point on the opposite side of the wall. In other words, rays are not displaced by the walls, nor do they get trapped inside the walls (no internal reflection). This is equivalent to assuming a zero thickness for penetrable surfaces for the purpose of geometrical ray tracing, while the finite thickness of the "thin" surface is used for electromagnetic calculation of transmission coefficient. [[EM.Cube]] offers "Penetrable Surface Blocks" for the construction of rooms in indoor propagation scenes as well as modeling of hollow buildings and other structures. You can define many penetrable surface groups with arbitrary thicknesses and material properties (color, texture, permittivity and electric conductivity).
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To define a new penetrable surface group, follow these steps:
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# Right click on one of the '''Penetrable Surfaces''' item in the Navigation Tree and select '''Insert New Block...''' A dialog for setting up the wall properties opens up offering a preloaded material type (Brick) with predefined color and texture.
# Specify a name for the surface group and select a color or texture.
# The properties of a penetrable surface are identical to those of an impenetrable surface, plus an additional thickness property.
# By default, a brick wall with a thickness of 0.5 units is assumed. You can change the '''Thickness''' of the penetrable surface as well as its '''Permittivity''' ε<sub>r</sub> and '''Electric Conductivity''' σ.
# Click the '''OK''' button of the dialog to accept the changes and close it.
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Under a penetrable surface group, you can draw any of [[EM.Cube]]'s native solid or [[Surface Objects|surface objects]] or you can import external model files like STEP, IGES or STL. You can change the properties of a penetrable surface group including its default thickness. In the property dialog of the surface group, click on the table that list the properties to select and highlight a row. Then, click the '''Add/Edit''' button to open up the "Edit Layer" dialog. Similar to the case of impenetrable surfaces, from this dialog, you can change the material properties (permittivity and electric conductivity) as well as '''Thickness''', which is expressed in the project units. You can also use [[EM.Cube]]'s Material List, which will be explained later.
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[[File:PROP25.png]]
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Figure 2: [[Propagation Module]]'s "Edit Layer" dialog corresponding to penetrable surfaces.
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You can construct several thin walls and arrange them as rooms. A regular room can be built by placing four vertical wall objects together with an optional horizontal wall at the top for the ceiling. Alternatively, you may use [[EM.Cube]]'s hollow box objects or boxes with one or two capped end(s). '''Keep in mind that all the penetrable surfaces belonging to a group have the same wall thickness, which is initially set to 0.5 project units by default. Also, note that solid CAD objects belonging to a penetrable surface group are treated as air-filled hollow structures.''' The thickness of penetrable surfaces is implied and not visualized when displaying objects in the project workspace.
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=== Terrain Surfaces vs. Global Ground ===
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[[File:PROP16.png|thumb|200px|[[Propagation Module]]'s Terrain dialog]]
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A terrain surface acts as a custom, unlevel or irregular ground for your propagation scene. [[EM.Cube]]'s default global ground blocks the z < 0 half-space everywhere in the computational domain. You can simply turn off the global ground and create one or more terrain objects and place them arbitrarily in the scene. You can also import an external terrain model or file. A terrain represents an impenetrable surface with a more complex surface profile. You can have one or more terrain objects of finite extents and place them on or above the global ground.
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Terrain objects have some important differences with objects of the "Impenetrable Surface" type:
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# While impenetrable blocks can be created using any of [[EM.Cube]]'s solid or surface CAD object creation tools, terrain objects are created either using [[EM.Cube]]'s '''Terrain Generator''' or by importing an external terrain file.
# Terrain objects belong to a special type of CAD objects called "Tessellated Objects", which differ from other regular CAD [[Surface Objects|surface objects]] or [[EM.Cube]]'s polymesh surfaces.
# Terrain surfaces do not diffract impinging rays at their many small edges.
# Terrain objects affect the elevation of other objects or transmitters or receivers that are located above them.
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Just as other blocks are grouped by their color, texture and material composition, terrain objects are also grouped in a similar fashion. Before you can generate or import a new terrain object, first you have to define a terrain group and specify its color/texture and material properties. To define a new terrain group, follow these steps:
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* Right click on the '''Terrain''' item in the Navigation Tree and select '''Insert New Terrain...''' A dialog for setting up the terrain properties opens up offering a of preloaded material type (Rock) with predefined green color and no texture.
* Specify a name for the terrain group and select a color or texture.
* Similar to other blocks, you have to specify the material properties, Permittivity (ε<sub>r</sub>) and Electric Conductivity (σ), of the terrain group. Rock with ε<sub>r</sub> = 5 and σ = 0.005 S/m is the default material choice for a new terrain.
* Click the '''OK''' button of the dialog to accept the changes and close it.
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You can change the properties of a terrain surface group from its property dialog. Click on the table that list the properties to select and highlight a row. Then, click the '''Add/Edit''' button to open up the "Edit Layer" dialog, which is identical to the case of impenetrable surfaces. You can also use [[EM.Cube]]'s Material List, which will be explained later. When a new terrain type is created, its node on the Navigation Tree becomes active. Under this node you can create and add new terrain objects. When a terrain node is active for drawing, all CAD object creation tools are disabled. You have three options for creating a new terrain object, which will be described in detail in the next sections of this manual:
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# Use [[EM.Cube]]'s '''Terrain Generator'''.
# Import an external terrain file of "'''.TRN'''" type.
# Import an external terrain file of "'''.DEM'''" type.
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Click here to learn more about [[Using Terrain Generator]].
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[[File:PROP18.png|thumb|250px|[[Propagation Module]]'s Terrain Generator dialog]]
=== Importing & Exporting Terrain Models ===
Figur: An imported external terrain model.
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=== Multilayer Surface Models ===
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[[File:PROP26.png|thumb|200px|Propagation Module's Penetrable Surface Dialog showing a three-layer wall composition]]
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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.
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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''', ε<sub>r</sub> and σ. 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.
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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.
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[[File:PROP24.png]]
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Figure: [[EM.Cube]]'s material list.
=== Transferring Objects From Or To Other Modules ===