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Only one port should be excited at a time if the purpose is to compute S-parameters. The S-parameters are defined as acpr.S11, acpr.S21, and so on, and can be used in postprocessing.
An evaluation group for the Scattering Coefficient exists as a Predefined Plot. When evaluating, change the Data Series Operation for the port sweep parameter (PortName) to Sum to get the proper data formatting.
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For User defined enter user defined expressions for the Mode shape pn and the Mode wave number kn (SI unit: rad/m). The modes shape will automatically be scaled before it is used in the port condition. The normalized mode shape can be visualized by plotting acpr.port1.pn (here for Port 1, and so on). Use the user defined option to enter a known analytical expression or to use the solution from The Pressure Acoustics, Boundary Mode Interface. The solutions from the boundary mode analysis can be referenced using the withsol() operator.
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The User defined option can be used to easily define a plane-wave mode. Simply enter 1 for the mode shape and acpr.k as the mode wave number.
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The Numeric port option is used for waveguide cross sections that are neither circular nor rectangular. In this case, a boundary mode problem is solved on the port face to compute the desired propagating mode. This option requires the use of a Boundary Mode Analysis step in the study. It should be placed before the Frequency Domain step. In the study, add one Boundary Mode Analysis step for each Numeric port and make sure to reference the proper Port name in the study step.
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In general for a model with losses, use the default Out-of-plane wave number option; then the wave number is taken from the Boundary Mode Analysis step. In this case, it is not possible to perform a frequency sweep in the Frequency Domain study step. Only one frequency can be used and it should correspond to the Mode analysis frequency entered in the Boundary Mode Analysis step(s). One option is to add a Parametric Sweep and define a parameter for the frequency used in both the steps. In this case, care should be taken when setting up the search criteria in the mode analysis.
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For a model without any losses, select the Computed lossless mode cutoff frequency option. In this case, a frequency sweep is possible. The Boundary Mode Analysis should only be carried out at the highest frequency in the sweep. The wave number is computed analytically for all the other frequencies.
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When the Numeric port option is used and the boundary mode analysis is run, the boundary conditions from the Pressure Acoustics model are automatically inherited in the boundary problem. For this automatic procedure, there is only support for the Sound Hard Boundary (Wall), Symmetry, Pressure, and Sound Soft conditions. If you need a more complex behavior, use the Pressure Acoustics, Boundary Mode interface in combination with the User defined port type.
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When running a frequency domain sweep, in a model that uses either the Circular or the Rectangular port options, you can get a solver warning: New constraint force nodes detected: These are not stored.
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The Circular port option is used for a port with a circular cross section. Enter the Mode number, azimuthal m and the Mode number, radial n to define the mode captured by the port. In 3D, also right-click the Port condition to add the Circular Port Reference Axis when the Circular port type is selected. The cutoff frequency of the mode can be evaluated in postprocessing using the variable acpr.port1.fc (here for Port 1, and so on).
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The Rectangular port option, only available in 3D, is used for a port with a rectangular cross section. Enter the Mode number, longest side m and the Mode number, shortest side n to define the mode captured by the port.
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The Slit port option is only valid in 2D geometries. Enter the Mode number m to define the mode captured by the port.
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The cutoff frequency of the port modes can be evaluated in postprocessing using the variable acpr.port1.fc (here for Port 1, and so on).
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When Use symmetries is selected, symmetry conditions adjacent to the port will automatically be taken into account if the Port area multiplication factor is set to Automatic (the default); if set to User defined, enter the area multiplication factor Ascale manually.
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When Selected boundaries is selected, the port will have the area of the selected boundaries, without taking any symmetry conditions into account.
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The Port condition can only be applied to connected boundaries and the boundaries should typically be coplanar. The port condition can in principle be applied to a curved continuous boundary, but care should be taken that the setup is mathematically and physically consistent.
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The Port boundary conditions should in general be placed at least one waveguide diameter from other geometry features to ensure that only a pure fully developed propagating wave exists at the port. Note also that the port condition does not treat possible evanescent waves.
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For Amplitude enter the amplitude Ain (SI unit: Pa) of the incident wave. This is in general defined as the maximum amplitude for a given mode shape.
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For Power enter the power Pin (SI unit: W) of the incident wave. This is in general defined as the RMS power of the incident wave.
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For both options enter the phase ϕ (SI unit: rad) of the incident wave. This phase contribution is multiplied with the amplitude defined by the above options. The Amplitude input can be a complex number.
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For the Circular and Rectangular options make sure to only select modes that are actually symmetric according to the symmetry planes.
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The port condition is in general not compatible with the Background Pressure Field domain feature. Combining the two will generate unphysical results if placed next to each other.
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