Simple Equivalent Electrical Circuit Research Articles

Non-Invasive Measurement of Impedance Spectra Distribution in Polymer Electrolyte Fuel Cells

Localized measurement of the impedance distribution in an operating polymer electrolyte fuel cell stack is of great importance in providing information on its state of health and performance. However, the current methods’ invasiveness is a brake to a more widespread utilization. This work presents a non-invasive way to measure and interpret local impedance spectra. It is based on local AC current supply and local voltage measurements performed all around the cell via conductive pins contacting the outer surface of the flow fields. The different local spectra are measured on a single cell within a 200 cm2 six-cell stack under different operation conditions and compared to a reference case with homogeneous current density. A simple equivalent electrical circuit is used to fit the impedance spectra and to extract membrane and charge transfer resistance. The variations of these two values are analyzed at five different positions along the channel for different cathode stoichiometries and gas flow configurations.

Physical Interpretation of Mixed Ionic‐electronic Conductive Polymer‐coated Electrodes by a Simple Universal Impedance Model

AbstractA simple equivalent electrical circuit is used to obtain the physical parameters of electrical circuit elements from measured electrochemical impedance spectra. This model consists of four circuit elements with a clear physical meaning for each of the elements. Compared to complex models with multiple constant phase elements or Warburg impedances, our model is suitable for extracting physical values for important electrode parameters with low errors. The feasibility of the model was shown by investigating pure metal or polymer‐coated electrodes. Here, gold electrodes were coated either with Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT : PSS), Polypyrrole:poly(styrenesulfonate) (PPy : PSS), or (PEDOT/PPy) : PSS by means of electropolymerization. The model could demonstrate the ionic‐electronic differences such as the ion accessibility of the differently coated electrodes. To prove the correctness of the model, the obtained results were compared to the literature.

Impedance Analysis and Noise Measurements on Multi Walled Carbon Nanotube Networks.

The electrical impedance characteristics of multi-walled carbon nanotube (MWCNTs) networks were studied as a function of CNT concentrations in the frequency range of 1 kHz–1 MHz. The novelty of this study is that the MWCNTs were not embedded in any polymer matrix and so the response of the device to electrical measurements are attributed to the CNTs in the network without any contribution from a polymer host matrix. Devices with low MWCNT packing density (0.31–0.85 µg/cm2) exhibit a frequency independent plateau in the low-frequency regime. At higher frequencies, the AC conductivity of these devices increases following a power law, characteristic of the universal dynamic response (UDR) phenomenon. On the other hand, devices with high MWCNT concentrations (>1.0 µg/cm2) exhibit frequency independent conductivity over the entire frequency range (up to 1 MHz), indicating that conduction in these devices is due to direct contact between the CNTs in the network. A simple single-relaxation time electrical equivalent circuit with an effective resistance and capacitance is used to describe the device performance. The electrical noise measurements on devices with different MWCNT packing densities exhibit bias-dependent low-frequency 1/f noise, attributed to resistance fluctuations.

An Impedance Measurement Technique for Composite Materials Moisture Level Detection Devoted to Health Monitoring in Aeronautics

The current design practice of composite material aeronautical structures imposes the use of knock-down structural material allowables to take into account the high sensitivity to environmental exposure (i.e., moisture, temperature, damages). The “moisture derating factor” comes from specific mechanical test campaign and drastically reduces the advantage of using such materials; but the continuous monitoring of the moisture content of the structure could enable the use of higher design allowables. In the framework of FUSIMCO (Work developed within the frame of the Project FUSIMCO-FUSoliera Ibrida Metallo COmposito-co-financed by MIUR-Italian Ministry of Research with DAC-Campania Aerospace District as beneficiary and Leonardo Company-Aerostructure Division as “prime” partner) project, the aim of this study is to verify the effectiveness of the impedance measurement method as a health-monitoring tool to evaluate the moisture quantity absorbed by an aeronautical composite structure. The method is based on the idea that a composite laminate can be associated with an equivalent electric circuit (EEC). Some electrical characteristics of this EEC can be associated to the moisture content of the laminate. A simple EEC model, mainly capacitive, was used. A frequency sweep was the electric stimulus signal of some electrodes, glued onto the specimens to investigate the EEC parameters variation with respect to the induced moisture content variation (gravimetrically determined). The study confirmed the possibility of effectively using the impedance measurement method as a health-monitoring tool for moisture content evaluation of a composite laminate.

