Before you begin to set up the geometry of your project, letâs quickly ensure that the project units are set up correctly. First, open up the Units Dialog box by selecting the Units button of the Simulate Toolbar (or using the keyboard shortcut Ctrl+U). Make sure the length units are Millimeters, and select OK to continue. Similarly, for frequency and bandwidth, select the Frequency button of the Simulate Toolbar (or use the keyboard shortcut Ctrl+F) to open the Frequency Dialog box. Make sure both the frequency and bandwidth are 1GHz, and select OK to continue.
[[Image:Fdtd_lec1_2a_unitsfrequency.png|450px550px|center]]
==1.2 FDTD Module Navigation==
[[Image:fdtd_lec1_5_nevigation.png|400px370px|right]] To navigate to [[FDTD Module|FDTD module]], simply select its icon from the Module Toolbar on the left side of the screen. Any module may be selected this way. Selecting the module icon changes the Navigation Tree to represent the types of objects supported by the current module. The Navigation Tree of all computational modules features To navigate to [[FDTD Module|FDTD module]], simply select its icon from the Module Toolbar on the left side of the screen. Any module may be selected this way. Selecting the module icon changes the Navigation Tree to represent the types of objects supported by the current module. The Navigation Tree of all computational modules features the following nodes: Physical Structure, Computational Domain, Discretization, Sources, and Observables.
The default view in EM.Cube is a 3D Perspective view of the project workspace. A different view can be selected by one of the 7 window selection buttons on the View Toolbar. Further, the 3D window can be split into the Top, Front, Right, and Perspective viewports by clicking on the âSplit Viewportâ button. This will display four smaller windows simultaneously, allowing you to view your structure from each of these four angles at once. Clicking the âMerge Viewportâ button, right next to the âSplit Viewportâ button, brings the split view back into a single view.
With the line tool selected, click the origin (0,0,0), and drag the mouse to start drawing a line. While still in âDraw Modeâ, press and hold the Alt button of the keyboard. This forces the drawn line to be constrained along the alternate Z-axis (normal to the default XY plane on which the mouse pointer moves). Observe the changing Length value in the dialog box as you drag the mouse back and forth. When the length reaches a value of 150 units, left-click to âlock-inâ the value. You may also left-click at any point and adjust the length by typing in a value of 150 in the objectâs property dialog.
[Image:fdtd_lec1_8_lineproprerties.png|400px500px]]
Since the center frequency of the project is 1GHz, the operating wavelength is:
For your resonant dipole to be half-wave, it can be approximated at 150mm.
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Once your drawing is complete, you can zoom to fit your stucture into the screen using the keyboard shortcut Ctrl+E or by clicking the Zoom Extents button of View Toolbar. After you have rotated or panned the view, you can always restore EM.Cubeâs standard perspective view using the keyboardâs Home Key or by clicking the Perspective View button of View Toolbar.
The boundary Conditions at the six faces of the computational domain can be set by selecting the menu item Simulate ï Computational Domain ï Boundary Conditions⦠or by right clicking on the âBoundary Conditionsâ item in the âComputational Domainâ section of the Navigation Tree. By default, EM.Cubeâs [[FDTD Module]] assumes an open-boundary physical structure. All the six boundaries default to PML, or Perfectly Matched Layer, which you are going to maintain for this tutorial lesson. But the dropdown lists allow you to also choose PEC, or a Perfect Electric Conducting boundary, or PMC, a Perfect Magnetic Conducting boundary.
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[[Image:fdtd_lec1_10_domainboundary.png|500px|center]]
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==1.5 Source Definition==
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[[Image:fdtd_lec1_11_lumpedsource.png|400px|right]] A dipole antenna can be excited using a lumped source, which is one of the simplest source types in [[FDTD Module]]. A lumped source is a voltage source in series with an internal resistance that is placed between two adjacent nodes of the FDTD mesh. To define a lumped source, right-click on the Lumped Source item in the âSourcesâ section of the Navigation Tree, and select Insert New Source⦠The Lumped Source Dialog opens up.
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A lumped source can only be placed on a line object. Additionally, the line must be parallel to one of the principal axes. The dropdown list labeled Line Object displays all the eligible lines in the project workspace. In this project, there is only one object, which is selected by default. A new lumped source is placed at the center of the host line object by default. The location of the source can be changed via the Offset parameter of the dialog. We will leave this at 75 for this tutorial, as we want to test a center-fed dipole. You can also change the direction of the lumped source.
