Lumped Port
The Lumped Port feature connects a waveguide or duct inlet/outlet to a lumped representation element. This can be an Electrical Circuit, a two-port network defined through a transfer matrix, or a lumped representation of a waveguide. Basically, it couples the end of a waveguide to an exterior system that has a given lumped representation. Several representations and sources exist to describe the lumped system as well as excite the system. When using the lumped port representation, it is assumed that only plane waves propagate in the acoustic waveguide.
Port Geometry
The settings in this section ensure that the correct port area (including symmetries) is used for computing important quantities like power, volume flow, and transfer matrix elements, associated with the port
Select the Port area as Use symmetries (the default) or Selected boundaries.
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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.
The Lumped 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.
The Lumped 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.
Lumped Properties
Select the type of lumped representation connected to the port by selecting the Connection type as Circuit, Two-port (the default), or Waveguide. The selection made here influences the settings and options in the Connection Type section (see below).
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The Circuit option is used to connect the port boundary to an Electrical Circuit interface (this requires the AC/DC module). The connection is set up by adding the External I vs. U element in the circuit model and selecting the lumped port as the Electric potential, for example, Voltage from lumped port (acpr/lport1). The feature automatically introduces a unit transformation from electric to acoustic units. The classical equivalence between the voltage V (SI units: V) and the pressure p (SI unit: Pa) as well as the current I (SI unit: A) and the volume velocity Q (SI unit: m3/s) is made.
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For the Two-port option it is assumed that the port boundary is connected to a two-port system described through a transfer matrix T. See the Connection Type section for details.
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For the Waveguide option it is assumed that the port boundary is extended with a waveguide of constant and identical cross section. The connection is equivalent to the two-port as the waveguide is defined through the appropriate transfer matrix T, of a waveguide. See the Connection Type section for details.
For the Two-port and the Waveguide options also select the Exterior condition as Circuit, Ideal source (the default), Impedance, or Port. The selection made here influences what section is visible in the user interface. When Port is selected enter the Port name, similar to the Port condition. See below for a description of the options.
Two electroacoustic tutorial models that couple a circuit (lumped representation of a microspeaker) to an acoustic domain using the Lumped Port and the Circuit option are:
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Lumped Receiver Connected to Test Setup with a 0.4-cc Coupler: Application Library path Acoustics_Module/Electroacoustic_Transducers/lumped_receiver_04cc
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Lumped Receiver with Full Vibroacoustic Coupling: Application Library path Acoustics_Module/Electroacoustic_Transducers/lumped_receiver_vibroacoustic
Connection Type
This section is visible if Two-port or Waveguide is selected as the Connection type.
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For Two-port, select the Two-port representation as Acoustic (the default) or Electroacoustic. The selection indicates if the transfer matrix is from acoustic to acoustic variables or from electric to acoustic variables. The first can be used to include a transfer matrix of an acoustic subsystem, for example, extracted using the Port condition. The latter should, for example, be used if the transfer matrix represents a transducer with electric inputs and acoustic outputs.
Enter expressions, for example, calling interpolation functions that depend on frequency, for the elements of the transfer matrix T11, T12, T21, and T22.
For the Acoustic option, you can choose to invert the transfer matrix (reverse its direction) by selecting Invert transfer matrix direction. This option will invert and correct the signs of the transfer matrix T behind the scene.
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For Waveguide, select the Waveguide model as Automatic (the default) or User defined. The Automatic option will use the cross-section data and fluid properties of the boundary for the model. If User defined is selected, enter values for the Wave number k, the Specific characteristic acoustic impedance Z. For both options, enter the Waveguide length L (SI unit: m) modeled with the lumped representation.
The transfer matrix T couples the inlet (1) and outlet (2) pressure p and flow rate Q, defined in the feature, according to the following usual convention:
Source Settings
This section is visible if Ideal source is selected as the Exterior condition.
Select the Input source as Average pressure (the default) or Volume flow. Enter values for the average pressure pav,in or the volume flow Qin. These represent ideal sources equivalent to an ideal voltage or ideal current source.
Impedance Settings
This section is visible if Impedance is selected as the Exterior condition.
In this case, the lumped port is not active and an impedance condition can be applied to terminate the lumped representation. This could, for example, be the acoustic impedance of a microphone membrane. Select the Impedance model as User defined (the default), RCL, or Waveguide end impedance.
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For the User defined option select the input format as an Acoustic impedance Zac (SI unit: kg/m4·s) or an Impedance Z (SI unit: Pa·s/m). If the electroacoustic representation is used for the two-port enter the Electric impedance Z (SI unit: Ω).
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The RCL and Waveguide end impedance options have the same options as the Impedance boundary condition.
Incident Mode Settings
This section is visible if Port is selected as the Exterior condition.
With this option the exterior behavior of the lumped system is like a Port condition with only plane wave modes propagating. The system can be excited if Incident wave excitation at this port is turned On. Enter the amplitude Ain and phase ϕ of the incident wave. The units depend on the representation used. For this option, the scattering parameters acpr.S11, acpr.S21, and so on, of the system are also computed automatically.
Circuit
This section gives information about the state of coupling/connection to an Electrical Circuit interface. If the Lumped Port is not connected, the text Connect to ‘External I vs. U’ in the Electrical Circuit interface text will be displayed. Once connected, a reference with a tag to the associated External I vs. U node, in the Electrical Circuit interface, is displayed.