General Circuit Model Research Articles

Generalized Model for Multiband Metamaterial Transmission Lines

In this letter, a generalized circuit model valid for the description of composite right/left handed metamaterial transmission lines with an arbitrary number of bands is presented for the first time. The model is a T- or pi-circuit where the series branch is composed of parallel connected series resonators, and the shunt branch consists on series connected parallel resonant tanks. It is demonstrated that any arbitrary T- or pi-circuit exhibiting alternate left-handed and right-handed bands can be expressed in the form of the proposed circuit. This justifies the consideration of the circuit as a generalized model of multiband metamaterial transmission lines.

Input and Output Cross-Coupled Wideband Bandpass Filter

A new wideband bandpass filter configuration with input-output cross-coupling is investigated. The new filter is based on a transmission line filter with short-circuited stubs. In order to allow the filter to exhibit high selectivity filtering characteristic and to enhance the group delay with only a few resonators, cross-coupling between the input and output feed lines is introduced. As a result, new symmetrical pairs of transmission zeros are generated at the lower and upper stopbands, leading to a quasi-elliptic function response that improves the passband and out-of-band performances. A general circuit model for the proposed filter is presented and a demonstrator with approximately 48% ripple bandwidth at a midband frequency of 3 GHz is developed. The design is successfully realized in theory and verified by full-wave electromagnetic simulation and the experiment, where excellent agreement is obtained.

EQUIVALENT CIRCUIT MODEL FOR ANALYSIS OF INHOMOGENEOUS GRATINGS

A general circuit model is proposed for frequency domain analysis of inhomogeneous two-dimensional periodic gratings. Each component of electromagnetic fields is expressed by several spatial harmonic plane waves. Then, two differential equations and two boundary conditions are obtained for the electric and magnetic vectors. Finally a circuit model is introduced for the obtained equations. The circuit model consists of loaded and excited nonuniform coupled transmission lines (CTL).

Equivalent circuit model for left-handed metamaterials

A general equivalent circuit model to calculate the effective permeability of various configurations of split-ring resonators (SRRs) is presented. In the proposed model, each column of the SRR units along the axis of the rings is modeled as a quasisolenoid under magnetic induction. The inductance per ring of the infinite column of these rings is calculated, assuming all the rings in this column support the same current. The electromagnetic coupling between these individual columns of the rings is integrated into this circuit model, which is then applied to a two dimensional cross embedded split-ring resonator. The agreement between the predicted results and numerical simulations shows the efficiency of the model in predicting the frequency band of negative permeability.

Determination of Generalized Permeability Function and Field Energy Density in Artificial Magnetics Using the Equivalent-Circuit Method

The equivalent circuit model for artificial magnetic materials based on various arrangements of split rings is generalized by taking into account losses in the substrate or matrix material. It is shown that a modification is needed to the known macroscopic permeability function in order to correctly describe these materials. Depending on the dominating loss mechanism (conductive losses in metal parts or dielectric losses in the substrate) the permeability function has different forms. The proposed circuit model and permeability function are experimentally validated. Furthermore, starting from the generalized circuit model we derive an explicit expression for the electromagnetic field energy density in artificial magnetic media. This expression is valid at low frequencies and in the vicinity of the resonance also when dispersion and losses in the material are strong. The presently obtained results for the energy density are compared with the results obtained using different methods.

A general circuit model for defected ground structures in planar transmission lines

This paper presents a general circuit model for planar transmission line defected ground structures (DGS) that exhibits multi electromagnetic band gaps or stop bands in frequency responses. The proposed equivalent circuit consists of lumped elements that can be easily extracted from full-wave EM simulations. It is simple and accurate for modeling a wide range of DGS in microstrip and coplanar waveguide over a broad bandwidth. Excellent agreement with EM simulations/measurements is demonstrated.

