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In the automotive industry, ageing mechanisms and diagnosis of Li-ion batteries depending on charge rate are of tremendous importance. With this in mind, we have investigated the lifetime degradation of lithium-ion battery cells at three distinct charging rates using Electrochemical Impedance Spectroscopy (EIS). Impedance spectra of high-energy Panasonic NCR18650B batteries have been analysed in light of two distinct approaches, namely the time-dependent evaluation of the Constant Phase Element (CPE), and the single parameter investigation of resonance frequency of the circuit. SOH percentages were used to validate our approach. By monitoring the CPE-Q parameter at different charge rates of 0.5 C, 1 C, and 1.5 C, respectively, we applied a degradation speed analysis, allowing us to predict a quantitative value of the LIBs. The results are in complete agreement with the resonance frequency single parameter analysis, in which quite a similar trend was obtained after the spline fitting. [ABSTRACT FROM AUTHOR]

As electrochemical research undergoes rapid technological progression, the acquisition of substantial amounts of electrochemical impedance spectra (EIS) becomes increasingly feasible. Yet, this advancement introduces intricate challenges in data processing, automation, and interpretation. This paper delves into the sufficiency of unsupervised machine learning (ML) and in particular dimensionality reduction methods in decoding EIS complexities, examining its strengths, limitations, and potential pathways for optimization. As we navigated the intricacies of non‐linear dimensionality reduction, spotlighting t‐distributed stochastic neighbor embedding (t‐SNE) and uniform manifold approximation and projection (UMAP) algorithms, a pattern emerged: these techniques excel at categorizing divergent impedance spectra but show limitations when faced with analogous circuit configurations, especially those substituting a capacitor with a constant phase element. This observation not only underscores a limitation but also accentuates that unsupervised ML approaches, alone, may not fully unravel the nuances of EIS spectra. In the concluding section of our manuscript, we discuss the implications of this finding from a practical standpoint, particularly for electrochemists seeking to apply these methods in their work. [ABSTRACT FROM AUTHOR]

Ageing of rechargeable batteries is routinely characterized in the frequency domain by electrochemical impedance spectroscopy, but the technique requires laboratory measurements to be made on a time scale of days. However, the normal cycling of a battery as it is used in situ provides equivalent information in the time domain, though extracting robust frequency information from a time series is challenging. In this work, we explore, in the time domain, the relationship between instantaneous voltage-current phase difference and cycle efficiency. Moreover, we demonstrate that phase measures can be used to identify battery ageing. We have cycled a 250 mA h Nickel-Cobalt cell several hundred times and used Hilbert Transforms to identify phase difference between voltage and current. This phase difference becomes closer to zero as the battery ages, commensurate with a drop in energy cycle efficiency. In another experiment, we applied a synthetic current profile mimicking behaviour of an electric car cell, to a 3.2 A h LiNiMnCoO2 cell, for ~100 days. For this more complicated profile with a wide range of frequency content, we used wavelet analysis to identify changes in phase difference and impedance as the battery aged. For this cell, drop in cycle efficiency was associated with a rise in internal resistance. The results imply that time-series analysis of in situ measurements of voltage and current, when applied with equivalent circuit models and underlying theory, can identify markers of battery ageing.

Abstract As electrochemical research undergoes rapid technological progression, the acquisition of substantial amounts of electrochemical impedance spectra (EIS) becomes increasingly feasible. Yet, this advancement introduces intricate challenges in data processing, automation, and interpretation. This paper delves into the sufficiency of unsupervised machine learning (ML) and in particular dimensionality reduction methods in decoding EIS complexities, examining its strengths, limitations, and potential pathways for optimization. As we navigated the intricacies of non‐linear dimensionality reduction, spotlighting t‐distributed stochastic neighbor embedding (t‐SNE) and uniform manifold approximation and projection (UMAP) algorithms, a pattern emerged: these techniques excel at categorizing divergent impedance spectra but show limitations when faced with analogous circuit configurations, especially those substituting a capacitor with a constant phase element. This observation not only underscores a limitation but also accentuates that unsupervised ML approaches, alone, may not fully unravel the nuances of EIS spectra. In the concluding section of our manuscript, we discuss the implications of this finding from a practical standpoint, particularly for electrochemists seeking to apply these methods in their work.

