Two-port Representation Research Articles

Unified Expression of the Conjugate Image Impedances for Two-port Representations

Unified Expression of the Conjugate Image Impedances for Two-port Representations

Acoustic Modeling of Charge Air Coolers

The necessity of reducing CO2 emissions has lead to an increased number of passenger cars that utilize turbocharging to maintain performance when the internal combustion (IC) engines are downsized. Charge air coolers (CACs) are used on turbocharged engines to enhance the overall gas exchange efficiency. Cooling of charged air increases the air density and thus the volumetric efficiency and also increases the knock margin (for petrol engines). The acoustic properties of charge coolers have so far not been extensively treated in the literature. Since it is a large component with narrow flow passages, it includes major resistive as well as reactive properties. Therefore, it has the potential to largely affect the sound transmission in air intake systems and should be accurately considered in the gas exchange optimization process. In this paper, a frequency domain acoustic model of a CAC for a passenger car is presented. The cooler consists of two conical volumes connected by a matrix of narrow ducts where the cooling of the air takes place. A recently developed model for sound propagation in narrow ducts that takes into account the attenuation due to thermoviscous boundary layers and interaction with turbulence is combined with a multiport representation of the tanks to obtain an acoustic two-port representation where flow is considered. The predictions are compared with experimental data taken at room temperature and show good agreement. Sound transmission loss increasing from 5 to over 10 dB in the range 50–1600 Hz is demonstrated implying good noise control potential.

Indirect acoustic impedance eduction in presence of flow based on an analytical two-port formulation

In order to assess the performance of advanced acoustic absorbing materials the acoustic impedance should be determined with high accuracy, especially, in presence of a grazing flow. This paper presents an analytical methodology for the grazing flow acoustic impedance eduction, based on a two-port representation of an acoustic system. This procedure is dedicated to the frequency range below the cut-on frequency of the transversal duct modes and its major appeal refers to a reduced number of microphones and the experimental rig simplicity. The methodology is verified by comparison with acoustic finite element simulations. Experiments are performed on two liner configurations and the educed impedance is compared with reference results obtained with a different approach at another test rig, and shows good agreement. A sensitivity analysis on the influence of the input parameters is carried out showing the influence of the rigid-/impedance wall transition effects, flow Mach number, number of microphones and microphone positioning accuracy.

Simple Approach to Predict Near Field Electromagnetic Interference in SMPS Using the Induced EMF Method

The electromagnetic interference generated by a switched-mode power supply on a victim circuit is analysed representing their electromagnetic field coupling by two-port networks. The essential electromagnetic interference sources of the switched-mode power supplies are individuated and their mutual impedances with the victim circuit are calculated by the induced EMF method. The two-port representation of the field coupling allows the noise voltage on a victim circuit to be predicted. As a victim circuit a circular loop representing a magnetic field probe used in near field measurements is considered. The approach is applied to a flyback converter and validated through experimental measurements.

Two-Port Network Models for Compliant Rhomboidal Strain Amplifiers

Piezoelectric stack actuators have the advantages of zero backlash and no acoustic noise, but their stroke is too small to actuate robotic links directly. Because the force available is often more than the required, the stroke of the piezoelectric stack can be amplified by a compliant mechanism at the expense of force. It is not always clear what the geometry of this compliant mechanism should be. Compliant mechanisms have parallels in biology in that they describe two-way interactions between the actuator and the environment. In this paper, we employ the concept of a two-port network model from circuit theory to describe this two-way interaction and present a method to obtain each element of the two-port model as an analytical function of physical geometric parameters for a wide class of geometries. This method makes use of Castigliano's theorem and Euler-Bernoulli linearly elastic beam theory. To our knowledge, this is the first two-port representation of a compliant mechanism that is based on analytical expressions of geometric parameters. This analytical model agrees well with finite-element method calculations. We also examine a representative case experimentally and achieve accuracies better than 18%.

Two-Port Representation of an Antenna With Application to Non-Foster Matching Networks

A new theoretical tool is introduced for treating an antenna as a two-port network. This tool is very useful for allowing the antenna and its matching network to be analyzed and optimized in a circuit simulator. In this paper, we apply the idea to the situation where the matching network of the antenna incorporates non-Foster (active) matching elements, and so overall circuit stability becomes an overriding consideration. Non-Foster matching networks are particularly interesting because they offer the potential to transform the antenna into an active component that is no longer limited by the gain-bandwidth-size constraints of passive antennas, and whose performance can be improved as semiconductor technology advances.

