Simple Electrical Model Research Articles

Modeling and Validation of a Lithium-Ion Battery Pack

Abstract Batteries are part of an extremely nonlinear electrochemical system, and their performance is determined by various key factors such as law of thermodynamics, electrode kinetics, ion transport, and diffusion. To develop an accurate model of a battery, it is important to take into consideration both the internal and external conditions that would determine both the battery dynamics and its performance. Electrochemical, mathematical, and electrical equivalent circuit models are three common ways to model the electrochemical battery system. However, using these models involves certain limitations such as increased computation, empirical equations, and components (both active and passive). A simple electrical battery model with a voltage source and a resistor is insufficient to attain the desired level of accuracy in the model. To overcome these limitations, this study presents an electrothermal model that has been designed by adding “n” number of resistance capacitance (RC) pairs connected parallelly to ensure both dynamics and accuracy. An electrothermal model of a lithium-ion cell with a one-RC model and two-RC model has been developed, and a performance comparison has also been made to check the voltage accuracy of all the models. The electrical and thermal parameters (Em (state of charge [SOC], T), RO (SOC, T), R1 (SOC, T), R2 (SOC, T), C1 (SOC, T), C2 (SOC, T)) required for an RC model have been extracted through the pulse charge-discharge test. A battery pack of 55 V, 50 Ah using the RC model based on the Indian driving cycle condition has also been developed. Pulse charge-discharge and constant current-constant voltage profiles have been applied to the developed battery pack model to simulate and validate the accuracy of voltage in a real-time scenario.

Algae–water–silica interactions in low and high ionic strength environments

The interaction between algae and solid surfaces is of direct interest for the optimization of biofuel production technologies. Silica is particularly relevant due the use of solgel matrices for enhanced growth and ease of processing, where ionic strength variation is an important consideration. Here, an inverted fluorescence experiment is used to perform measurements of the distance between a silica surface and algae in solution. At low ionic strength, the average algae–silica distance is approximately 90 nm but increases to roughly 130 nm at 1 M NaCl, contradicting the prediction based on simple electrical double layer interaction models. These findings illustrate the role of biochemical and electrostatic interactions at charged aqueous interfaces of relevance to biofuel production.

Changes Over Time in the Electrode/Brain Interface Impedance: An Ex-Vivo Study.

Closed-loop neural implants based on continuous brain activity recording and intracortical microstimulation are extremely effective and promising devices to monitor and address many neurodegenerative diseases. The efficiency of these devices depends on the robustness of the designed circuits which rely on precise electrical equivalent models of the electrode/brain interface. This is true in the case of amplifiers for differential recording, voltage or current drivers for neurostimulation, and potentiostats for electrochemical bio-sensing. This is of paramount importance, especially for the next generation of wireless and ultra-miniaturised CMOS neural implants. Circuits are usually designed and optimized considering the electrode/brain impedance with a simple electrical equivalent model whose parameters are stationary over time. However, the electrode/brain interfacial impedance varies simultaneously in frequency and in time after implantation. The aim of this study is to monitor the impedance changes occurring on microelectrodes inserted in ex-vivo porcine brains to derive an opportune electrode/brain model describing the system and its evolution in time. In particular, impedance spectroscopy measurements have been performed for 144 hours to characterise the evolution of the electrochemical behaviour in two different setups analysing both the neural recording and the chronic stimulation scenarios. Then, different equivalent electrical circuit models have been proposed to describe the system. Results showed a decrease in the resistance to charge transfer, attributed to the interaction between biological material and the electrode surface. These findings are crucial to support circuit designers in the field of neural implants.