In the automotive industry, ageing mechanisms and diagnosis of Li-ion batteries depending on charge rate are of tremendous importance. With this in mind, we have investigated the lifetime degradation of lithium-ion battery cells at three distinct charging rates using Electrochemical Impedance Spectroscopy (EIS). Impedance spectra of high-energy Panasonic NCR18650B batteries have been analysed in light of two distinct approaches, namely the time-dependent evaluation of the Constant Phase Element (CPE), and the single parameter investigation of resonance frequency of the circuit. SOH percentages were used to validate our approach. By monitoring the CPE-Q parameter at different charge rates of 0.5 C, 1 C, and 1.5 C, respectively, we applied a degradation speed analysis, allowing us to predict a quantitative value of the LIBs. The results are in complete agreement with the resonance frequency single parameter analysis, in which quite a similar trend was obtained after the spline fitting.

In an ordinary time-varying capacitor, there is debate on whether a time-domain multiplication or a time-domain convolution of capacitance and voltage determines charge. The objective of this work is to resolve this question by experiments on a time-varying capacitor in parallel with a resistor. It was implemented by a motor-driven potentiometer and op-amps. The response matched a power-law function over about two decades of time, and not an exponential, for several sets of parameters. This confirms the time-domain multiplication model. This result is the opposite of that obtained for a constant phase element (CPE) in its common time- and frequency-varying capacitor interpretation. This demonstrates that a CPE is fundamentally different from an ordinary time- and frequency-varying capacitor. [ABSTRACT FROM AUTHOR]

• Electronic properties of a-Si:H/c-Si heterojunction solar cells are investigated. • Impedance spectra of cell are best modelled by including a dispersion element. • Constant phase element behaviour is assigned to trap levels at junction interface. • Under illumination, a distinct dynamic process is observed from cell. In this article, the electronic properties of a-Si:H/c-Si heterojunction (SHJ) solar cells are analyzed by performing impedance spectroscopy (IS) characterization in the dark and under controlled illuminations. Various dynamic electrical processes occurring at different time scales, ranging from microseconds to milliseconds, are observed mainly in the operating regime of the device. Several distinct characteristics are observed: a) time constant distribution characteristic of the disordered junction, b) typical bias voltage and illumination intensity dependence of the recombination time constant, and c) an additional time constant indicative of a fast process, which appears only under illumination. The impedance spectra of the SHJ cell are best modelled by including a dispersion element, the constant phase element (CPE), in place of a pure capacitor, in its small signal electrical equivalent circuit (EEC), aside from the pure resistive and capacitive elements arranged in a simple configuration. The CPE behavior is assigned to the complex small signal response originating from the distribution of trap levels in the disordered p+-a-Si:H/n-Si heterojunction. Under illumination, a distinct dynamic process is observed compared to the dark condition in the impedance spectra of the device. The variation of the dispersion parameter, resistances, capacitance, and time constants with external stimuli is discussed. In particular, the variation of the recombination time constant with bias is remarkable under different illumination intensities due to the change in the quasi-fermi levels splitting. [ABSTRACT FROM AUTHOR]

Electrochemical impedance spectroscopy (EIS) is a widely used method for monitoring coatings because it can be done in situ and causes little damage to the coating. However, interpreting the impedance data from coatings in order to determine the state of the coating and its protective abilities is challenging. A modified version of the rapid electrochemical assessment of paint (REAP) equivalent circuit is developed here, along with a method to calculate the impedance of a circuit using matrix algebra. This new equivalent circuit and the calculation method are used to analyze EIS data obtained from a two-layer commercial organic coating system immersed in NaCl solutions with different concentrations and at different temperatures. The matrix calculation method is validated by comparing results obtained from commercial analysis software to this method for two different equivalent circuits, and the parameter values are nearly equal. Physics-based models of the equivalent circuit elements are derived and used to obtain both initial estimates for the regressions and physics-based constraints on the model parameters. These models are integrated into the regression procedure, and the corrected Akaike information criterion (AICc) is used to compare fits between the new circuit and classic equivalent circuits. The AICc values indicate the new circuit results in better fits than classic equivalent circuits used for coatings analysis. [ABSTRACT FROM AUTHOR]