Alternative approaches for linear analysis and prediction of a synchronous generator under partial- and full-load rejection tests

This work introduces the so-called linear hybrid state model of a synchronous machine based on the superposition principle of the two-port representation of the d-axis (two-port circuits) and the single-port structure of a q-axis equivalent circuit. The detailed formulation of the linear hybrid state model is developed in terms of the equivalent circuit parameters of the machine. As the terminal voltages and the field current recorded after full- and partial-load rejection tests are the generator's time-variant responses for a step change of armature currents with a constant field voltage, exact analytical expressions of the terminal voltages and the field current following the generator tripping (load rejection) tests are derived in terms of physical machine parameters using the state model solution of the linear system theory. Two load rejection tests (50% and 100%) of purely inductive and capacitive load are performed and comparisons are made between simulation results and actual data obtained from a four-pole, 1.5-kVA, 208-V, 60-Hz laboratory machine.

Optimization Algorithm for Fault Location in Transmission Lines Considering Current Transformers Saturation

This paper deals with fault location calculations that use voltages and currents during transient conditions and pre fault values. The method uses transmission line measurements at both terminals and its main contribution is the possibility of fault location even with the lack of some current measurements as in the case of current transformers saturation or even when data acquisition process fails. The equations are based on two-port line representation that can be applied to transposed or untransposed lines and equivalent impedances at the terminals are not needed. With the proposed formulation, the algorithm does not use simplifying assumptions to calculate the fault distance and the fault resistance simultaneously. For phase-to-ground faults, the possibility of lack of accurate current measurement in one CT is assumed. For double phase-to-ground faults and three phase faults, the lack of measurements in two or three CTs, respectively, is also assumed. The results, considering different line configurations and fault types, are presented, showing the accuracy and efficiency of the proposed method.

A New Approach for Closed-Form Transient Analysis of Multiconductor Transmission Lines

A novel closed-form model for multiconductor transmission lines is presented. The proposed model is derived from the analytical characterization of half-T ladder networks, which using closed-form polynomials (named DFF and DFFz), allow one to exactly extract poles and residues of the two-port representation of multiconductor transmission lines, thus, generating a time domain macromodel that can be incorporated in a circuit simulator. Since the model is derived from a stable and passive equivalent network, its stability and passivity are strictly preserved. Simulation results for one, two, and three-conductor transmission lines with linear and nonlinear terminations are presented, confirming the validity of the proposed model.

A New Methodology for the Transient Analysis of Lossy and Dispersive Multiconductor Transmission Lines

This paper presents a new technique for the transient analysis of multiconductor transmission lines (MTLs). The proposed model is derived from the analytical characterization of half-T ladder networks (HTLNs), which approximate the MTLs. Using closed-form polynomials (named D'Amico-Faccio-Ferri (DFF) and DFFz), poles and residues of the two-port representation of MTLs are extracted analytically, thus leading to a time-domain macromodel, which can be incorporated in a circuit simulator. Furthermore, the knowledge of poles allows one to develop an efficient model order reduction technique by selecting only the dominant poles of the system within a fixed bandwidth. Stability and passivity properties of the proposed model are intrinsically enforced as a consequence of stability and passivity of HTLNs and rational approximation procedure.

Experimental Quantitative Comparison of Different Control Architectures for Master–Slave Teleoperation

A procedure for experimental evaluation and objective/quantitative comparison among the different teleoperation architectures and systems is proposed. It is based on the analysis of the different matrices that can define the teleoperated system (two-port representations) and the selection of a set of four parameters that are easy to estimate via simple experimentation: free motion impedance, position tracking in free movement, force tracking in hard contact tasks and maximum transmittable impedance. These parameters provide complete characterization of the master-slave system and have clear physical interpretation. Furthermore, they require no maneouvering of the slave robot, which is very useful in the case of heavy or nonaccessible industrial robots. The method has been applied to compare position-position (PP), force-position (FP), and four-channel (4C) controllers in a 2 DOF master-slave system. Experimental measuring for all four parameters will be shown, proving the 4C architecture clearly better than any other.

Time-domain two-port representation of some nonuniform two-conductor transmission lines

This brief proposes a new procedure to extend to nonuniform transmission lines, a time-domain model commonly used to describe uniform transmission lines. The line is represented at its terminations as a dynamic two-port, where each port is composed by a dynamic one-port connected in series with a controlled voltage source. The procedure is applied to nonuniform lines with exponential, linear and Gaussian profile of the parameters. The numerical analysis of some case-studies is carried out.

Improvement of thermal nodal models with negative compensation capacitors

The objective of the present study is to improve the modelling of heat transfer by elementary cells, aiming to increase the quality of their representation in the Laplace space. From the twoport representation and its connections with the classical nodal method, we show that the systematic increase of the order leads to improve the simulation results in transients. But, we would like to find a better reduced topology of the equivalent elementary network of heat conduction, closer to the analytical solution and verifying its terms for higher orders. The wall representation can be performed by an impedance network with “ Π ” or “ T ” shaped cells. The approximation of these impedances leads to define a new cell topology, which introduces capacitances with a negative value called capacitors. The value of these new elements only depends on the model nodal thermal capacitances in a wall. We study the transfer functions of these various equivalent networks as twoports that we will then compare to the analytical solution of the heat transfer equation. Some interesting values of the negative compensation capacitors are then obtained from transfer function; however, the optimal value would only be given from simulation results. All the established results will be confirmed by transient response simulations, which show the high performances of these new structures. These results are also validated by a modal analysis of these systems. The study of the model's accuracy show that the importance of the reduction for equivalent maximum errors corresponds to the square of the number of elementary cells.

