Resistor Model Research Articles

Modeling and quantitative analysis of connectivity and conductivity in random networks of nanotubes

The work describes the framework that allows performing a computer simulation of complex random networks of conducting nanotubes embedded in the dielectric medium. The representative volume element filled with a large number of interconnected nanotubes is modeled and the tunneling conduction mechanism between adjacent tubes is considered. The principal goal is to develop a computational approach for the three­dimensional multielement structure simulation, which will be relatively simple, yet capable of producing realistic results. The connectivity formation processes among nanotubes in random nanotube networks are studied using the elements of graph theory. All stages of the modeling process are discussed in details. The system conductivity model with taking into account the tunnel effect and intrinsic nanotube conductivities is formulated. The random resistor model is used to calculate the total equivalent conductivity of the network. The results of the computer experiments on electrical conductivity simulations for different systems are presented. The dependencies of the electrical conductivity of nanotube networks in the insulating medium on the concentration of nanotubes, geometric parameters and properties of tunneling conductivity between individual tubes are investigated. It is found that the percolation threshold corresponds to the nanotube loading of 0.5 % when the aspect ratio of nanotubes is 160. Non­linear dependence between the aspect ratio and the percolation threshold was established. The analysis of computational complexity and calculation time is performed for quad­core computing systems. Computer experiments carried out in a systematic fashion within the proposed framework can be useful when designing novel CNT­polymer composites for state of the art electronic applications. By following the predictions of the proposed model, tailoring of electrical properties of such composites can be made easier when adjusting the parameters of nanotubes and their concentration during the fabrication of the nanocomposite samples.

Effect of mobility ratio on interaction between the fingers in unstable growth processes.

We investigate interactions between thin fingers formed as a result of an instability of an advancing front in growth processes. We show that the fingers can both attract and repel each other, depending on their lengths and the mobility ratio between the invading and displaced phase. To understand the origin of these interactions we introduce a simple resistor model of the fingers. The predictions of the model are then compared to the numerical simulations of two unstable growth processes: dissolution of partially cemented rock fracture and viscous fingering in a regular network of channels.

Investigation on Eddy Current Sensor in Tension Measurement at a Resonant Frequency

For resolving deficiencies of conventional tension measurement methods, this paper proposes a novel eddy current sensor with a single-coil structure based on the inverse magnetostrictive effect. An inductor–resistor–capacitor (LRC) model of eddy current sensor, which considers more parameters than the traditional inductor–resistor (LR) model, was established. The eddy current sensor was operated by a swept frequency signal that ranged from 0.1 MHz to 1.6 MHz, encompassing the sensor resonant frequency. At the resonant frequency, the data of impedance magnitude and phase were extracted and linear relations between the impedance parameters and the external tension were ascertained. The experimental results show that the resonant frequency and impedance magnitude of eddy current sensor will decrease linearly with the increase of the external tension, which is consistent with the theoretical model. In addition, to improve sensor performance, the sleeve structure was designed to reduce the loss of magnetic field. Both finite element simulations and experimental results demonstrate that the sleeve structure provides a higher permeability path to the magnetic field lines than the non-sleeve structure and effectively improves sensor sensitivity and correlation coefficient.

Compact modeling approach for microchannel cooling and its validation

This paper presents a new compact modeling technique to describe the convective heat transfer realized by laminar flow of coolant in integrated microchannels used for thermal management of 3D ICs—with the aim of being able to implement this model for fast thermal simulators used in logi-thermal simulation frameworks. This model works only on laminar flow in straight channels. The compact model represents the convective heat transfer with a special resistor network representing one directional heat transfer realized by the flow of the coolant. The implementation of this model in a thermal field solver based on the successive node reduction (SUNRED) algorithm is also presented. The validation of the model is based on two examples. First, we compare the result obtained with the new model with the results provided by a commercially available CFD software for a simplified test case. The other pivot of the validation is an actual measurement of the thermal resistances of microfluidic cooling system under different flow-rates of coolant. The errors were calculated as the difference of the results of the direct implementation of the alternating resistors model, the modified SUNRED model and the result of a detailed CFD simulation for the test case. The error of the simulation of the cooling device is based on the difference of the directly measured and simulated thermal resistances. The comparison showed that the error of our new compact model was close to 5%.

