== Excitation Sources ==
=== Gaps Sources Your 3D structure must be excited by some sort of a signal source. The excitation source you choose depends on PEC Wires and Strips === the observables you seek in your project. EM.Libera provides the following source types for exciting your physical structures:Â * '''[[Common_Excitation_Source_Types_in_EM.Cube#Lumped_.26_Gap_Sources | Strip Gap Sources]]'''* '''[[Common_Excitation_Source_Types_in_EM.Cube#Lumped_.26_Gap_Sources | Wire Gap Sources]]'''* '''[[Common_Excitation_Source_Types_in_EM.Cube#Hertzian_Dipole_Sources |Short Dipole Sources]]'''* '''[[Common_Excitation_Source_Types_in_EM.Cube#Plane_Wave_Sources | Plane Wave Sources]]'''* '''[[Hybrid_Modeling_using_Multiple_Simulation_Engines#Working_with_Huygens_Sources | Huygens Sources]]'''
A Gap is an infinitesimally narrow discontinuity that is placed on the path of the current. In EM.Libera, a gap is used to define an excitation source in the form of an ideal voltage source. Gap sources can be placed on '''Thin Wire Line''' and '''Polyline''' objects to provide excitation for the Wire MoM solver. The gap splits the wire into two lines with a an infinitesimally small spacing between them, across which the ideal voltage source is connected.
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A short dipole provides a simple way of exciting a structure in EM.Libera. A short dipole source acts like an infinitesimally small ideal current source. To define a short dipole source, follow these steps:
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Common_Excitation_Source_Types_in_EM.Cube#Hertzian_Dipole_Sources | Hertzian Dipole Sources]]'''.
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Your physical structure in EM.Libera can be excited by an incident plane wave. In particular, you need a plane wave source to compute the radar cross section of a target. The direction of incidence is defined by the θ and φ angles of the unit propagation vector in the spherical coordinate system. The default values of the incidence angles are θ = 180° and φ = 0° corresponding to a normally incident plane wave propagating along the -Z direction with a +X-polarized E-vector. [[EM.Libera]] provides the following polarization options: TMz, TEz, Custom Linear, LCPz and RCPz.
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Common_Excitation_Source_Types_in_EM.Cube#Plane_Wave_Sources | Plane Wave Sources]]'''.
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{{Note|In the spherical coordinate system, normal plane wave incidence from the top of the domain downward corresponds to θ of 180°. }}
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<table>
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<td> [[Image:MOM8.png|thumb|360px|EM.Libera's Plane Wave dialog.]] </td>
<td> [[Image:po_phys16_tn.png|thumb|360px|Illuminating a metallic sphere with an obliquely incident plane wave source.]] </td>
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[[Image:MOM7.png|thumb|360px|EM.Libera's short dipole source dialog.]]
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=== Hertzian Dipole Sources ===
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A short dipole provides a simple way of exciting a structure in EM.Libera. A short dipole source acts like an infinitesimally small ideal current source. To define a short dipole source, follow these steps:
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Common_Excitation_Source_Types_in_EM.Cube#Hertzian_Dipole_Sources | Hertzian Dipole Sources]]'''.
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=== Plane Wave Sources ===
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Your physical structure in EM.Libera can be excited by an incident plane wave. In particular, you need a plane wave source to compute the radar cross section of a target. The direction of incidence is defined by the θ and φ angles of the unit propagation vector in the spherical coordinate system. The default values of the incidence angles are θ = 180° and φ = 0° corresponding to a normally incident plane wave propagating along the -Z direction with a +X-polarized E-vector. [[EM.Libera]] provides the following polarization options: TMz, TEz, Custom Linear, LCPz and RCPz.
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[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Common_Excitation_Source_Types_in_EM.Cube#Plane_Wave_Sources | Plane Wave Sources]]'''.
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{{Note|In the spherical coordinate system, normal plane wave incidence from the top of the domain downward corresponds to θ of 180°. }}
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<table>
<tr>
<td> [[Image:MOM8.png|thumb|360px|EM.Libera's Plane Wave dialog.]] </td>
<td> [[Image:po_phys16_tn.png|thumb|360px|Illuminating a metallic sphere with an obliquely incident plane wave source.]] </td>
</tr>
</table>
== Running 3D MoM Simulations ==