Electrical impedance spectroscopy of multiwall carbon nanotube–PDMS composites under compression

Composites made of elastomers and carbon nanotubes are promising components of soft electronics due to their enhanced permittivity, conductivity and piezoresistive characteristics. It is well established that the conductivity increases dramatically near the percolation threshold, where the nanotubes are more densely packed and electron tunneling between them can occur. However, less is known about the changes in electrical characteristics of the nanotube network when the composites are compressed. Does the electrical network change in any way upon compression? Here, electrical impedance spectroscopy is used to characterize composites made of polydimethylsiloxane and multiwalled carbon nanotubes in order to determine potential changes in the electrical nanotube network under compression. The force-dependent impedance spectrogram is recorded, thus allowing one to detect any changes in the distribution of resistive and capacitive elements using a distributed time constant model, which reflect properties of the underlying nanotube network. For both high and low concentrations, a simple single-relaxation time electrical equivalent circuit with force-dependent resistance and capacitance provides a good fit to the experimental data, thus demonstrating that the distribution of resistive and capacitive remains the same during compression. This is attributed to randomly aligned clusters of carbon nanotubes. Knowing how the electrical network changes under compression is of particular importance when designing piezoresistive sensors that utilize lower concentrations of nanotubes.

Dielectric constant, AC conductivity and impedance spectroscopy of zinc-containing diamond-like carbon film UV photodetector

We report on the dielectric constant, conductivity, impedance spectroscopy and current-voltage characteristic of zinc contain diamond-like carbon (Zn-DLC) films prepared by a combination of plasma source ion implantation with magnetron sputtering of a zinc target. The frequency variation of the AC conductivity follows Jonscher's power law. The temperature variation of the frequency exponent indicates that the charge carriers follow a correlated barrier hopping conduction mechanism. The frequency dispersion of real and imaginary part of the dielectric constant obeys a modified Cole-Cole equation. The space charge conductivity, free charge conductivity and relaxation time of the Zn-DLC thin films are temperature dependent. The relaxation time decreases with increase in temperature. The Nyquist plot of complex impedance spectroscopy is simulated by a simple electrical equivalent circuit. The imaginary part of the complex impedance shows a relaxation peak, which shifts towards the high frequency side with an increase in temperature. The temperature dependent current-voltage (I-V) characteristic shows a non-linear type behaviour which follows the Poole-Frenkel (PF) emission model. To investigate the photosensitivity of an Ag/Zn-DLC/Si device, we placed it in dark and UV light condition and measured the (I-V) characteristic at room temperature. The dark current density and photocurrent density follow the PF model and a modified PF model respectively.

Real-time monitoring of a microbial electrolysis cell using an electrical equivalent circuit model.

Efforts in developing microbial electrolysis cells (MECs) resulted in several novel approachesfor wastewater treatment and bioelectrosynthesis. Practical implementation of these approaches necessitates the development of an adequate system for real-time (on-line) monitoring and diagnostics of MEC performance. This study describes a simple MEC equivalent electrical circuit (EEC) model and a parameter estimation procedure, which enable such real-time monitoring. The proposed approach involves MEC voltage and current measurements during its operation with periodic power supply connection/disconnection (on/off operation) followed by parameter estimation using either numerical or analytical solution of the model. The proposed monitoring approach is demonstrated using a membraneless MEC with flow-through porous electrodes. Laboratory tests showed that changes in the influent carbon source concentration and composition significantly affect MEC total internal resistance and capacitance estimated by the model. Fast response of these EEC model parameters to changes in operating conditions enables the development of a model-based approach for real-time monitoring and fault detection.

A ladder network modelling the electrochemical impedance of the diffusion and reaction processes in semi-infinite space.

The Gerischer impedance, i.e., the diffusion-reaction impedance of an ionic species in semi-infinite space, has been modelled by means of a novel simple equivalent ladder electric circuit constituted by a finite number of resistors and capacitors, which corresponds to the Cauer structure obtained from development into continued fractions. The Nyquist plots of the impedance of the ladder network or Cauer circuit and the deviation with respect to the Gerischer impedance have been originally analysed as a function of the number of circuit elements. From the Cauer equivalent circuit, a new and simple expression modelling the Gerischer impedance at the limit of the lowest frequencies has been derived.

Investigation of surface charge density on solid–liquid interfaces by modulating the electrical double layer

A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid–liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid–liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a dc bias voltage across the plates, an ac electric current can be generated. By measuring the voltage drop across a load resistor as a function of bias voltage, we can study the surface charge density on solid–liquid interfaces. Our experimental results agree very well with the simple equivalent electrical circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. We expect this method to aid in the study of electrical phenomena on solid–liquid interfaces.