A generic solar-thermochemical reactor model with internal heat diffusion for counter-flow solid heat exchange

For nonstoichiometric redox reactions that produce CO and H2 from CO2 and H2O, heat recuperation from the solid phase is a promising mechanism to improve the cycle efficiency. Many different approaches to heat recuperation and gas separation have been presented in solar thermochemical reactor concepts recently. To describe the many possible degrees of freedom in the reactor design, a generic reactor model is described for two-step redox reactions of solid pieces of reactant moving in counter flow between reduction and oxidation chambers. The reactive material is assumed to be porous ceria, where heat recuperation from the solid phase is achieved through radiation heat exchange between reduced and oxidized elements moving in opposite directions. A separation wall prevents gas cross-over and provides structural support. Heat transfer by radiation in the porous material is modeled with the Rosseland diffusion approximation and by conduction with the three resistor model. The model can be adapted to a wide range of reactor concepts.A study of crucial design parameters shows that heat diffusion in the reactive material can have a significant influence on the performance of the heat exchanger. If the time required for heat diffusion is large with respect to the total residence time in the heat exchanger, the material thickness can be decreased to enhance the share of the material actively participating in the heat exchange process. Furthermore, at the relevant temperatures, radiation dominates the heat exchange within the porous structure, thus the overall heat exchange can be enhanced through an increase of porosity. Heat exchanger length and residence time are correlated, allowing different combinations of these two variables at constant heat exchanger efficiency. In general, efficiencies close to 70% are possible with an adequate parameter combination. However, the achievement of the maximum heat exchanger efficiency requires a minimum number of chambers and thus physical length, as irreversibilities are reduced for a larger number of intermediate temperature levels.The presented generic model includes the description of heat diffusion within the reactive material, is a valuable tool for the design of heat exchangers, and can be used to identify technically interesting reactor concepts for the achievement of high energy conversion efficiencies.

Low voltage bipolar resistive switching in self-assembled PVDF nanodot network in capacitor like structures on Au/Cr/Si with Hg as a top electrode

In this letter, resistive switching phenomena in self-assembled nanodot network of Polyvinylidene fluoride (PVDF) polymer in a capacitor geometry of Hg/PVDF/Au/Cr/Si is investigated. A stable & bipolar resistive switching with a set voltage ranging from 0.35 V to 0.9 V & reset voltage with a range of −0.08 V to −0.25 V is detected. A practical resistance ratio between HRS and LRS of 10–25 may have great potential in organic memories. Possible mechanism for the bipolar switching is discussed with the filament type conduction mechanism. Furthermore, the low voltage switching is elucidated with the high current density associated filament formation and it is explicated using the parallel resistor model.

Refined model of low-impedance film resistors with a comb-like structure

Using the methods of finite element and conformal mapping, analytical models with low and ultralow resistance of the film resistors of the main types of comb-like (interdigital) structures with an arbitrary ratio between the surface resistivities of resistive and conductive films have been worked out. In the resultant resistance, the resistances of comb-like and connecting electrodes are taken into account, as well as the additional resistance caused by the passage of the current from the conductive to the resistive film and vice versa. The conditions under which an interface between the films can be treated as an equipotential surface are revealed. An equivalent circuit of low-impedance comb resistors, which are used as the sensors of the current in the circuits of stabilization and control, as well as thermal and current protection.

Innovative approach for electrical characterisation of pseudo‐resistors

Since the use of pseudo-resistors became popular in of bio-amplifiers research, several works have been published, but a lack of knowledge about accurate experimental characterisation and simulation of these non-linear devices remains. An innovative experimental procedure concerning the characterisation of pseudo-resistors is presented. The proposed experimental procedure proves the existence of a linear operation region, where the device can operate like a very high resistance, which is mainly applied on bio-amplifier designs. The main experimental results of the electrical characterisation of pseudo-resistors are described in detail and compared with the SPICE results. The pseudo-resistor experimental curve response including the non-linear operation region is presented. Finally, a new non-linear polynomial resistor model to use in SPICE simulator, replacing with success the electrical representation model based on transistors models is proposed. The presented simulations were performed with Mentor Graphics EldoTM SPICE simulator, using BSIM3V3.1 and PSP103.1 models. The MOSIS Educational Program fabricated the samples used in this work.