Photoelectrochemical oxidation behavior of organic substances on TiO2 thin-film electrodes

The photoelectrocatalytic oxidation characteristics of salicylic acid, formic acid and methanol on anodized nanoporous titanium dioxide (TiO2) thin-films were investigated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. From dark to ultraviolet illumination, the open circuit potential (OCP) and film resistance of TiO2 films decreased markedly. A general equivalent circuit model was proposed for the photoelectrochemical system anodic TiO2 thin-film electrode/test solution. The photoelectrochemical oxidation process of the organic compounds showed similar impedance features at OCP and was controlled by the charge transfer step. According to the polarization curves of the base solution and organic solutions, the kinetic rate curves for the photoelectrocatalytic oxidation of pure organic species were obtained as a function of the potential bias. One photooxidation peak was first observed at a bias potential of ca. 0.26 V for these species with low concentrations.

Continuous-time active-RC filter model for computer-aided design and optimization

A general circuit model is presented for integrator-based continuous-time active-RC filters, consisting of inverting amplifiers and a passive feedback network. The structure is analyzed using a matrix description and the explicit transfer-function formula is given for the general case. Extensions of the model are given that take into account finite dc gain and bandwidth of operational amplifiers, as well as other nonideal effects. Noise analysis of the active-RC filters is performed in a general setting. The matrix-based approach is formulated especially for the efficient use in computer-aided analysis and design of active-RC filters. As illustrations, a few application examples of the proposed approach are given.

A new method for determination of parasitic capacitances for PHEMTs

A new direct extraction method for the determination of the parasitic capacitances of PHEMTs is presented in this paper. This method is based on a general scalable small signal equivalent circuit model under pinch-off bias condition. The main advantage of this approach is that all parasitic capacitances including Cpg, Cpd and Cpgd can be extracted simultaneously by using PHEMTs of different sizes but with the same pad structure. Good agreement is obtained between modelled and measured results for 2 × 20 µm, 2 × 40 µm, 2 × 60 µm and 2 × 100 µm gate width (number of gate fingers × unit gate width) double heterojunction δ-doped PHEMTs.

Comprehensive study of noise processes in electrode electrolyte interfaces

A general circuit model is derived for the electrical noise of electrode–electrolyte systems, with emphasis on its implications for electrochemical sensors. The noise power spectral densities associated with all noise sources introduced in the model are also analytically calculated. Current and voltage fluctuations in typical electrode–electrolyte systems are demonstrated to originate from either thermal equilibrium noise created by conductors, or nonequilibrium excess noise caused by charge transfer processes produced by electrochemical interactions. The power spectral density of the thermal equilibrium noise is predicted using the fluctuation-dissipation theorem of thermodynamics, while the excess noise is assessed in view of charge transfer kinetics, along with mass transfer processes in the electrode proximity. The presented noise model not only explains previously reported noise spectral densities such as thermal noise in sensing electrodes, shot noise in electrochemical batteries, and 1/f noise in corrosive interfaces, it also provides design-oriented insight into the fabrication of low-noise micro- and nanoelectrochemical sensors.

A simple and effective process for noise reduction of multichannel cortical field potential recordings in freely moving rats

Simple and useful steps, i.e. placing a grounded plate under the recording chamber as well as using multiple reference electrodes, are introduced here for obtaining reliable low-noise recordings of brain activity in freely moving rats. A general circuit model was built to analyze the electrical interference of both single-grounded and two-reference ground-free recording configurations. In both simulated and realistic conditions under two recording states, 60-Hz magnitude was in the microvolt range. Moreover, the noise was significantly reduced by shortening the distance between the subject and the grounded plate under the recording chamber. Furthermore, in chronically implanted rats, average 60-Hz interference of multichannel electroencephalograms of two-reference ground-free recordings (3.74±0.18 μV) was significantly smaller than that of the single-grounded condition (9.03±1.98 μV). Thus, we demonstrated that a lower-noise recording can be achieved by a two-reference configuration and a closely-placed metal grounded plate in an open-field circumstance. As compared to the use of a Faraday cage, this simple procedure is of benefit for long-term behavioral tracking with a video camera and for pharmacological experiments.