A unified approach to RF and microwave noise parameter modeling in bipolar transistors

A unified approach to RF and microwave noise parameter modeling in bipolar transistors is presented. Circuit level noise parameters including the minimum noise figure, the optimum generator admittance, and the noise resistance are analytically linked to the fundamental noise sources and the y-parameters of the transistor through circuit analysis of the chain noisy two-port representation. Comparisons of circuit level noise parameters from different physical models of noise sources in the transistor were made against measurements in UHV/CVD SiGe HBTs. A new model for the collector shot noise is then proposed which produces better noise parameter agreement with measured data than the SPICE noise model and the thermodynamic noise model, the two most recent Y-parameter based noise models.

Noise parameter optimization of UHV/CVD SiGe HBT's for RF and microwave applications

This paper demonstrates a predictive noise parameter estimation methodology for UHV/CVD SiGe HBT's which combines ac measurement, calibrated ac simulation and two of the latest Y-parameter-based noise models: (1) the thermodynamic noise model, and (2) the SPICE noise model. The bias current and frequency dependence of the minimum noise figure, the optimum generator admittance, and the noise resistance are calculated using both models and compared with measurements. The observed agreements and discrepancies are investigated using circuit analysis of the chain noisy two-port representation. For the devices under study, the SPICE model description of thermal noise produces a better overall agreement to data in terms of all the noise parameters. Experiments on devices with different collector doping levels show that both low noise and high breakdown voltage can be realized with one profile without significantly compromising the ac current gain and the ac power gain.

Time-domain two-port representations of a lossy line

We examine the two port representations of a lossy line in the time domain. We give a closed form expression for the canonical responses defining the adopted representation. These expressions are arranged into two contributions: an impulsive term and a regular part. The extension to the multi-conductors case described by Toeplitz, symmetric, and tridiagonal matrices is also discussed.

Heat-Transfer for Fins with Two-Port Theory

Fin heat transfer is an essential part of the education of mechanical engineers. It represents the simplest application of the heat conduction equation: the one-dimensional, steady, case. The usual presentation of the subject involves solving the conduction equation for various boundary conditions. In this paper, two-port techniques are applied to fin heat transfer. This concept is more suitable for the training of engineers because it emphasizes the importance of the boundaries rather than the internal conduction. Besides this important conceptual aid, the matrix is a powerful aid in computations; making it much easier to solve arrangements with complicated geometry. In fact, the two-port representation makes it possible to use graph theory for the automatic solution of complicated heat-flow structures.

Dual-channel and multifrequency radar system calibration

Uncertainty in absolute gain and crosstalk factors are the primary sources of error in dual-channel radar measurements. A full two-port calibration technique compensates for the errors introduced due to an imperfect antenna system and improves the isolation between orthogonal polarization channels as long as the observed cross section is above the equivalent system noise cross section. A novel technique for calibrating a dual-polarized network analyzer-based scatterometer system is discussed. Rigorous two-port S-parameter representation is used to describe absolute gain and crosstalk characteristics. Validity of the crosstalk correction is demonstrated by measuring the point target scattering matrix. Correction factors are obtained by measuring the S-parameters of trihedral and dihedral comer reflectors of known sizes. Results of absolute gain of the antenna system are verified using independent test target cross section measurements.

Feedback representation of a noisy two-port

The maximal signal-to-noise ratio and either matching to the resistive source, or maximum gain from the reactive source can be simultaneously achieved when the two-port input impedance is complex conjugate with respect to the optimal source impedance. A noisy two-port representation is derived using only two noncorrected noise sources.

Accuracy of simple difference-differential equations for blood flow in arteries

This paper presents an analysis of the numerical accuracy of the representation of an arterial segment by difference-differential equations (dde) of low order ( N). The analysis is done by comparing, in the linear autonomous case, the two-port representations of the exact solution (Womersley) and of the lumped approximation (Rideout) of the flow by N annuli of constant flows. For low N (2, 3) it is shown that the dde's overestimate greatly the longitudinal impedance of the artery. For higher N, we give a closed-form expression for this longitudinal impedance approximation and show that it converges toward the Womersley solution for N → ∞. However for N ⩽ 5 (which are the only practical cases) the error in longitudinal impedance remains large. Finally, the practical influence of these errors, is shown on a model of the pulmonary vascular bed of the dog for which the use of Rideout's method completely destroys the input impedance pattern shown by the Womersley solution.