Constant phase elements (CPEs) are commonly used in bioelectronic systems, to model the impedance of bioelectrodes and electrode-electrolyte interfaces. To simulate the systems with an electronic design automation tool, a circuit-simulator-compatible model of the CPE is required to use bioelectrodes in circuit simulation. This paper applies rational function approximation to the impedance of CPEs as a function of frequency, which is able to be implemented with Verilog-A language. In comparison to previously published works which simply approximate a CPE into several serially connected RCs, our work illustrates the theoretical basis behind the approximation with RCs and provides a method perform the approximation, thus resulting in a smaller relative root mean square error of impedance magnitude and phase (4 orders of magnitude lower using 25 RCs) within a bounded frequency range. To validate the model accuracy, it is applied to the modeling of human cochleae, with the simulated results correlating well with the measured results. Furthermore, this model is implemented in a circuit that includes a bioelectrode and a thin-film transistor switch, showing the capability for circuit simulation with CPEs.

The study of the induction periods of hydration and structure formation of cement stone is one of the most urgent problems of modern building materials science. Water and aqueous solutions of inorganic salts are the most widespread forms of mixing liquids for cement systems. The properties of distilled water and aqueous solutions of sodium chloride with different concentrations have been investigated by dielectrometry. It is proposed to consider the structural organization of water and aqueous solutions as a combination of strongly and weakly bound water. The strongly bound water is the result of manifestation of hydrogen bond forces; this type of water specifies the ordered state of the system. Weakly bound water causes fragmentation of the initial water continuum into smaller structural units. The change in the impedance and admittance spectra of cement paste during hardening has been analyzed. Spectra were measured in the frequency range from 20 Hz to 2 MHz using a capacitor measurement cell. Investigations have been performed to find the optimal equivalent electric circuits describing the transformation of the electrical properties of cement paste and the interface phenomena occurring in the near-electrode layer of the measurement cell in dependence of the hardening time. It is found that the equivalent circuit parameters are sensitive to different stages of cement paste hardening. A relationship between the spectra of electrical parameters and the processes of cement stone hardening is demonstrated. [ABSTRACT FROM AUTHOR]

Fractional calculus is a mathematical framework that has attracted considerable interest from mathematicians, physicists, and engineers. Among its applications, the use of fractional calculus in the automatic control field has led to interesting results, such as more robust controllers, compared to their integer-order counterparts. The proposed work utilizes the physical realization of a solid-state fractional-order capacitor for the implementation of a fractional-order lead compensator. The proposed capacitor is realized using a carbon black-based dielectric. Therefore, a fully analog closed-loop system implementation is realized. A suitable case study is conducted to validate the controller performance, both from simulations and experimentally. The obtained results further confirm the possibility of realizing and applying a fully analog fractional-order controller. • A realization of a fractional order capacitor is used to realize a Fractional Order Compensator. • The proposed capacitor is realized by using a Carbon-Black-based dielectric. • A fully analog closed loop system implementation is therefore realized. • Results are validated with both simulations and experiments. • The isodamping property has verified. [ABSTRACT FROM AUTHOR]

In an ordinary time-varying capacitor, there is debate on whether a time-domain multiplication or a time-domain convolution of capacitance and voltage determines charge. The objective of this work is to resolve this question by experiments on a time-varying capacitor in parallel with a resistor. It was implemented by a motor-driven potentiometer and op-amps. The response matched a power-law function over about two decades of time, and not an exponential, for several sets of parameters. This confirms the time-domain multiplication model. This result is the opposite of that obtained for a constant phase element (CPE) in its common time- and frequency-varying capacitor interpretation. This demonstrates that a CPE is fundamentally different from an ordinary time- and frequency-varying capacitor.