Application of the Extrapolation Method in Battery Diagnostics for Electric Vehicles

In a lithium-ion battery, the crossing of its charging–discharging curves represents an unambiguous current capacity. The reproduction of a complete charging–discharging cycle defines the maximum possible charge for a current battery state. When obtaining of the curves experimentally, one should consider the duration of polarization or depolarization. It is reported that the battery capacity depends considerably on the value of the battery’s internal resistance as this value defines the location of the actual charging–discharging curves relative to the nominal curves, i.e., the point of their crossing shifts. The present study aimed to develop a diagnostic algorithm for the batteries of electric vehicles for a complete charge–discharge cycle, considering the processes of polarization and depolarization. The mathematical expressions for determining the internal resistance and the complete charge of the battery were obtained. The novelty of the present study is in the fact that by applying extrapolation to a simple electrical model of a lithium-ion battery, the degree of degradation and the current charge could be predicted without the requirement of lengthy experimental procedures.

A Spherical “Earth–Ionosphere” Model for Deep Resource Exploration Using Artificial ELF-EM Field

Fully coupled lithosphere, atmosphere, and ionosphere theory has demonstrated that extremely low-frequency electromagnetic (ELF-EM) fields present a broad application prospect in deep resource exploration, but previous studies have ignored the contribution of the Earth’s curvature. This study extends the theory of ELF-EM over a stratified Earth to the case where the Earth’s curvature must be taken into account, and presents an analytical solution of the ELF-EM field excited by a grounded horizontal antenna in a spherical Earth–ionosphere model, whose theoretical approach and solution method are notably different from the flat Earth–ionosphere model. Additionally, the Earth is treated as a concentric-layered sphere rather than an ideal homogeneous sphere. We aim to investigate the effects of the Earth’s curvature on the surface field, so as to broaden the coverage of the ELF wave in resource exploration. The solution is mathematically accurate and physically reasonable, since it reflects the sphericity and radially stratified structure of the Earth. We first verify the correctness and reliability of the proposed method by comparing the results with FDTD in a full-space spherical model. Additionally, we then compared the spherical results with the conventional controlled-source electromagnetic method and flat Earth–ionosphere results. The results show that when the distance between the transmitter and the receiver is comparable to the Earth radius, the spherical model better reflects the resonance of the wave in the cavity, suggesting that the effect of the Earth’s curvature is not negligible. Then, the numerical simulations conducted to investigate the properties of the EM fields and their sensitivities to the conductivity at depth in the Earth are discussed. Finally, the EM responses of some simple electrical conductivity structures models are modeled to illustrate their prospects in future resource exploration.

Modeling implanted metals in electrical stimulation applications

Objective. Metal implants impact the dosimetry assessment in electrical stimulation techniques. Therefore, they need to be included in numerical models. While currents in the body are ionic, metals only allow electron transport. In fact, charge transfer between tissues and metals requires electric fields to drive electrochemical reactions at the interface. Thus, metal implants may act as insulators or as conductors depending on the scenario. The aim of this paper is to provide a theoretical argument that guides the choice of the correct representation of metal implants in electrical models while considering the electrochemical nature of the problem Approach. We built a simple model of a metal implant exposed to a homogeneous electric field of various magnitudes. The same geometry was solved using two different models: a purely electric one (with different conductivities for the implant), and an electrochemical one. As an example of application, we also modeled a transcranial electrical stimulation (tES) treatment in a realistic head model with a skull plate using a high and low conductivity value for the plate. Main results. Metal implants generally act as electric insulators when exposed to electric fields up to around 100 V m−1 and they only resemble a perfect conductor for fields in the order of 1000 V m−1 and above. The results are independent of the implant’s metal, but they depend on its geometry. tES modeling with implants incorrectly treated as conductors can lead to errors of 50% or more in the estimation of the induced fields Significance. Metal implants can be accurately represented by a simple electrical model of constant conductivity, but an incorrect model choice can lead to large errors in the dosimetry assessment. Our results can be used to guide the selection of the most appropriate model in each scenario.