Transient Simulation of Mold Heat Transfer and Solidification Phenomena of Continuous Casting of Steel

A comprehensive model of heat transfer and solidification phenomena has been developed including microstructure evolution and fluctuation macrosegregation in continuously cast steel slabs with an objective of evaluation of various mold cooling conditions. The study contains plant trials, metallographic examinations, and formulation of mathematical modeling. The plant trials involved sample collection from three slab casters in use at two different steel plants. The metallographic study combined measurements of dendrite arm spacings and macrosegregation analysis of collected samples. A one-dimensional mathematical model has been developed to characterize the thermal, solidification phases, microstructure evolution, interdendritic strain, and therefore, the macrosegregation distributions. Two cooling approaches were proposed in this study to evaluate the Newtonian heat transfer coefficient in various mold regions. The first approach is a direct estimation approach (DEA), whereas the second one is a coupled approach of the interfacial resistor model and direct estimation approach (CIR/DEA). The model predictions and standard analytical models as well as the previous measurements were compared to verify and to calibrate the model where good agreements were obtained. The comparison between the model predictions and the measurements of dendrite arm spacings and fluctuated carbon concentration profiles were performed to determine the model accuracy level with different cooling approaches. Good agreements were obtained by different accuracy levels with different cooling approaches. The model predictions of thermal parameters and isotherms were analyzed and discussed.

Comprehensive behavioral model of dual-gate high voltage JFET and pinch resistor

Many analog technologies operate in large voltage range and therefore include at least one or more high voltage devices built from low doped layers. Such devices exhibit effects not covered by standard compact models, namely pinching (depletion) effects, in high voltage FETs often called quasisaturation. For example, the conventional compact JFET model is insufficient and oversimplified. Its scalability is controlled by the area factor, which only multiplies currents and capacitances but does not take into account existing 3-D effects. Also the optional second independent gate is missing. Therefore, the customized four terminal (4T) model written in Verilog-A (FitzPatrick and Miller, 2007; Sagdeo, 2007) was developed. It converges very well, its simulation speed is comparable with conventional compact models, and contains all required phenomena, including parasitic effects as, for example, impact ionization. This model has universal usage for many types of devices in various high voltage technologies such as stand-alone voltage dependent resistor, pinch resistor, drift area of power FET, part of special high side or start-up devices, and dual-gate JFET.

Intrinsic Photoconductive Switches Based on Semi-Insulator 4H-SiC

A high-purity semi-insulator 4H-SiC intrinsic photoconductive switch is presented. The photoconductive semiconductor switch device is fabricated as lateral structures with the electric contact on the same side. The effect of the SiO2 passivation layer has been investigated on the breakdown voltage. The minimum ON-state resistance is 16 $\Omega $ , and the breakdown voltage is 11 kV. A new phenomenon that two steps exist on the rising edge of the photocurrent is observed, and a model of resistor and capacitor in parallel is built to explain it.

High accuracy computational methods for behavioral modeling of thick-film resistors at cryogenic temperatures

Abstract The aim of this work was to elaborate two-dimensional behavioral modeling method of thick-film resistors working in low-temperature conditions. The investigated resistors (made from 5 various resistive inks: 10 resistor coupons, each with 36 resistors with various dimensions), were measured automatically in a cryostat system. The low temperature was achieved in a nitrogen-helium continuous-flow cryostat. For nitrogen used as a freezing liquid the minimal temperature possible to achieve was equal to −195.85 °C (77.3 K). Mathematical model in the form of a multiplication of two polynomials was elaborated based on the above mentioned measurements. The first polynomial approximated temperature behavior of the normalized resistance, while the second one described the dependence of resistance on planar resistors dimensions. Special computational procedures for multidimensional approximation purpose were elaborated. It was shown that proper approximation polynomials and sufficiently exact methods of calculations ensure acceptable modeling errors.