The paper investigates the impacts of the selected electrical equivalent circuit model, measurement setup, and surrounding environment on the trustworthiness of electrical bioimpedance measurement and obtained model data in the human body. The influence of these constitutive components of the system on finding the model parameters is analyzed and illustrated with examples. The results based on experimental measurements on a forearm near the wrist are provided by employing the model, measurement setup, and novel 16-bit compact wireless impedance analyzer (CIA) according to the outcome of the analysis. The area near the wrist is of interest because of attempts to get cardiac-activity-related impedance changes. It is concluded that a two-electrode system with voltage excitation suits better for determining bioimpedance model parameters in the β dispersion area. The results obtained with the CIA and two capacitive bracelet electrodes on a left forearm were used for the fitting model parameters. Despite the small dimensions of 60 × 60 × 25 mm of the CIA reducing stray capacitance to 8 pF, it provides relative impedance magnitude measurement error below 0.3% and phase error below 0.2 ° in the 10 MHz range. Analysis of the model parameters allowed separation of the electrodes, skin, and internal tissue spectra and revealed the relative significance of model components at different frequencies. [ABSTRACT FROM AUTHOR]

A resistance R s in series with a constant phase element (CPE) of frequency-dependent impedance given by the power law function Z c (s) = 1 / (C α s α) is commonly used for the analysis of steady-state frequency response data exhibiting non-purely capacitive behavior. This is the case in most (bio)(electro)chemical systems including dielectrics, batteries, supercapacitors, capacitive deionization units, biological tissues and bioelectrodes. Passing to the time domain, the current, voltage and charge of the system are governed by differential equations with non-integer, fractional-order operators. The purpose of this study is to provide the exact analytical expressions for the electrical response of an R s -CPE model under linear sweep voltammetry with the use of the Laplace transform method. The electrical variables are expressed in terms of special functions regularly encountered with fractional calculus such as the Fox's H -function and the Mittag-Leffler function, and can be used for modeling non-ideal devices as well as extracting their characteristic parameters. • Exact expressions for the electrical response of non-ideal capacitors to linear voltage excitation. • Charge-voltage relationship is nonlinear in non-ideal capacitors. • Capacitance is non-constant, and follows a power law of time. [ABSTRACT FROM AUTHOR]

Abstract Background Lead is a nonessential heavy metal, which can inhibit heme synthesis and has significant cytotoxic effects. Nevertheless, its effect on the electrical properties of red blood cells (RBCs) remains unclear. Consequently, this study aimed to investigate the electrical properties and the electrophysiological mechanism of lead exposure in mouse blood using Electrical Impedance Spectroscopy (EIS) in 0.01–100 MHz frequency range. Data characteristic of the impedance spectrum, Bodes plot, Nyquist plot and Nichols plot, and Constant Phase Element (CPE) equivalent circuit model were used to explicitly analyze the differences in amplitude–frequency, phase–frequency, and the frequency characteristics of blood in electrical impedance properties. Results Compared with the healthy blood in control mice, the changes in blood exposed to lead were as follows: (i) the hematocrit decreased; (ii) the amplitude–frequency and phase–frequency characteristics of electrical impedance decreased; (iii) the characteristic frequencies (f 0) were significantly increased; (iv) the electrical impedance of plasma, erythrocyte membrane, and hemoglobin decreased, while the conductivity increased. (v) The pseudo-capacitance of cell membrane (CPE_Tm) and the intracellular pseudo-capacitance (CPE-Ti) were decreased. Conclusions Therefore, EIS can be used as an effective method to monitor blood and RBC abnormalities caused by lead exposure. The electrical properties of the cells can be applied as an important observation in the evaluation of the toxic effects of heavy metals.