Electrical impedance measurement system to assess in-situ experiments on epithelia under ELF magnetic fields exposure

Purpose: The development of an electric impedance meter based on the impedance spectroscopy technique, for in vitro and in situ experimentation, with cellular epithelia submitted to extremely low frequency magnetic fields in a controlled environment. Unlike other reported systems, a strength of the one presented here is that it avoids the influence of external factors on the experiment. Materials and methods: The designed system employs the electrical impedance values obtained by the impedance spectroscopy technique to determine the parameters of the simple equivalent electrical model of a cellular monolayer. The Madin-Darby Canine Kidney (MDCK) cell cultures were used as subjects of study in the experimental protocol. Results: The validation was carried out by comparing the transepithelial electrical impedance data of the cell cultures obtained with the developed system and those of the Cellzscope® commercial system used as the standard. Non-significant differences were obtained. Conclusion: It was confirmed that the developed system provides reliable values of transepithelial electrical impedance to experiment with cell cultures and take advantage of the controlled environment to reduce the effects of experimental management.

K+-dependent Müller cell-generated components of the electroretinogram.

The electroretinogram (ERG) has been employed for years to collect information about retinal function and pathology. The usefulness of this noninvasive test depends on our understanding of the cell sources that generate the ERG. Important contributors to the ERG are glial Müller cells (MCs), which are capable of generating substantial transretinal potentials in response to light-induced changes in extracellular K+ concentration ([K+]o). For instance, the MCs generate the slow PIII (sPIII) component of the ERG as a reaction to a photoreceptor-induced [K+]o decrease in the subretinal space. Similarly, an increase of [K+]o related to activity of postreceptor retinal neurons also produces transretinal glial currents, which can potentially influence the amplitude and shape of the b-wave, one of the most frequently analyzed ERG components. Although it is well documented that the majority of the b-wave originates from On-bipolar cells, some contribution from MCs was suggested many years ago and has never been experimentally rejected. In this work, detailed information about light-evoked [K+]o changes in the isolated mouse retina was collected and then analyzed with a relatively simple linear electrical model of MCs. The results demonstrate that the cornea-positive potential generated by MCs is too small to contribute noticeably to the b-wave. The analysis also explains why MCs produce the large cornea-negative sPIII subcomponent of the ERG, but no substantial cornea-positive potential.

Impedance model for voltage optimization of parabens extraction in an electromembrane millifluidic device

In sample pre-treatment, millifluidic electromembrane platforms have been developed to extract and pre-concentrate target molecules with good clean-up that minimize matrix effects. Optimal operation conditions are normally determined experimentally, repeating the extractions at different conditions and determining the efficiencies by an analytical technique. To shorten and simplify the optimization protocol, millifluidic platforms have been electrically characterized by impedance spectroscopy. The magnitude of the resistance of the electromembrane has been found very predictive of the migration capacity and extraction efficiency of three different parabens on real time. The optimal conditions (4 V of applied potential) (Electromembrane extraction low voltage) have been successfully applied in the extraction of parabens from urine samples, that not only improves the extraction efficiency (100% for all compounds) but also provides a very low current intensity (7 µA), which is very important in electromembrane to minimize electrolysis phenomena. The possibility to optimize one of the most critical and important parameters such as the voltage with a simple electrical model may accelerate the production of application-specific millifluidic electromembrane platforms in a short development time. The results showed that millifluidic electromembrane extraction based low voltage has a future potential as a simple, selective, and time-efficient sample preparation technique allowing a simple battery as power supply.

Electrical Model of Phase-to-Woodpole Bird Electrocution

The electrocution of large birds such as eagles and vultures when making simultaneous contact between a phase conductor and the top of a pole on medium voltage woodpole distribution lines is addressed. System (phase-to-phase) voltages of 11 kV, 22 kV and 33 kV are covered. This phenomenon has been investigated by measurement of the resistance of poles used in the field, as well as measurement of the impedance of recently deceased birds. This has previously been used to compile a simple electrical model for 22 kV systems. This paper compiles a detailed model that is used to estimate the risk posed to large birds by this mode of electrocution for all three voltage levels. The results show that only a few scenarios exist whereby a bird may be at risk, which ties in with field experience. Details of how the wood and bird resistance was measured are also included, as are details of calculations performed.

