A simple equivalent circuit for interdigital transducers based on the coupled-mode approach

The coupled-mode approach is a powerful tool for analyzing surface acoustic wave (SAW) periodic structures such as reflectors and interdigital transducers. The relations among the terminal quantities at two acoustical ports and one electrical port of an interdigital transducer (IDT) are derived from coupled-mode equations. A simple distributed-parameter equivalent circuit representing the entire IDT is proposed. A few examples of applications of this equivalent circuit to analysis of SAW devices are presented.     

Empirically-derived capacitor characteristic formulas from distributed modelling

Diffusion equation modelling is used to develop formulas for the normally fixed values of capacitance and resistance of the traditional capacitor equivalent circuit. The formulas define the dependence of the equivalent circuit values on metal film resistivity, capacitance per unit area, areal dimensions of the metallisation and on frequency. A multilayer capacitor topology, having both capacitor plates connected at the same end, is used for the derivation, but it is shown that the results are also representative for the more standard double-end connected topologies with some restrictions above the typical self-resonance frequency of these capacitors. The formulas allow accurate prediction of dissipation factor and input impedance according to the design parameters used in constructing the capacitor, thus providing powerful tools in capacitor design. The algorithms also facilitate the determination of internal voltages, currents and power distribution within the capacitor, thus exposing the effects, for example, of partial edge disconnection. The formulas may potentially provide a better capacitor equivalent circuit with dependent variables for circuit emulation. In the paper, the derivation process is described and the formulas tested against experimental results. A simple addition to the equivalent circuit is also included to model dielectric loss which dominantly determines the dissipation factor at low frequency     

Method for predicting f/sub T/ for carbon nanotube FETs

A method based on a generic small-signal equivalent circuit for field-effect transistors is proposed for predicting the unity-current-gain frequency f/sub T/ for carbon-nanotube devices. The key to the useful implementation of the method is the rigorous estimation of the values for the components of the equivalent circuit. This is achieved by numerical differentiation of the charges and currents resulting from self-consistent solutions to the equations of Schrodinger and Poisson. Sample results are presented, which show that f/sub T/ can have a very unusual dependence on the gate-source bias voltage. This behavior is due mainly to the voltage dependence of the transconductance and capacitance in the presence of quasi-bound states in the nanotube.     

Analysis of Nonlinearities in Superconducting Microstrip Straight Bends; FDTD Method in Comparison with Nonlinear Circuit Modeling

This paper presents the prediction of nonlinearities in the superconducting microstrip straight bends in microwave frequencies based on two different methods; FDTD simulation as a numerical approach, and nonlinear circuit modeling as an analytical method. In the FDTD method, the superconducting microstrip structures are simulated with London’s equations. In the simulation, the penetration depth and normal conducting coefficient are considered as functions of current density of superconductor. To simulate the thin strip of superconductor, a non-uniform mesh has been used. For the nonlinear circuit modeling, we use distributed RLGC parameters for superconducting microstrip transmission lines. These parameters are considered as functions of the current distribution. This yields an equivalent nonlinear circuit model for bends. The final equivalent nonlinear circuit is analyzed using the harmonic balance (HB) method. Different straight bend structures have been considered and the two methods’ results are compared.     

An electrical circuit theoretical method for time‐ and frequency‐ domain solutions of the structural mechanics problems

Shrinking device dimensions in integrated circuit technology made integrated circuits with millions of components a reality. As a result of this advance, electrical circuit simulators that can handle very large number of components have emerged. These programs use new circuit simulation techniques and can find solutions accurately and quickly. In this paper, we apply these techniques to structural mechanics problems by adopting electrical circuit equivalents. We first apply finite element formulation to the mechanical problem. The obtained sets of equations are treated as if they are sets of equations of an equivalent electrical circuit which consists of linear circuit elements such as capacitors, inductors and controlled sources. The equivalent circuit is obtained in the form of a circuit netlist and solved using a general purpose electrical circuit simulator. Several examples showing the advantages of the circuit simulation techniques are demonstrated. Asymptotic waveform evaluation technique which is widely used for simulation of large electrical circuits is also studied for the same examples and the speed‐up advantage is shown. Copyright © 1999 John Wiley & Sons, Ltd.     

Matrix Analysis of 2-D Eddy-Current Magnetic Fields

We present an accurate equivalent circuit model to represent a 2-D eddy-current magnetic field. The magnetic field can be coupled with stranded windings and solid conductors. For use in developing formulations of impedance computation, we present two systematic matrix analysis methods based on the system equations, one using the loop method and the other using the nodal method. In the model, each solid conductor is represented by circuit branches. With this approach, the effect of eddy currents can be fully included. We also present the formulations for the computation of the total power loss for magnetic field-circuit coupled problems. We discuss a common mistake in many applications.      