One of the main challenges during the integration of a carbon/polymer-based nanocomposite sensor on textile substrates is the fabrication of a homogeneous surface of the nanocomposite-based thin films, which play a major role in the reproducibility of the sensor. Characterizations are therefore required in every fabrication step to control the quality of the material preparation, deposition, and curing. As a result, microcharacterization methods are more suitable for laboratory investigations, and electrical methods can be easily implemented for in situ characterization within the manufacturing process. In this paper, several textile-based pressure sensors are fabricated at an optimized concentration of 0.3 wt.% of multiwalledcarbon nanotubes (MWCNTs) composite material in PDMS. We propose to use impedance spectroscopy for the characterization of both of the resistive behavior and capacitive behavior of the sensor at several frequencies and under different loads from 50 g to 500 g. The impedance spectra are fitted to a model composed of a resistance in series with a parallel combination of resistance and a constant phase element (CPE). The results show that the printing parameters strongly influence the impedance behavior under different loads. The deviation of the model parameter α of the CPE from the value 1 is strongly dependent on the nonhomogeneity of the sensor. Based on an impedance spectrum measurement followed by parameter extraction, the parameter α can be determined to realize a novel method for homogeneity characterization and in-line quality control of textile-integrated wearable sensors during the manufacturing process. [ABSTRACT FROM AUTHOR]

InN/InGaN quantum dots (QDs) are found to establish a nonlinear constant phase element (CPE) response over a wide frequency range, measured by electrochemical impedance spectroscopy (EIS). The intrinsic surface donors together with the near-surface electron accumulation layer form the fractional capacitor. The magnitude of the impedance and the phase angle depend on the QD structural parameters and contact area. Importantly, they consistently change with applied voltage, constituting the nonlinear CPE response. A noise-filtering DC voltmeter with the phase angle as readout is proposed. [ABSTRACT FROM AUTHOR]

Objective. Producing realistic numerical models of neurostimulation electrodes in contact with the electrolyte and tissue, for use in time-domain finite element method simulations while maintaining a reasonable computational burden remains a challenge. We aim to provide a straightforward experimental-theoretical hybrid approach for common electrode materials (Ti, TiN, ITO, Au, Pt, IrOx) that are relevant to the research field of bioelectronics, along with all the information necessary to replicate our approach in arbitrary geometry for real-life experimental applications. Approach. We used electrochemical impedance spectroscopy (EIS) to extract the electrode parameters in the AC regime under different DC biases. The pulsed electrode response was obtained by fast amperometry (FA) to optimize and verify the previously obtained electrode parameters in a COMSOL Multiphysics model. For optimization of the electrode parameters a constant phase element (CPE) needed to be implemented in time-domain. Main results. We find that the parameters obtained by EIS can be used to accurately simulate pulsed response only close to the electrode open circuit potential, while at other potentials we give corrections to the obtained parameters, based on FA measurements. We also find that for many electrodes (Au, TiN, Pt, and IrOx), it is important to implement a distributed CPE rather than an ideal capacitor for estimating the electrode double-layer capacitance. We outline and provide examples for the novel time-domain implementation of the CPE for finite element method simulations in COMSOL Multiphysics. Significance. An overview of electrode parameters for some common electrode materials can be a valuable and useful tool in numerical bioelectronics models. A provided FEM implementation model can be readily adapted to arbitrary electrode geometries and used for various applications. Finally, the presented methodology for parametrization of electrode materials can be used for any materials of interest which were not covered by this work., (Creative Commons Attribution license.)