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[[Image:fdtd_lec1_12_lumpedsourcefig.png|400px|left]] Your lumped source will have an Amplitude of 1V and a zero Phase. This means that the voltage source will excite the dipole with a modulated Gaussian pulse waveform centered at 1GHz with a frequency bandwidth of 1GHz, where the envelope of the signal reaches a maximum voltage of 1V. You will see the lumped source in the middle of the dipole, represented by an arrow pointing in the +Z direction.
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==1.6 Grid Settings & Mesh Generation==
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EM.Cubeâs [[FDTD Module]] generates a Yee mesh of your physical structure. The mesh properties can be accessed by clicking the Mesh Settings button of the Simulate Toolbar (or using the keyboard shortcut Ctrl+G or via the menu Simulate ï Discretization ï Mesh Settings). For this tutorial, accept the default value of 20 Cells/ï¬eff for Minimum Mesh Density.
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[[Image:fdtd_lec1_13_meshsetting.png|500px|center]]
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To view the mesh, click the Show/Generate Mesh button of the Simulate Toolbar (or alternatively use the keyboard shortcut Ctrl+M). For this particular project, the mesh view does not reveal much because the mesh of a vertical line object conforms to the grid. In general, the mesh view shows how the simulation engine sees your physical structure. You can also display the three mesh grid planes by right clicking on one of the three items XY Grid Plane, YZ Grid Plane, or ZX Grid Plane in the âDiscretizationâ section of the Navigation Tree and selecting Show from the contextual menu. To remove the grid planes from the project workspace, open the same contextual menu and select Hide.
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[[Image:fdtd_lec1_14_gridplane.png|500px|center]]
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==1.7 Defining Project Observables==
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[[Image:fdtd_lec1_15_fieldprobe.png|400px|right]] Project observables are output quantities that you would like to compute at the end of an FDTD simulation. By default, an FDTD time marching scheme does not generate any output data unless you define one or more project observables before you start a simulation.
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Field Probes
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The simplest observable is a Field Probe, which is used to record the field values as a function of time at a specific point inside the computational domain. To define a field probe, right click on the Field Probes item in the âObservablesâ section of the navigation Tree and selec Insert New Observable⦠In the Field Probe Dialog, select X from the dropdown list labeled Direction. This means that your probe will record the X component of electric and magnetic fields. Enter the point (5, 5, 75) as the Coordinates of the field probe. Click the OK button of the dialog to accept the changes
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[[Image:fdtd_lec1_16_fieldsensor.png|400px|right]] Field Sensors
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[[Image:fdtd_lec1_16_fieldsensor.png|400px|left]] Field sensors are are used to visualize the near fields of your structure on a plane parallel to one of the three principal planes. The field sensor planes extend across the entire computational domain. To define a field sensor, right click on the Field Sensors item in the âObservablesâ section of the Navigation Tree and select Insert New Observable⦠In the Field Sensor Dialog, enter the point (0, 0, 0) for Coordinates and select X from the dropdown list labeled Direction. This means that your field sensor plane will be the YZ plane, which passes through the dipole antenna. We would like to display the fields in the frequency domain at 1GHz. Accept the other default settings in the dialog box, and select OK to continue. A new entry Sensor_1 is added to the Navigation Tree, and the field sensor is now represented in the project workspace by a purple plane across the computational domain.
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Radiation Patterns
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To plot the radiation patterns of a radiating structure, you need to define a far field observable. A radiation box has to be established that encloses all the radiating objects. The electric and magnetic fields on the surface of this box are used to calculate the far field. By default, the radiation box is defined 0.1 free-space wavelength away from the bounding box of the geometry. To define a far field observable, right click on the Far Fields item in the Observables section of the Navigation Tree, and select Insert New Radiation Pattern⦠In general, you can accept the default values, unless a special case is being analyzed. The radiation box appears as a cyan or light blue box around your physical structure.
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[[Image:fdtd_lec1_10_domainboundary.png|500px]]
[[Image:fdtd_lec1_11_lumpedsource.png|500px]]
[[Image:fdtd_lec1_12_lumpedsourcefig.png|500px]]
[[Image:fdtd_lec1_13_meshsetting.png|500px]]
[[Image:fdtd_lec1_14_gridplane.png|500px]]
[[Image:fdtd_lec1_15_fieldprobe.png|500px]]
[[Image:fdtd_lec1_16_fieldsensor.png|500px]]
[[Image:fdtd_lec1_17_radiationpattern.png|500px]]
[[Image:fdtd_lec1_18_portdefinition.png|500px]]