[[Image:Info_icon.png|40px]] Click here for a general discussion of '''[[Defining Materials in EM.Cube]]'''.
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== Discretizing the Physical Structure ==
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[[File:PO4.png|thumb|360px|EM.Illumina's Mesh Settings dialog.]]
EM.Illumina uses a triangular surface mesh to discretize the structure of your project workspace. The mesh generating algorithm tries to generate regularized triangular cells with almost equal surface areas across the entire structure. You can control the cell size using the "Mesh Density" parameter. By default, the mesh density is expressed in terms of the free-space wavelength. The default mesh density is 10 cells per wavelength. In the Physical Optics method, the electric and magnetic surface currents, '''J''' and '''M''', are assumed to be constant on the surface of each triangular cell. On flat surfaces, the unit normal vectors to all the cells are identical. Incident plane waves or other relatively uniform source fields induce uniform PO currents on all these cells. Therefore, a high resolution mesh may not be necessary on flat surface or faces. Accurate discretization of curved objects like spheres or ellipsoids, however, requires a high mesh density.
Since EM.Illumina is a surface simulator, only the exterior surface of solid CAD objects is discretized, as the interior volume is not taken into account in a PO analysis. By contrast, surface CAD objects are assumed to be double-sided. In other words, the default PO mesh of a surface object consists of coinciding double cells, one representing the upper or positive side and the other representing the lower or negative side. This may lead to a very large number of cells. EM.Illumina's mesh generator has settings that allow you to treat all mesh cells as double-sided or all single-sided. You can do that in the Mesh Settings dialog by checking the boxes labeled '''All Double-Sided Cells''' and '''All Single-Sided Cells'''. This is useful when your project workspace contains well-organized and well-oriented surface CAD objects only. In the single-sided case, it is very important that all the normals to the cells point towards the source. Otherwise, your surfaces fall in the shadow region, and no currents will be computed on them. By checking the box labeled '''Reverse Normal''', you instruct EM.Illumina to reverse the direction of the normal vectors globally at the surface of all the cells.
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Mesh_Generation_Schemes_in_EM.Cube#Working_with_Mesh_Generator | Working with Mesh Generator ]]'''.
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[[Image:Info_icon.png|40px]] Click here to learn more about EM.Illumina's '''[[Mesh_Generation_Schemes_in_EM.Cube#The_Triangular_Surface_Mesh_Generator | Triangular Surface Mesh Generator ]]'''.
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<table>
<tr>
<td> [[Image:POShip1.png|thumb|600px|Geometry of a metallic battleship model with a short horizontal dipole radiator above it.]] </td>
</tr>
<tr>
<td> [[Image:POShip2.png|thumb|600px|Trinagular surface mesh of the metallic battleship model.]] </td>
</tr>
</table>
== Excitation Sources ==
</tr>
</table>
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== Running PO Simulations ==
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=== EM.Illumina's Simulation Modes ===
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[[File:PO27.png|thumb|400px|EM.Illumina's Simulation Run dialog.]]
[[File:PO28.png|thumb|350px|EM.Illumina's Simulation Engine Settings dialog.]]
Once you have set up your structure in EM.Illumina, have defined sources and observables and have examined the quality of the structure's mesh, you are ready to run a Physical Optics simulation. EM.Illumina offers five simulation modes:
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{| class="wikitable"
|-
! scope="col"| Simulation Mode
! scope="col"| Usage
! scope="col"| Number of Engine Runs
! scope="col"| Frequency
! scope="col"| Restrictions
|-
| style="width:120px;" | Single-Frequency Analysis
| style="width:270px;" | Simulates the physical structure "As Is"
| style="width:80px;" | Single run
| style="width:250px;" | Runs at the center frequency fc
| style="width:80px;" | None
|-
| style="width:120px;" | Frequency Sweep
| style="width:270px;" | Varies the operating frequency of the PO solver
| style="width:80px;" | Multiple runs
| style="width:250px;" | Runs at a specified set of frequency samples
| style="width:80px;" | None
|-
| style="width:120px;" | Parametric Sweep
| style="width:270px;" | Varies the value(s) of one or more project variables
| style="width:80px;" | Multiple runs
| style="width:250px;" | Runs at the center frequency fc
| style="width:80px;" | None
|-
| style="width:120px;" | Optimization
| style="width:270px;" | Optimizes the value(s) of one or more project variables to achieve a design goal
| style="width:80px;" | Multiple runs
| style="width:250px;" | Runs at the center frequency fc
| style="width:80px;" | None
|-
| style="width:120px;" | HDMR Sweep
| style="width:270px;" | Varies the value(s) of one or more project variables to generate a compact model
| style="width:80px;" | Multiple runs
| style="width:250px;" | Runs at the center frequency fc
| style="width:80px;" | None
|}
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You can set the simulation mode from EM.Illumina's "Simulation Run Dialog". A single-frequency analysis is a single-run simulation. All the other simulation modes in the above list are considered multi-run simulations. If you run a simulation without having defined any observables, no data will be generated at the end of the simulation. In multi-run simulation modes, certain [[parameters]] are varied and a collection of simulation data files are generated. At the end of a sweep simulation, you can graph the simulation results in EM.Grid or you can animate the 3D simulation data from the navigation tree.