Influence of Large-Scale Conductivity Inhomogeneities in the Atmosphere on the Global Electric Circuit

Abstract Theoretical estimation of the influence of large-scale conductivity inhomogeneities on the global electric circuit and, in particular, on the ionospheric potential is considered. A well-posed formulation of this problem is presented, on the basis of which an approximate method is developed so as to take account of large-scale conductivity inhomogeneities. Under certain restrictions imposed on the distributions of the conductivity and the external current density, explicit approximate formulas for the ionospheric potential are derived. The approximation developed is shown to be equivalent to that of classical models of atmospheric electricity in which the atmosphere is divided into two or more columns and is replaced by a simple equivalent electric circuit. The effect of conductivity inhomogeneities located inside and outside thunderclouds is discussed and, in particular, it is demonstrated that taking account of the conductivity reduction inside thunderclouds leads to a substantial increase in the ionospheric potential. The results following from the approximate theory are compared with those obtained from direct numerical simulations. It is found that the suggested approximation qualitatively accounts for the dependence of the ionospheric potential on the parameters of the conductivity distribution, although the relative error may be significant, especially in the case of a substantial reduction in the conductivity inside thunderclouds.

Characteristic Analysis on Transverse Comb Structure Using PSpice

An analysis of transverse comb structure based MEMS accelerometer is carried out. Its static and dynamic behavior is analyzed by employing a simple electrical equivalent circuit in the acceleration range of 0-30g. The device is simulated for dc, transient and frequency conditions. In the transient analysis, the device is excited with sinusoidal and step input acceleration and the proof mass displacement is evaluated. It is found that, the capacitance and displacement values obtained from our simulation matches well with reports from ANSYS Workbench®. The maximum displacement in the structure is evaluated at different condition and the effect of damping is investigated.

Synthesis, characterization and influence of electrolyte solutions on electrical properties of organic–inorganic composite membrane

In this work various electrical properties of titanium molybdate composite membrane had been discussed. The membrane was characterized by X-ray diffraction, scanning electron microscopy, particle size analysis and Infra-red spectroscopy. The effective fixed charge density of the membrane was determined by TMS method and it showed the dependence of membrane potential on, the charge on the membrane matrix, porosity and size of permeating ions. The change in membrane capacitance and resistance values with the change in electrolyte concentration and applied frequency had been interpreted in terms of the charges produced in the electrical double layer at the membrane solution interface. The magnitude of membrane capacitance had been found to be dependent on the capacitance of the double layer. In higher frequency range the impedance data evaluated on the basis of simple equivalent electrical circuit model and had been found to follow theoretical prediction. Other parameters such as transport number, distribution coefficient and charge effectiveness were also calculated.

Properties of the electrogenic activity of bacteriorhodopsin

In this study, we analyzed the photoelectric current generated by bacteriorhodopsin adsorbed on a polymer film, "Lumirror" (Muneyuki et al. in FEBS Lett 427:109-114, 1998). We could examine the photoelectric current over a wide range of light intensity and pH values using the same membrane owing to the mechanical and chemical stability of the thin polymer film. We analyzed the photoelectric current by comparison with a simple equivalent electric circuit. Analysis of experimental results obtained at different light intensities suggested that the electromotive force of the bacteriorhodopsin was independent of light intensity. The pH dependence of the photoelectric current suggested that the bacteriorhodopsin could generate a maximum electromotive force at approximately pH 6.

Investigation of Passive Film Properties and Pitting Resistance of AISI 316 in Aqueous Ethanoic Acid Containing Chloride Ions using Electrochemical Impedance Spectroscopy(EIS)

The structure and properties of the passive film formed on the surface of AISI 316 stainless steel in aqueous ethanoic acid have been investigated using EIS. Experiments were carried out at 30 oC in different concentrations of ethanoic acid. Effects on the film properties due to the change of electrode potential, exposure durations and addition of chloride ions to the electrolyte were also studied. Impedance parameters were determined using simple model and equivalent electrical circuit. Results suggest the formation of multilayered passive film on the steel surface. The film possessed dual structure. Inner layers were thin and compact, whereas the outer layer was porous and defective. The measured capacitive behavior was of non ideal nature and hence replaced by constant phase element or CPE. Formation of the passive film and the change in its structure has been explained using impedance parameters.

A critical assessment of the Mott-Schottky analysis for the characterisation of passive film-electrolyte junctions

The widespread use of the Mott-Schottky plots to characterize the energetics of passive film/electrolyte junction is critically reviewed in order to point out the limitation of such approach in describing the electronic properties of passive film as well in deriving the correct location of the characteristic energy levels of the junction. The frequency dependency of M-S plots frequently observed in the experimental data gathered in a sufficiently large range of frequency is extensively discussed for a relatively thick (160 nm) thermally aged amorphous niobia (α-Nb2O5) film immersed in electrolytic solution. The relatively simple equivalent electrical circuit describing an ideally blocking behaviour of the junction allows a direct comparison of the experimental data analysis based on the use of Mott-Schottky or amorphous semiconductor Schottky barrier interpretative models. Moreover the theoretical simulations of the M-S plots based on the theory of crystalline semiconductor suggest an electronic structure of the investigated passive film containing a distribution of localized electronic states deep lying in energy in agreement with the model of amorphous semiconductor Schottky barrier.