Modelling evaluation of Garofalo-Arrhenius creep relation for lead-free solder joints in surface mount electronic component assemblies

The use of different sets of values of creep parameter in Garofalo-Arrhenius constitutive creep relation has generated distinct magnitude of creep strain (ɛacc) and strain energy density (ωacc) for the same set of solder joints in electronic assemblies. This study evaluates the effect of the use of four set of values on predicted magnitude of damage (ɛacc, ωacc) and number of cycle to failure (Nf(εacc) and Nf(ωacc)) of two different solder joint geometries. The four set of values, proposed by Lau (2003), Pang et al. (2004), Schubert et al. (2003) and Zhang et al. (2003), are used to generate four hyperbolic sine creep relations. The relations are inputted in Ansys FEM software used to simulate the damage on Sn[3.0–4.0%]Ag[0.5–1.0%]Cu solder joints in flip chip model FC48 D6.3C457DC and resistor model R102. The components are assembled on printed circuit boards; and the relations are characterised by comparing the magnitude of each model simulation output with a reference least value. The assemblies are subjected to accelerated high-temperature cycles utilising IEC standard 60749–25 in parts. It was found that each model produces distinctive magnitude and history of stress, strain, hysteresis loop, ɛacc, ωacc, Nf(εacc) and Nf(ωacc) with the values of stress and hysteresis loop histories generated using Pang et al. and Schubert et al. models being very close. Characterisation results show that the use of ωacc as input parameter in fatigue life model proposed by Syed 2004 demonstrates higher probability of predicting accurately the damage in resistor solder joints while the use of ɛacc demonstrates higher probability for BGA flip chip solder joints. Based on these results, the authors propose a paradigm for selecting suitable constitutive model(s) for accurate ɛacc, ωacc and Nf prediction whilst suggesting the development of new solder constitutive relations.

Upper critical field, pressure-dependent superconductivity and electronic anisotropy of Sm4Fe2As2Te1−xO4−yFy

We present a detailed study of the electrical transport properties of a recently discovered iron-based superconductor: Sm4Fe2As2Te0.72O2.8F1.2. We followed the temperature dependence of the upper critical field by resistivity measurement of single crystals in magnetic fields up to 16 T, oriented along the two main crystallographic directions. This material exhibits a zero-temperature upper critical field of 90 T and 65 T parallel and perpendicular to the Fe2As2 planes, respectively. An unprecedented superconducting magnetic anisotropy is observed near Tc, and it decreases at lower temperatures as expected in multiband superconductors. Direct measurement of the electronic anisotropy was performed on microfabricated samples, showing a value of that rises up to 19 near Tc. Finally, we have studied the pressure and temperature dependence of the in-plane resistivity. The critical temperature decreases linearly upon application of hydrostatic pressure (up to 2 GPa) similarly to overdoped cuprate superconductors. The resistivity shows saturation at high temperatures, suggesting that the material approaches the Mott–Ioffe–Regel limit for metallic conduction. Indeed, we have successfully modelled the resistivity in the normal state with a parallel resistor model that is widely accepted for this state. All the measured quantities suggest strong pressure dependence of the density of states.

Effect of Tunnel Junctions and Coulomb Blockade on Semiconducting Property of Networks of Single-Wall Carbon Nanotubes

The optical and electrical characterization techniques were employed to demonstrate both experimentally and theoretically (parallel nonlinear resistor model) that the existence of tunnel junctions between semiconducting single-wall carbon nanotubes implies that the Coulomb blockade effect dominates their semiconducting property. Multiwall carbon nanotubes were added to a network of single-wall carbon nanotubes, and Raman spectroscopy and UV–vis–NIR spectroscopy enabled us to observe the semiconducting property of individual single-wall carbon nanotubes in a network with a high concentration of multiwall carbon nanotubes. However, the field effect measurement at 300 K on the network of single-wall carbon nanotubes and the electrical tunnel current measurements over a wide temperature range (4–300 K) at different bias voltages (0.001–10 V) on all of the networks revealed that the networks can be treated as networks of disordered metallic nanoparticles and the semiconducting property of single-wall carbon nanotubes is significantly diminished. Furthermore, we demonstrate that the electron tunneling in networks of carbon nanotubes cannot be fully described by models such as Efros–Shklovskii, Mott variable range hopping, electron cotunneling, or fluctuation-induced tunneling because of the diameter and length distributions in the networks. The effect of tunnel junctions on the performance of such networks for sensing applications and field effect transistors is discussed.