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=== Running A Single-Frequency PO Analysis ===
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To open EM.Illumina's Simulation Run dialog, click the '''Run''' [[File:run_icon.png]] button of the '''Simulate Toolbar''' or select '''Menu > Simulate > Run...'''or use the keyboard shortcut {{key|Ctrl+R}}. To start the simulation click the {{key|Run}} button of this dialog. Once the PO simulation starts, a new dialog called '''Output Window''' opens up that reports the various stages of PO simulation, displays the running time and shows the percentage of completion for certain tasks during the PO simulation process. A prompt announces the completion of the PO simulation. At this time, [[EM.Cube]] generates a number of output data files that contain all the computed simulation data. These include current distributions, near field data, far field radiation pattern data as well bi-static or mono-static radar cross sections (RCS) if the structure is excited by a plane wave source.
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=== Setting The Numerical Parameters ===
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Before you run a PO simulation, you can change some of the PO simulation engine settings. While in the EM.Illumina's '''Simulation Run Dialog''', click the '''Settings''' button next to the '''Select Engine''' dropdown list. In the Physical Optics Engine Settings Dialog, there are two options for '''Solver Type''': '''Iterative''' and '''GOPO'''. The default option is Iterative. The GOPO solver is a zero-order PO simulator that uses Geometrical Optics (GO) to determine the lit and shadow cells in the structure's mesh. For the termination of the IPO solver, there are two options: '''Convergence Error''' and '''Maximum Number of Iterations'''. The default Termination Criterion is based on convergence error, which has a default value of 0.1 and can be changed to any desired accuracy. The convergence error is defined as the L2 norm of the normalized residual error in the combined '''J/M''' current solution of the entire discretized structure from one iteration to the next. Note that for this purpose, the magnetic currents are scaled by η<sub>0</sub> in the residual error vector.
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You can also use higher- or lower-order integration schemes for the calculation of field integrals. [[EM.Cube]]'s PO simulation engine uses triangular cells for the mesh of the physical surface structures and rectangular cells for discretization of Huygens sources and surfaces. For integration of triangular cells, you have three options: '''7-Point Quadrature''', '''3-Point Quadrature''' and '''Constant'''. For integration of rectangular cells, too, you have three options: '''9-Point Quadrature''', '''4-Point Quadrature''' and '''Constant'''.
== Working with PO Simulation Data ==
</tr>
</table>
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== Discretizing the Physical Structure ==
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[[File:PO4.png|thumb|360px|EM.Illumina's Mesh Settings dialog.]]
EM.Illumina uses a triangular surface mesh to discretize the structure of your project workspace. The mesh generating algorithm tries to generate regularized triangular cells with almost equal surface areas across the entire structure. You can control the cell size using the "Mesh Density" parameter. By default, the mesh density is expressed in terms of the free-space wavelength. The default mesh density is 10 cells per wavelength. In the Physical Optics method, the electric and magnetic surface currents, '''J''' and '''M''', are assumed to be constant on the surface of each triangular cell. On flat surfaces, the unit normal vectors to all the cells are identical. Incident plane waves or other relatively uniform source fields induce uniform PO currents on all these cells. Therefore, a high resolution mesh may not be necessary on flat surface or faces. Accurate discretization of curved objects like spheres or ellipsoids, however, requires a high mesh density.
Since EM.Illumina is a surface simulator, only the exterior surface of solid CAD objects is discretized, as the interior volume is not taken into account in a PO analysis. By contrast, surface CAD objects are assumed to be double-sided. In other words, the default PO mesh of a surface object consists of coinciding double cells, one representing the upper or positive side and the other representing the lower or negative side. This may lead to a very large number of cells. EM.Illumina's mesh generator has settings that allow you to treat all mesh cells as double-sided or all single-sided. You can do that in the Mesh Settings dialog by checking the boxes labeled '''All Double-Sided Cells''' and '''All Single-Sided Cells'''. This is useful when your project workspace contains well-organized and well-oriented surface CAD objects only. In the single-sided case, it is very important that all the normals to the cells point towards the source. Otherwise, your surfaces fall in the shadow region, and no currents will be computed on them. By checking the box labeled '''Reverse Normal''', you instruct EM.Illumina to reverse the direction of the normal vectors globally at the surface of all the cells.
Â
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Mesh_Generation_Schemes_in_EM.Cube#Working_with_Mesh_Generator | Working with Mesh Generator ]]'''.
Â
[[Image:Info_icon.png|40px]] Click here to learn more about EM.Illumina's '''[[Mesh_Generation_Schemes_in_EM.Cube#The_Triangular_Surface_Mesh_Generator | Triangular Surface Mesh Generator ]]'''.