Electrical energy storage devices exhibit dispersive properties that control their charge and discharge processes. To get a deeper understanding of these anomalous phenomena, it is essential to go beyond static viewpoints of circuit theory in order to accurately characterize the complex interplay of internal mechanisms. Specifically, the (dis)charging time of resistive-capacitive networks is commonly estimated as four times the product of the Thévenin resistance and the capacitance itself by assuming ideal exponential relaxations in spite of the intrinsic fractional dynamics of the real energy storage materials, leading to inaccurate and erroneous characterization protocols. The purpose of this work is to provide recommended practices to find the steady-state operation of such type of devices from time-domain data with a decelerated behavior of the Mittag-Leffler function at long time scales, introducing the concept of "incremental capacitance" in the transition from ideal to fractional-order capacitor and thus, an estimation of the charge/discharge time delay. Our theoretical analysis is validated by providing a representative example of experimental application, based on an electrochemical power source, such as supercapacitors under switching-type operation. We hope to bring such study to the attention of multidisciplinary readers, both from academia and industry, focused on energy storage device research. • Steady-state analysis of the fractional-order capacitor. • Concept of "incremental capacitance" in the transition from C to CPE. • Charge/discharge time depends strongly on the dispersive exponent. • Experimental study of supercapacitors using the theory proposed. [ABSTRACT FROM AUTHOR]

A simple single parameter adjustable immittance concept designed with modular active devices, fabricated in I3T $25~0.35~\mu \text{m}$ 3.3 V CMOS process of ON Semiconductor, is introduced. The proposed devices employ an integer-order capacitor and specifically designed fractional-order capacitors (sometimes called constant phase elements). The proposed active topology consists of two simple active elements, namely a linearly voltage adjustable operational transconductance amplifier and a voltage differencing unity gain voltage follower/buffer, and only two passive elements, i.e. redundancy is minimized. The designed topology offers generation of an adjustable immittance having both the capacitive and inductive character. The importance of the order as well as the value of the pseudo-capacitance for design and analyzes are shown, including all important parasitic features for estimation of expected operational bandwidth which have to be considered in the design. The operational bandwidth is determined by high values of approximants of fractional-order capacities (225, 56 and $8.8~\mu \text{F}$ /sec^1- $\alpha $ , where $\alpha $ represents the order equal to 0.25, 0.5 and 0.75, respectively). These parameters result into ranges between tens of Hz and units-tens of kHz. The adjustability of the transconductance from 70 to $700~\mu \text{S}$ by the driving voltage between 0.05 and 0.5 V offers approximately one decade change of equivalent capacitance and inductance. Laboratory-based experiments done with a fabricated prototype confirmed the theoretical presumptions.

The discovery of ferroelectricity in hafnium zirconium oxide (HZO) thin films has attracted wide attention from academia to industry due to the application in ferroelectric non-volatile random access memories (FeRAM) with prominent performance in scalability and CMOS process compatibility. Dielectric behavior of ferroelectric HZO thin films is a key factor affecting the dynamic effect, piezoelectric and electrostrictive effect. Interface between HZO and capping electrodes plays an important role in regulating the dielectric properties. In this paper, the impedance frequency response and dielectric spectrum of ferroelectric HZO thin films were analyzed. Parameters of the interface were extracted to analyze the regulating effect on the dielectric properties based on an impedance model with constant phase element (CPE). Besides, dielectric spectrums at elevated temperatures were identified to verify this analysis.

Interface engineering has become one of the most important research strategies to harness the full potential of perovskite solar cells. Photovoltaic community seems to herald the imminent development of 30% efficient perovskite devices with competitive lifetimes, subject, among other aspects, to clarify "what happens under the interfaces." One of the most powerful techniques to characterize the intermixing ionic‐electronic processes that take place at perovskite interfaces is the Impedance Spectroscopy. It is a real fact that this methodology reveals the characteristic phenomenology attributed to interfacial phenomena, in form of complex spectra that interfere with a proper identification of dominant mechanisms. This article presents approaches to characterizing the non‐ideal electrical properties associated with the appearance of an interfacial capacitance distribution, identifying major sources of intrinsic/extrinsic origin and so, providing further progress in the understanding of phenomenological mechanisms of photovoltaic perovskites. Importantly, the study addresses the evolution of dispersive capacitance's characteristic parameters with light intensity (and bulk thickness), obtaining a useful alternative way of determining the ideality factor and thus, the recombination of charge carriers. The results are discussed in light of critical importance exhibited by the interactions between ionic and electronic species, with the aim of advancing in device efficiency and stability. [ABSTRACT FROM AUTHOR]

The Cole-Cole model for a dielectric is a generalization of the Debye relaxation model. The most familiar form is in the frequency domain and this manifests itself in a frequency dependent impedance. Dielectrics may also be characterized in the time domain by means of the current and charge responses to a voltage step, called response and relaxation functions respectively. For the Debye model they are both exponentials while in the Cole-Cole model they are expressed by a generalization of the exponential, the Mittag-Leffler function. Its asymptotes are just as interesting and correspond to the Curie-von Schweidler current response which is known from real-life capacitors and the Kohlrausch stretched exponential charge response.