Impact of Current Flow Diverter on Innovative HTS Tape Architectures for DC Fault Current Limitation at Electric Fields up to 150 V/m

In this work, we use numerical simulations to compare the performance of different promising architectures of HTS tape for DC fault current limitation. A 1-D finite-element model which solves the heat equation through the thickness of a high-temperature superconducting (HTS) tape at the location of a hot spot was coupled with a simple electrical circuit model to perform the simulations. Using the normal zone propagation velocity (NZPV) obtained from a distinct 3-D finite-element electrothermal model, the quench dynamics in HTS tapes can be predicted, which allows estimating quite accurately the fault current level vs time. The calculations indicate that the insertion of a current flow diverter in the tape architecture allows decreasing the fault current level more rapidly and reducing the temperature elevation, thanks to the increased NZPV.

Establishing the Input Impedance Requirements of ECG Recording Amplifiers

The transient response of electrocardiogram (ECG) amplifiers is investigated in the light of the IEC 60601 performance standard for electrocardiographs. Simulations and bench tests carried out on models of several electrodes reveal that the undershoot limit of $100~\mu \text{V}$ and the recovery slope limit of 300 $\mu $ Vs−1 in response to a narrow 3-mV, 100-ms rectangular pulse are violated when the recommended input impedance of 10 $\text{M}\Omega $ is used in the amplifier. Analyses of dc and ac coupling of the electrodes to the amplifier are carried out, and the constraints are established for the amplifier input impedance based on the electrical properties of the electrodes. We recommend that the amplifier input resistance needs to be determined as $\text{R}_{\mathrm {in}} >60\text{R}_{P}$ or $>25/{\text{C}}_{P}$ , whichever is greater, where ${\text{R}}_{P}$ and $\text{C}_{P}$ are the resistance and capacitance of a simple electrical model of the electrode. In the case of ac coupling of the electrode to the amplifier, $\text{C}_{C}\text{R}_{\mathrm {in}} > 6$ s, where ${\text{C}}_{C}$ is the coupling capacitor. The results of simulations and tests suggest that an amplifier input impedance exceeding 3 $\text{G}\Omega $ and a cutoff frequency no higher than 0.05 Hz are necessary in order to meet the IEC 60601 performance criteria and avoid distortion of the recorded ECG signal.

Conduction mechanisms and voltage drop during field electron emission from diamond needles

We report results of experimental investigation of field electron emission from diamond nanoemitters. The measurements were performed with single crystal diamond needles fixed at tungsten tips. The voltage drop along diamond needles during emission was revealed and measured using electron energy spectroscopy. The observed linear dependence of the voltage drop in diamond on voltage applied to the tungsten tip is explained in the frame of a simple macroscopic electrical model combining Poole–Frenkel conduction along the diamond tip and Fowler–Nordheim tunneling at the diamond-vacuum junction. Experimental evidences of electron emission sensitivity to laser illumination are discussed for possible modification of diamond emitter characteristics and voltage drop.

Impedance Characterization of an LCO-NMC/Graphite Cell: Ohmic Conduction, SEI Transport and Charge-Transfer Phenomenon

Currently, Li-ion cells are the preferred candidates as energy sources for existing portable applications and for those being developed. Thus, a proper characterization of Li-ion cells is required to optimize their use and their manufacturing process. In this study, the transport phenomena and electrochemical processes taking place in LiCoO2-Li(NiMnCo)O2/graphite (LCO-NMC/graphite) cells are identified from half-cell measurements by means of impedance spectroscopy. The results are calculated from current densities, instead of absolute values, for the future comparison of this data with other cells. In particular, impedance spectra are fitted to simple electrical models composed of an inductive part, serial resistance, and various RQ networks—the parallel combination of a resistor and a constant phase element—depending on the cell. Thus, the evolution of resistances, capacitances, and the characteristic frequencies of the various effects are tracked with the state-of-charge (SoC) at two aging levels. Concretely, two effects are identified at the impedance spectrum; one is clearly caused by the charge transfer at the positive electrode, whereas the other one is presumably caused by the transport of lithium ions across the solid electrolyte interphase (SEI) layer. Moreover, as the cells age, the characteristic frequency of the charge transfer is drastically reduced by a factor of around 70%.