A general nonlinear model of switched reluctance motor with mutual coupling and multiphase excitation

This paper presents a general nonlinear magnetic equivalent circuit model of a switched reluctance machine (SRM) that includes all possible flux paths in 2-D view of the machine, taking into account mutual coupling between phases and multiphase excitation. The model can be used to predict the performance of the machine with short or full pitched winding in static and dynamic regimes. Therefore, it is a simple analysing tool for finding the best configuration of SRM in computer-aided design and optimal design. A novel technique is employed to model the lumped elements of stator and rotor poles, and a new representation of the rotor core is introduced. Also, a general numerical matrix procedure is developed to calculate the total machine torque, and an approximate analytic alternative is presented. Inclusion of the rotor skew in the new model is described, and the accuracy of the model is verified by comparison of the simulation results with those obtained by the finite element method and measurements.

Corrosion protection of AA6061 T6 by fluoropolymer coatings in NaCl solution

The corrosion protection performance of epoxy-treated fluoropolymer-coated AA6061 T6 alloy was studied. Two types of fluoropolymer with different fluorine ratios (FLBZ 1074 and modified FLBZ 1074) were applied as top coatings. Electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion resistance of such coatings in 3.5% NaCl solution under uniform and scratched conditions. Uniform coatings showed excellent corrosion protection even after 4 months of immersion in NaCl. Conversely, the corrosion rates increased dramatically under the scratched conditions after less than 1 month of immersion in NaCl due to filiform corrosion. A general equivalent circuit model has been used to analyse the impedance data in terms of reactions occurring during the interaction of the coated specimens with the environment. Based on the results of this analysis, together with the visual inspection, FLBZ 1074 coating was found to be more efficient than the modified FLBZ 1074 coating in providing corrosion protection in NaCl.

Analysis and modeling of microstrip-to-coplanar flip chip package interconnects

In this paper, the discontinuity of a flip chip transition between a microstrip line and a coplanar waveguide is investigated and modeled using the finite-difference time-domain method (FDTD) to predict the overall S-parameters of the package. Effects of the bump and via interconnects on the package performance are investigated and discussed. This includes the effects of different staggered transitions and ground connects on the package performance. A reduction of about 10 dB in the bump and via reflections can be achieved by staggering the signal (bump) and the ground connects (bump/via). A staggering distance of about twice the slot width gave minimum reflection over a wide band of frequencies. Moreover, the larger the relative distance between the ground and the center connects the less the reflection due to the discontinuity. Finally, the computed S-parameters of the flip chip package using the FDTD solution are used to develop an equivalent circuit model for the transition discontinuity over a wide frequency band. The equivalent circuit model of the microstrip to coplanar waveguide discontinuity includes more elements and is more complex than other types of transitions. A TEE or PI circuit model has been used to approximate the general circuit model of the discontinuity. Good agreement has been obtained between the S-parameters of the FDTD model and the equivalent circuit models over a wide frequency band. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 202–211, 2001.

Magnetic circuit model for the mutually coupled switched-reluctance machine

The mutually coupled switched-reluctance motor (SRM) appears to have several performance advantages over other motor technologies. The existence of strong coupling between phases, however, makes the analysis of this machine quite complicated. Preliminary design of this machine can be greatly accelerated by the ability to evaluate potential motor geometries quickly. This paper introduces a general magnetic circuit model of the mutually coupled SRM that adapts to any geometry, unlike existing geometry-dependent approaches (such as finite elements), which are numerically intensive and require excessive computation time. The model uniquely implements the magneto-motive force (mmf) sources necessary to accommodate complex flux paths through the machine and includes the effects of magnetic saturation. The results are compared to those of a finite element solver to demonstrate the performance of this method as a first-step to evaluating candidate designs.