Background: Lead is a nonessential heavy metal, which can inhibit heme synthesis and has significant cytotoxic effects. Nevertheless, its effect on the electrical properties of red blood cells (RBCs) remains unclear. Consequently, this study aimed to investigate the electrical properties and the electrophysiological mechanism of lead exposure in mouse blood using Electrical Impedance Spectroscopy (EIS) in 0.01-100 MHz frequency range. Data characteristic of the impedance spectrum, Bodes plot, Nyquist plot and Nichols plot, and Constant Phase Element (CPE) equivalent circuit model were used to explicitly analyze the differences in amplitude-frequency, phase-frequency, and the frequency characteristics of blood in electrical impedance properties.Results: Compared with the healthy blood in control mice, the changes in blood exposed to lead were as follows: (i) the hematocrit decreased; (ii) the amplitude-frequency and phase-frequency characteristics of electrical impedance decreased; (iii) the characteristic frequencies (f0) were significantly increased; (iv) the electrical impedance of plasma, erythrocyte membrane, and hemoglobin decreased, while the conductivity increased. (v) The pseudo-capacitance of cell membrane (CPE_Tm) and the intracellular pseudo-capacitance (CPE-Ti) were decreased.Conclusions: Therefore, EIS can be used as an effective method to monitor blood and RBC abnormalities caused by lead exposure. The electrical properties of the cells can be applied as an important observation in the evaluation of the toxic effects of heavy metals. [ABSTRACT FROM AUTHOR]

This paper presents a state-of-the-art survey in the area of fractional-order element passive emulators adopted in circuits and systems. An overview of the different approximations used to estimate the passive element values by means of rational functions is also discussed. A short comparison table highlights the significance of recent methodologies and their potential for further research. Moreover, the pros and cons in emulation of FOEs are analyzed.

One of the main challenges during the integration of a carbon/polymer-based nanocomposite sensor on textile substrates is the fabrication of a homogeneous surface of the nanocomposite-based thin films, which play a major role in the reproducibility of the sensor. Characterizations are therefore required in every fabrication step to control the quality of the material preparation, deposition, and curing. As a result, microcharacterization methods are more suitable for laboratory investigations, and electrical methods can be easily implemented for in situ characterization within the manufacturing process. In this paper, several textile-based pressure sensors are fabricated at an optimized concentration of 0.3 wt.% of multiwalledcarbon nanotubes (MWCNTs) composite material in PDMS. We propose to use impedance spectroscopy for the characterization of both of the resistive behavior and capacitive behavior of the sensor at several frequencies and under different loads from 50 g to 500 g. The impedance spectra are fitted to a model composed of a resistance in series with a parallel combination of resistance and a constant phase element (CPE). The results show that the printing parameters strongly influence the impedance behavior under different loads. The deviation of the model parameter α of the CPE from the value 1 is strongly dependent on the nonhomogeneity of the sensor. Based on an impedance spectrum measurement followed by parameter extraction, the parameter α can be determined to realize a novel method for homogeneity characterization and in-line quality control of textile-integrated wearable sensors during the manufacturing process.