Q-factor measurements of open resonators in the millimeter-waverange including coupling losses

The unloaded quality factor as well as the coupling coefficient of open resonators are determined by evaluating measured complex reflection coefficients. The cavity is described by an equivalent circuit, the parameters of this circuit are calculated by means of a least-square fit of the simulated to the measured reflection coefficients. The solution is obtained using the Householder-algorithm, which promises very fast and stable computation. This approach is capable of evaluating quality-factor measurements for each type of resonator, even with losses in the coupling aperture. Its validity is illustrated by measurements in the cm- and mm-wave range     

An improved levelized incomplete Lu method and its application to 2d semiconductor device simulation

Abstract

Numerical simulation of semiconductor devices plays a very important role in the design and development of integrated circuits. We will present a new circuit simulator with an improved Levelized Incomplete LU method to perform such simulations. To have an environment for evaluating the interaction between a semiconductor device and a circuit, we use the equivalent circuit approach. This approach allows for simple representation carrier transport models of devices through equivalent circuit elements such as voltage controlled current sources and capacitors. Therefore, we can perform mixed‐level simulation in general circuit simulators. We will take a PN diode switching circuit and MOSFET as examples to test our equivalent circuit model and the improved circuit simulator. The comparison between improved matrix solution method and the conventional method will be demonstrated too. We will also show our method yields better matrix solutions than conventional methods     

A ferroelectric capacitor macromodel and parameterization algorithmfor SPICE simulation

A compact equivalent circuit model, or macromodel, is presented which reproduces both the DC charge storage and transient switching current responses of a ferroelectric capacitor. The macromodel circuit element values are rigorously linked to physical quantities which are readily characterized with simple electrical measurements. A software package is described which both parameterizes and optimizes the model to measured data and outputs a SPICE input file. Together, the macromodel and parameterization software form a complete linkage between material characterization and circuit design which is largely transparent to the design engineer. Optimization results lend insight into the underlying theory of ferroelectric switching and the sources of nonideal charge storage. SPICE simulations demonstrate the utility of the macromodel for VLSI circuit simulation     

Determining the equivalent circuit parameters of canned solid-rotor induction motors

For designing canned solid-rotor induction motors, the conventional induction motor circuit is inadequate. Here we present an alternative equivalent circuit, one that reflects the eddy currents in all regions (cans and rotor body). The proposed model operates on a per-phase basis at a single frequency. We confirm the validity of the new equivalent circuit with numerical and analytical solutions. This analysis has shown that the classical equivalent circuit for conventional induction motors is not sufficient to obtain the circuit parameters for the canned solid rotor induction motors. We also consider certain assumptions that make the analytical approach simpler.     

An analytical investigation on the efficiency of a magnetic frequency tripler with series-connected reactors

A numerical analysis of a magnetic frequency tripler with series-connected reactors and the maximum efficiency under the optimum setting of core dimensions is described. The steady-state values of voltage, current, power, efficiency, and power factor are calculated by using the numerical method where the φ-i characteristics of saturable reactor are approximated by a fifth-order polynomial as a function of core dimensions. The core loss, iron loss, and leakage inductance are included in the equivalent circuit for the numerical analysis. The maximum efficiency is obtained by maximizing the performance index which is derived from numerical results for various values of number of turns, air gap length, and core area as parameters. It is analytically shown that the basic tripler circuit without a LC filter achieves such high efficiency as 90 percent and over. The maximum efficiency of the tripler circuit with the LC filter is about 80 percent.     

An efficient dynamic modeling method for Reissner–Mindlin plates: a Projection Equation approach

The Projection Equation has proved itself to be an excellent approach to deriving the equations of motion for elastic multi-body mechanical systems. We use this method to obtain a dynamic model for Reissner–Mindlin plates. Unlike classical modeling methods, which use Hamilton’s principle to derive the equations of motion, the Projection Equation offers a much more general and more easily handled methodology. Given a short introduction to this approach, deriving the dynamic model of the plate is straightforward, and elimination of the shear effects, which leads to Kirchhoff’s classical plate theory, is easy. Our results are equivalent to other dynamic equations described in the literature.     

Tensor representations and solutions of constitutive equations for viscoelastic fluids

An approach is developed using tensor representations to assess and characterize both the transient behavior and equilibrium states of viscoelastic fluid constitutive equations in viscometric flows. The methodology is based on the replacement of the differential constitutive equation for the deviatoric part of the viscoelastic stress tensor by an equivalent and more tractable set of differential equations for the characteristic scalar invariants. In the case of planar flows, this equivalence leads to an explicit, closed-form analytic solution for the time evolution of the extra-stress tensor that is formally expressed as a second-order fluid relation, with time-dependent coefficients. As a validation of the approach, an analysis of the transient and equilibrium system characteristics of fluid flows described by the corotational Jeffreys model and general Oldroyd-type constitutive equations is presented.     