From the basic science of biological effects of ultrashort electrical pulses to medical therapies

This article is based on my presentation at the D'Arsonval Ceremony at the Joint Annual Meeting of the Bioelectromagnetics Society and the European BioElectromagnetics Association in Hangzhou, China, in June of 2017. It describes the pathway from the first studies on the effects of intense, nanosecond pulses on biological cells to the development of medical therapies based on these effects. The motivation for the initial studies of the effects of high voltage, nanosecond pulses on mammalian cells was based on a simple electrical circuit model, which predicted that such pulses allow us to affect not just the plasma membrane but also the subcellular structures. The first experimental study that confirmed this hypothesis was published in 2001 in the Bioelectromagnetics journal. It was followed by a large number of publications that showed that such ultrashort pulses affect cell functions, such as programmed cell death, and, at lower intensity, calcium mobilization from intracellular structures. These basic studies were leading to novel cancer treatments, treatments of cardiac arrhythmia, and advanced wound healing. Further, by reducing the pulse duration into the picosecond range, antenna-based neural stimulation seems to be possible. This manuscript gives an overview of the progress in this field of research in the decade after the initial bioelectric studies with high-voltage, nanosecond pulses, particularly the research performed at the Frank Reidy Research Center for Bioelectrics. It also tells you about my journey and that of my colleagues at the Center for Bioelectrics into and through this fascinating bioelectromagnetics research area. Bioelectromagnetics. 39:257-276, 2018. © 2018 Wiley Periodicals, Inc.

Insights into the energy storage mechanism of hybrid supercapacitors with redox electrolytes by Electrochemical Impedance Spectroscopy

Recently, new electrode materials and electrolytes for hybrid supercapacitors with enhanced performance have been extensively studied. However, the energy storage mechanism of these hybrid devices has not been assessed in detail. In this sense, Electrochemical Impedance Spectroscopy is one of the most powerful techniques to better understand the physicochemical phenomena involved in this new kind of supercapacitors. In this work, Impedance Spectroscopy was used for the first time to analyse the energy storage mechanism in supercapacitors with non-aqueous electrolytes with organic redox molecules dissolved, as a function of the frequency and bias voltage. In addition, a simple electrical model has been developed to describe the behavior of the supercapacitor with a very good correlation with the experimental results. This investigation provides useful information delving into the behavior of the devices which is fundamental for their future practical applications.

Conversion of descriptor representations to state-space form: an extension of the shuffle algorithm

ABSTRACTThis paper proposes a systematic procedure for the determination of state-space models from an available descriptor representation of a linear dynamic system. The goal is to determine a state equation, a set of algebraic equations and an output equation in terms of the state and input variables. It is shown that standard methods may fail to convert the descriptor representation to state-space form, even for simple electrical circuit models obtained from Kirchoff's laws and constitutive element equations. A novel procedure to address this problem is then proposed as an extension of the classic shuffle algorithm combined with a singular value decomposition approach. In addition to an illustrative example involving a simple electrical circuit, the proposed method is employed in a case study involving the modelling of three-dimensional RLC networks with a large number of components.

Magnitude and behavior of cross-talk effects in multichannel electrophysiology experiments