Electrochemical Impedance Spectroscopy of PEM Fuel Cell with Metal Bipolar Plates

Proton exchange membrane fuel cell (PEMFC) with metal bipolar plates has many problems for commercial application such as an increase of contact resistance of bipolar plates due to growth of passive film. In this study, electrochemical impedance spectroscopy (EIS) was employed to evaluate PEMFC performance. The EIS of PEMFC was successfully measured and can be explained by simple electrical equivalent circuit. It was found that using impedance at high frequency, the contact resistance can be evaluated.

Generalized serial dilution module for monotonic and arbitrary microfluidic gradient generators

In this paper, we propose a generalized serial dilution module for universal microfluidic concentration gradient generators including N cascaded-mixing stages in a stepwise manner. Desired concentrations were generated by means of controlled volumetric mixing ratios of two merging solutions in each stage. The flow rates were adjusted by controlling channel length, which is proportional to fluidic resistance in each channel. A generalized mathematical model for generating any complex concentration and output flow rate gradients is presented based on the fact that there is an analogy between microfluidic circuits and electrical circuits. The pressure drop corresponds to a voltage drop, the flow rate to an electrical current, and the flow resistance to an electrical resistance. A simple equivalent electrical circuit model was generalized, and in the model each channel segment was represented by an electrical resistance. As a result of the mathematical modelling, the only variable parameter in the generalized serial dilution module was the channel length. By the use of the generalized serial dilution module with N = 4, three types of microfluidic gradient generators for linear, logarithmic and Gaussian gradients were successfully designed and tested. The proposed strategy is capable of generating universal monotonic gradients with a single module or arbitrary gradients with multiple modules ranging from linear to complex non-linear shapes of concentration gradients as well as arbitrary output flow rate gradients in a stepwise manner. The simple universal gradient generation technology using the generalized serial dilution module will find widespread use in the greater chemical and biological community, and address many challenges of gradient-dependent phenomena.

Thermal Modeling of Dry-Transformers and Estimating Temperature Rise

Temperature rise in a transformer depends on variety of parameters such as ambient temperature, output current and type of the core. Considering these parameters, temperature rise estimation is still complicated procedure. In this paper, we present a new model based on simple electrical equivalent circuit. This method avoids the complication associated to accurate estimation and is in very good agreement with practice. Keywords—Thermal modeling, temperature rise, equivalent thermal circuit.

A Novel Approach to Modeling and Simulation of NTC Thick-Film Segmented Thermistors for Sensor Applications

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes the design, modeling, simulation, and fabrication of thick-film segmented thermistors. These thermistors were printed on alumina using negative temperature coefficient 3K3 paste, composed of nanometer powder. Their room temperature resistance was measured versus the number of segments and electrode surface value for the fixed layer thickness and electrode spacing. After that, very large thermistors were printed to serve as both the powerful self-heaters and the heat loss sensors in the thermistor volume air flow meter and anemometer. For an application in AC bridges, impedance Z(f) and insertion loss S21 [dB] of the same largest segmented thermistor were measured using network analyzer HP8752A. Impedance modeling was performed using simple equivalent electrical circuit with circuit parameters estimated by fitting procedure (traditional approach), as well as using a commercial electromagnetic simulation program microwave office (MWO, novel approach). This was followed by the modeling of electrical current distribution over a number of segments done within the MWO. The results obtained from simulations and measurements were mutually compared. </para>

Systematic Study of the Dopant-Dependent Properties of Electrically Programmable Fuses With Silicided Poly-Si Links Through a Series of $I$– $V$ Measurements

Electrically programmable/writable fuses (e-fuses) with a Ni-silicided polycrystalline silicon narrow link and fabricated with four doping conditions were studied using two successive I-V measurements. The initial I-V sweeps can change e-fuses into targeted programmed states and display all of the programming processes where the currents change by many orders of magnitude. The second set of I-V curves can show stability and conduction in the programmed states for both bias polarities. Through the series of I-V measurements, the two-step programming with moderate blowing conditions could be reproduced and studied systematically. The programming processes of incompletely programmed states, before complete programming (CP), were found to be strongly dependent on the dopant conditions. The origin of the dopant dependency was considered within a simple electrical equivalent circuit model. At least two or three programmed states were identified among the completely programmed states in terms of the characteristic spreads of the final resistance and conduction behavior. The most distinctive currents after CP are similar to those in varistors. The stability of every programmed state is strongly dependent on the dopant conditions.