Modeling and analysis of circular flexural-vibration-mode piezoelectric transformer

We propose a circular flexural-vibration-mode piezoelectric transformer and perform a theoretical analysis of the transformer. An equivalent circuit is derived from the equations of piezoelectricity and the Hamilton's principle. With this equivalent circuit, the voltage gain ratio, input impedance, and the efficiency of the circular flexural-vibration-mode piezoelectric transformer can be determined. The basic behavior of the transformer is shown by numerical results.     

A new approach to solving stochastic programming problems with recourse

A new numerical approach to the solution of two-stage stochastic linear programming problems is described and evaluated. The approach avoids the solution of the first-stage problem and uses the underlying deterministic problem to generate a sequence of values of the first-stage variables which lead to successive improvements of the objective function towards the optimal policy. The model is evaluated using an example in which randomness is described by two correlated factors. The dynamics of these factors are described by stochastic processes simulated using lattice techniques. In this way, discrete distributions of the random parameters are assembled. The solutions obtained with the new iterative procedure are compared with solutions obtained with a deterministic equivalent linear programming problem. It is concluded that they are almost identical. However, the computational effort required for the new approach is negligible compared with that needed for the deterministic equivalent problem.     

Derivation of an electronic equivalent of QHE devices

Models of quantum Hall effect (QHE) devices described by an equivalent circuit are used both to analyze measurement systems and to study QHE physics. Although the most widely used equivalent is the one proposed by Ricketts and Kemeny, various other circuits have been published to suit to different needs in QHE analysis, including a network with only resistors and unity-gain amplifiers. In the following we discuss a general approach to the analysis of the electrical behavior of QHE devices, and show that they can be classified as gyrators. Gyrators are nonreciprocal network elements whose properties are well known from the theory of electrical network. They can be regarded as generalized equivalents of Hall effect devices, thus setting a general framework for the study of the electrical behavior of QHE and the derivation of equivalent circuits. Through the application of this technique, an electronic circuit capable of simulating a QHE device with nonnull longitudinal resistance is derived     

Modified nodal analysis: an essential addition to electricalcircuit theory and analysis

The known limitations of classical mesh and nodal methods of analysing linear electrical circuits are described before considering an established modification of the nodal approach. The method, known as 'modified nodal analysis', has none of the limitations of the basic nodal technique and is well suited both to symbolic and numeric analysis of complex circuits using modern matrix-based software. The simplicity of incorporating into the matrix equations all types of passive and active circuit elements is demonstrated and examples are used to illustrate further the efficacy of the method. It is emphasised that the absence of this circuit analysis technique from many academic engineering courses is totally at variance with its widespread application in modern circuit simulation packages     

Electrical and mechanical fully coupled theory and experimental verification of Rosen-type piezoelectric transformers

A piezoelectric transformer is a power transfer device that converts its input and output voltage as well as current by effectively using electrical and mechanical coupling effects of piezoelectric materials. Equivalent-circuit models, which are traditionally used to analyze piezoelectric transformers, merge each mechanical resonance effect into a series of ordinary differential equations. Because of using ordinary differential equations, equivalent circuit models are insufficient to reflect the mechanical behavior of piezoelectric plates. Electromechanically, fully coupled governing equations of Rosen-type piezoelectric transformers, which are partial differential equations in nature, can be derived to address the deficiencies of the equivalent circuit models. It can be shown that the modal actuator concept can be adopted to optimize the electromechanical coupling effect of the driving section once the added spatial domain design parameters are taken into account, which are three-dimensional spatial dependencies of electromechanical properties. The maximum power transfer condition for a Rosen-type piezoelectric transformer is detailed. Experimental results, which lead us to a series of new design rules, also are presented to prove the validity and effectiveness of the theoretical predictions.     

New equivalent lumped electrical circuit for piezoelectric transformers

A new equivalent circuit is proposed for a contour-vibration-mode piezoelectric transformer (PT). It is shown that the usual lumped equivalent circuit derived from the conventional Mason approach is not accurate. The proposed circuit, built on experimental measurements, makes an explicit difference between the elastic energies stored respectively on the primary and secondary parts. The experimental and theoretical resonance frequencies with the secondary in open or short circuit are in good agreement as well as the output "voltage-current" characteristic and the optimum efficiency working point. This circuit can be extended to various PT configurations and appears to be a useful tool for modeling electronic devices that integrate piezoelectric transformers.     

An SCR frequency tripler

The circuit and the operation of an SCR frequency tripler are described. The modes of operation are discussed and the circuit behavior is analyzed for different output conditions. An approximate equivalent circuit is used to describe the load conditions. Experimental results are shown for the open-circuited, short-circuited, and loaded frequency tripler.