Two-dimensional simulation of conducted currents characteristics in electrical discharges

In this paper, a simple general electrical discharges circuit model for electrical discharge current waveform simulation in overvoltaged air gaps is presented. A macroscopic circuital method of simulation utilizing the standard SPICE network simulator, based on a two-dimensional (2-D) nonlinear impedances network has been proposed. The structure of the simulation framework is designed to take into account the electrode geometries in a straightforward way. A study of conducted current waveform for different electrode geometries has been done. Experimental data have been used to validate the simulation results.

Synthesis of hazard-free asynchronous circuits based on characteristic graph

To synthesize hazard-free asynchronous circuits from Signal Transition Graphs (STGs), we present a new Characteristic Graph (CG) to encapsulate all feasible solutions of the original STG in reduced size, which compares favorably with the state graph approach. Based on CG, we are able to explore the design space, as well as develop a necessary and sufficient condition for hazard-free realization on a predefined general circuit model, which has not yet been reported. The exact optimization for synthesis is shown to be NP hard. A heuristic method is thus proposed which results in efficient solutions while requiring very little CPU time.

Static and dynamic hysteretic features in a PWL circuit

The general properties of the static and dynamic hysteretic behaviours of a PWL ladder circuit are described and discussed. These properties are obtained on the basis of some results reported in a previous paper (M.Parodi et al., Int. j. circ. theor. appl., 22, 513 (1994), concerning the static hysteretic behaviour of the same circuit. Despite the non-linearity of the circuit, the main features of its hysteretic behaviour are shown to depend on the parameters of the circuit components in a simple way. Moreover this behaviour is similar to those observed in a large number of experiments. For these reasons, the PWL ladder circuit is taken as the central element of a general circuit model for hysteresis. The structure of this general circuit is described at the end of the paper.

An accurate equivalent circuit model of flip chip and via interconnects

In this paper, the transition discontinuities of flip chip circuits are modeled and investigated using finite-difference time-domain (FDTD) method to predict the S-parameters of different packages. This includes transition between two coplanar lines on the chip and mother board and transition between two striplines in a package. The computed S-parameter of the flip chip package using the FDTD model are used to develop an equivalent circuit for the transition discontinuity over a wide frequency band. A general and accurate equivalent circuit model of the interconnect has been developed and presented. In this circuit model, a statistical analysis is used to compute the value of the circuit elements. Also, losses in the flip chip package are represented by a simple function versus frequency. These losses include substrate loss of the chip and the mother board due to excitation of surface wave and radiation loss due to the bump. Conductor and material substrate losses are not included in this circuit model. Good agreement has been obtained between the S-parameters of the FDTD model and the equivalent circuit model over a wide frequency band of up to 50 GHz. Furthermore, the effects of the bump dimensions on the equivalent circuit model has been also evaluated and presented. The results show important issues in the design of the flip chip interconnect. The bump dimensions can be used as impedance matching parameters to achieve minimum losses over a wide frequency band. The presented equivalent circuit model can be used in commercial circuit simulators to predict monolithic microwave/millimeter wave integrated circuit (MMIC) performance including the package.

Invariance of S/sub 21//S/sub 12/ and K-factor under parallel operation of linear two-port devices

Based on a generalized circuit model for parallel-operated amplifiers with linear two-port devices, it has been proved that the S-parameter ratio S/sub 21//S/sub 12/ and hence MSG (maximum stable gain) are invariant as long as the devices have an identical value of S/sub 21//S/sub 12/ and the input and output networks are reciprocal. The invariance of K factor has been shown to hold for two cases: (i) devices are identical and input/output networks are lossless and symmetric with respect to each device, and (ii) identical admittances are added to the networks of case (i) so as to connect every device port with each other. Thus at least in these two cases, MAG (maximum available gain) and U (unilateral gain) are invariant as well as MSG under parallel operation of linear two-port devices. The invariance of S/sub 21//S/sub 12/ and hence MSG applies to a variety of parallel-operated amplifiers such as distributed amplifiers and linear power amplifiers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>