Modern neurophysiological experiments frequently involve multiple channels separated by very small distances. A unique methodological concern for multiple-electrode experiments is that of capacitive coupling (cross-talk) between channels. Yet the nature of the cross-talk recording circuit is not well known in the field, and the extent to which it practically affects neurophysiology experiments has never been fully investigated. Here we describe a simple electrical circuit model of simultaneous recording and stimulation with two or more channels and experimentally verify the model using ex vivo brain slice and in vivo whole-brain preparations. In agreement with the model, we find that cross-talk amplitudes increase nearly linearly with the impedance of a recording electrode and are larger for higher frequencies. We demonstrate cross-talk contamination of action potential waveforms from intracellular to extracellular channels, which is observable in part because of the different orders of magnitude between the channels. This contamination is electrode impedance-dependent and matches predictions from the model. We use recently published parameters to simulate cross-talk in high-density multichannel extracellular recordings. Cross-talk effectively spatially smooths current source density (CSD) estimates in these recordings and induces artefactual phase shifts where underlying voltage gradients occur; however, these effects are modest. We show that the effects of cross-talk are unlikely to affect most conclusions inferred from neurophysiology experiments when both originating and receiving electrode record signals of similar magnitudes. We discuss other types of experiments and analyses that may be susceptible to cross-talk, techniques for detecting and experimentally reducing cross-talk, and implications for high-density probe design.NEW & NOTEWORTHY We develop and experimentally verify an electrical circuit model describing cross-talk that necessarily occurs between two channels. Recorded cross-talk increased with electrode impedance and signal frequency. We recorded cross-talk contamination of spike waveforms from intracellular to extracellular channels. We simulated high-density multichannel extracellular recordings and demonstrate spatial smoothing and phase shifts that cross-talk enacts on CSD measurements. However, when channels record similar-magnitude signals, effects are modest and unlikely to affect most conclusions.

Interface Trap State Characterization of Metal-Insulator-Semiconductor Structures Based on Photosensitive Organic Materials

Flexible organic and printed electronics has led in the last years to exciting applications, especially for what concerns devices incorporating photosensitive materials. Among the latter, organic field-effect phototransistors are a promising technology because of the high light-sensitivity and the possibility of being integrated within more complex systems. Nevertheless, their optimization has not been thoroughly investigated and considerable variations are often observed in their behavior. In this framework, the most critical aspect is represented by the interface formed between the organic semiconductor and the employed dielectric layer. In our contribution, we have fabricated metal-insulator-semiconductor (MIS) structures based on the archetypal photosensitive organic materials poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) on Silicon/SiO2 substrates, exploiting their blend in a bulk heterojunction configuration. The MIS structures have been characterized by means of admittance spectroscopy to study the properties of the trap distribution at the interface between the organic semiconductors and the silicon oxide insulating layer. The complex behavior of the capacitance and loss diagrams has been interpreted with a simple electrical model to extract the density of the traps at the interface between the insulator and the semiconductor. It is shown that in the blend-based MIS device several peaks arise in the loss diagram with respect to the only P3HT MIS device. This could be attributed to a different interaction between the single species in the bulk heterojunction and the silicon oxide layer. Furthermore, the reported values of trap densities result in the range of those determined for analogous structures and materials.

Characterization and Modeling of a Hybrid-Electric-Vehicle Lithium-Ion Battery Pack at Low Temperatures

Although lithium-ion batteries have penetrated hybrid electric vehicles (HEVs) and pure electric vehicles (EVs), they suffer from significant power capability losses and reduced energy at low temperatures. To evaluate those losses and to make an efficient design, good models are required for system simulation. Subzero battery operation involves nonclassical thermal behavior. Consequently, simple electrical models are not sufficient to predict bad performance or damage to systems involving batteries at subzero temperatures. This paper presents the development of an electrical and thermal model of an HEV lithium-ion battery pack. This model has been developed with MATLAB/Simulink to investigate the output characteristics of lithium-ion batteries over the selected operating range of currents and battery capacities. In addition, a thermal modeling method has been developed for this model so that it can predict the battery core and crust temperature by including the effect of internal resistance. First, various discharge tests on one cell are carried out, and then, cell's parameters and thermal characteristics are obtained. The single-cell model proposed is shown to be accurate by analyzing the simulation data and test results. Next, real working conditions tests are performed, and simulation calculations on one cell are presented. In the end, the simulation results of a battery pack under HEV driving cycle conditions show that the characteristics of the proposed model allow a good comparison with data from an actual lithium-ion battery pack used in an HEV.