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<table>
<tr>
<td> [[Image:POShip1.png|thumb|600px|Geometry of a metallic battleship model with a short horizontal dipole radiator above it.]] </td>
</tr>
<tr>
<td> [[Image:POShip2.png|thumb|600px|Trinagular surface mesh of the metallic battleship model.]] </td>
</tr>
</table>
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== Running PO Simulations ==
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=== EM.Illumina's Simulation Modes ===
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[[File:PO27.png|thumb|400px|EM.Illumina's Simulation Run dialog.]]
[[File:PO28.png|thumb|350px|EM.Illumina's Simulation Engine Settings dialog.]]
Once you have set up your structure in EM.Illumina, have defined sources and observables and have examined the quality of the structure's mesh, you are ready to run a Physical Optics simulation. EM.Illumina offers five simulation modes:
Â
{| class="wikitable"
|-
! scope="col"| Simulation Mode
! scope="col"| Usage
! scope="col"| Number of Engine Runs
! scope="col"| Frequency
! scope="col"| Restrictions
|-
| style="width:120px;" | Single-Frequency Analysis
| style="width:270px;" | Simulates the physical structure "As Is"
| style="width:80px;" | Single run
| style="width:250px;" | Runs at the center frequency fc
| style="width:80px;" | None
|-
| style="width:120px;" | Frequency Sweep
| style="width:270px;" | Varies the operating frequency of the PO solver
| style="width:80px;" | Multiple runs
| style="width:250px;" | Runs at a specified set of frequency samples
| style="width:80px;" | None
|-
| style="width:120px;" | Parametric Sweep
| style="width:270px;" | Varies the value(s) of one or more project variables
| style="width:80px;" | Multiple runs
| style="width:250px;" | Runs at the center frequency fc
| style="width:80px;" | None
|-
| style="width:120px;" | Optimization
| style="width:270px;" | Optimizes the value(s) of one or more project variables to achieve a design goal
| style="width:80px;" | Multiple runs
| style="width:250px;" | Runs at the center frequency fc
| style="width:80px;" | None
|-
| style="width:120px;" | HDMR Sweep
| style="width:270px;" | Varies the value(s) of one or more project variables to generate a compact model
| style="width:80px;" | Multiple runs
| style="width:250px;" | Runs at the center frequency fc
| style="width:80px;" | None
|}
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You can set the simulation mode from EM.Illumina's "Simulation Run Dialog". A single-frequency analysis is a single-run simulation. All the other simulation modes in the above list are considered multi-run simulations. If you run a simulation without having defined any observables, no data will be generated at the end of the simulation. In multi-run simulation modes, certain [[parameters]] are varied and a collection of simulation data files are generated. At the end of a sweep simulation, you can graph the simulation results in EM.Grid or you can animate the 3D simulation data from the navigation tree.
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=== Running A Single-Frequency PO Analysis ===
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To open EM.Illumina's Simulation Run dialog, click the '''Run''' [[File:run_icon.png]] button of the '''Simulate Toolbar''' or select '''Menu > Simulate > Run...'''or use the keyboard shortcut {{key|Ctrl+R}}. To start the simulation click the {{key|Run}} button of this dialog. Once the PO simulation starts, a new dialog called '''Output Window''' opens up that reports the various stages of PO simulation, displays the running time and shows the percentage of completion for certain tasks during the PO simulation process. A prompt announces the completion of the PO simulation. At this time, [[EM.Cube]] generates a number of output data files that contain all the computed simulation data. These include current distributions, near field data, far field radiation pattern data as well bi-static or mono-static radar cross sections (RCS) if the structure is excited by a plane wave source.
Â
=== Setting The Numerical Parameters ===
Â
Before you run a PO simulation, you can change some of the PO simulation engine settings. While in the EM.Illumina's '''Simulation Run Dialog''', click the '''Settings''' button next to the '''Select Engine''' dropdown list. In the Physical Optics Engine Settings Dialog, there are two options for '''Solver Type''': '''Iterative''' and '''GOPO'''. The default option is Iterative. The GOPO solver is a zero-order PO simulator that uses Geometrical Optics (GO) to determine the lit and shadow cells in the structure's mesh. For the termination of the IPO solver, there are two options: '''Convergence Error''' and '''Maximum Number of Iterations'''. The default Termination Criterion is based on convergence error, which has a default value of 0.1 and can be changed to any desired accuracy. The convergence error is defined as the L2 norm of the normalized residual error in the combined '''J/M''' current solution of the entire discretized structure from one iteration to the next. Note that for this purpose, the magnetic currents are scaled by η<sub>0</sub> in the residual error vector.
Â
You can also use higher- or lower-order integration schemes for the calculation of field integrals. [[EM.Cube]]'s PO simulation engine uses triangular cells for the mesh of the physical surface structures and rectangular cells for discretization of Huygens sources and surfaces. For integration of triangular cells, you have three options: '''7-Point Quadrature''', '''3-Point Quadrature''' and '''Constant'''. For integration of rectangular cells, too, you have three options: '''9-Point Quadrature''', '''4-Point Quadrature''' and '''Constant'''.
<p> </p>