An Advection-Diffusion Model for the Vacancy Migration Memristor

This paper proposes the advection-diffusion equation for modeling the bipolar memristor. The model identifies limiters to switching speed, reproduces general experimental results including those relating temperature dependence of $I$ – $V$ curves, and abstracts the contemporary dual variable resistor model. The model also reveals implicit complex resistors that cause the fleeting negative resistance characteristic in the memristor, as observed by Chua. Elegant closed-form solutions with remarkable scope are produced even under simplified modeling conditions. Numerical methods verify the closed form model. The proposed model uniquely derives all memristive behavior from a single governing advection-diffusion equation and bridges the vacancy and circuit domain abstractions.

The research of new fibre-optic current sensor based on thin-film resistor

As the improving of the grade of voltage and current in the power transmission lines, the traditional method that based on the electromagnetism principle already could not satisfy the need of practice. Therefore, a measurement system of passive optical fibre DC current sensor based on thin-film resistor is designed in this article. A three-dimensional model of a thin-film resistor established by ANSYS gets on simulation analysis to build a complete test system. In the low-pressure side, the appropriate algorithm can be selected for processing data. Experimental results indicate that the general linear correlation between the time constant of fluorescent lifetime and the voltage across the thin-film resistor.

Hybrid Resolution of Solar Cells Model Parameters Using Analytical and Numerical Method

This paper presents a simple and accurate method for modeling photovoltaic solar cells panels. The model adopted is single-diode/two resistors, and then, five parameters must be identified. The method uses just the normal data provided by the manufacturer to calculate the model parameters. It based on numerically method to solve one equation expressed as a function of series resistor model, while the other parameters (depending exclusively on the series resistance model) are determined analytically. The accuracy of the resulting model is confirmed experimentally for two modules from different manufacturers and distinct technologies.

Thermal conductivity correlations of open-cell foams: Extension of Hashin–Shtrikman model and introduction of effective solid phase tortuosity

Open-cell foams have emerged as promising materials for use in heat sink and heat exchanger applications. The thermal behavior of open-cell foams depends on their microscopic structure. The effective thermal conductivity of open-cell porous foams can be measured using experimental techniques, predicted from the 3-D direct numerical simulations on reconstructed foam structures obtained from micro-computed tomography images or derived from idealized structure thermal analysis. Based on the tetrakaidecahedron unit cell and different strut morphologies, three dependent and interdependent empirical correlations for effective thermal conductivity were derived. They encompass all morphological parameters and ratios of constituent phases of foams of different materials.In this process, the Hashin–Shtrikman (HS) bounds model was first extended and applied to the resistor model. A correlation term, Ω was introduced to take into account the thermal conductivities of constituent phases and the morphological parameters of the foam structure. Secondly, a more complex effective model that is a combination of series and parallel models was derived by introducing effective solid phase tortuosity. Lastly, a simple model (KT-model) was derived that can be used to predict either effective thermal conductivity or intrinsic solid phase conductivity depending upon which one of these quantities is known. The present study clearly demonstrates that the proposed empirical correlations yield extremely accurate estimates of the effective thermal conductivity for all the experimental and numerical data of different foam materials reported in the literature.

Contact transfer length investigation of a 2D nanoparticle network by scanning probe microscopy

Nanoparticle network devices find growing application in sensing and electronics. One recurring challenge in the design and fabrication of this class of devices is ensuring a stable interface via robust yet unobstructive electrodes. A figure of merit which dictates the minimum electrode overlap required for optimal charge injection into the network is the contact transfer length. However, we find that traditional contact characterization using the transmission line model, an indirect method which requires extrapolation, is insufficient for network devices. Instead, we apply Kelvin probe force microscopy to characterize the contact resistance by imaging the surface potential with nanometer resolution. We then use scanning probe lithography to directly investigate the contact transfer length. We have determined the transfer length in graphene contacted devices to be 200–400 nm, thus apt for further device reduction which is often necessary for on-site sensing applications. Simulations from a two-dimensional resistor model support our observations and are expected to be an important tool for further optimizing the design of nanoparticle-based devices.