Polycrystalline Na 0. 9 Ba 0. 1 Nb 0. 9 ( Sn 0. 5 Ti 0. 5 ) 0. 1 O3 is prepared by the solid-state reaction technique. The formation of single-phase material was confirmed by an X-ray diffraction study and it was found to be a tetragonal phase at room temperature. Nyquist plots ( Z ′ ′ versus Z ′) show that the conductivity behavior is accurately represented by an equivalent circuit model which consists of a parallel combination of bulk resistance and constant phase elements (CPE). The frequency dependence of the conductivity is interpreted in terms of Jonscher's law. The conductivity σ d c follows the Arrhenius relation. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (KWW), φ (t) = exp(− (t / τ) β) function and the value of the stretched exponent (β) is found to be almost independent of temperature. The near value of activation energies obtained from the analyses of modulus and conductivity data confirms that the transport is through an ion hopping mechanism dominated by the motion of the ( O 2 −) ions in the structure of the investigated material. [ABSTRACT FROM AUTHOR]

The effect of the thickness of ceramic membrane on the productivity of microbial fuel cells (MFCs) was investigated with respect to the electricity generation and domestic wastewater treatment efficiencies. The thickest ceramic membrane (9 mm) gained the highest coulombic efficiency (27.58±4.2 %), voltage (681.15±33.1 mV), and current and power densities (447.11±21.37 mA/m2, 63.82±10.42 mW/m2) compared to the 6- and 3-mm thick separators. The results of electrochemical impedance spectroscopy (EIS) analysis were investigated to identify the internal resistance constituents by proposing the appropriate equivalent electrical circuit. The Gerischer element was modeled as the coupled reaction, and diffusion in the porous carbon electrodes and the constant phase element was assimilated into the electrical double-layer capacitance. The thickest ceramic (9 mm) was found to have the largest ohmic resistance; however, owing to its superior barrier capability, it provided more anoxic conditions for better accommodation of exoelectrogenic bacteria in the anode chamber. Therefore, lower charge transfer, fewer diffusional impedances, and higher rates of anodic reactions were achieved. Excessive oxygen and substrate crossover through the thinner ceramics (of 6 and 3 mm) resulted in the suppressed development of anaerobic anodic biofilm and the accomplishment of aerobic substrate respiration without electricity generation.

This study proposes a new approach for the optimization of phase and magnitude responses of fractional-order capacitive and inductive elements based on the mixed integer-order genetic algorithm (GA), over a bandwidth of four-decade, and operating up to 1 GHz with a low phase error of approximately ±1°. It provides a phase optimization in the desired bandwidth with minimal branch number and avoids the use of negative component values, and any complex mathematical analysis. Standardized, IEC 60063 compliant commercially available passive component values are used; hence, no correction on passive elements is required. To the best knowledge of the authors, this approach is proposed for the first time in the literature. As validation, we present numerical simulations using MATLAB® and experimental measurement results, in particular, the Foster-II and Valsa structures with five branches for precise and/or high-frequency applications. Indeed, the results demonstrate excellent performance and significant improvements over the Oustaloup approximation, the Valsa recursive algorithm, and the continued fraction expansion and the adaptability of the GA-based design with five different types of distributed RC/RL network.

Electrochemical impedance spectroscopy is finding increasing use in electrochemical sensors and biosensors, both in their characterisation, including during successive phases of sensor construction, and in application as a quantitative determination technique. Much of the published work continues to make little use of all the information that can be furnished by full physical modelling and analysis of the impedance spectra, and thus does not throw more than a superficial light on the processes occurring. Analysis is often restricted to estimating values of charge transfer resistances without interpretation and ignoring other electrical equivalent circuit components. In this article, the important basics of electrochemical impedance for electrochemical sensors and biosensors are presented, focussing on the necessary electrical circuit elements. This is followed by examples of its use in characterisation and in electroanalytical applications, at the same time demonstrating how fuller use can be made of the information obtained from complete modelling and analysis of the data in the spectra, the values of the circuit components and their physical meaning. The future outlook for electrochemical impedance in the sensing field is discussed.

A class of fractal-chain fractance approximation circuit (FCFAC) has been discussed in this paper. The FCFAC type 1 (FCFAC-1) can achieve the rational approximation of negative-half-order fractances. Changing the series and parallel connections or the positions of resistors and capacitors in FCFAC-1 produces another three FCFACs of negative-half-order. Making scaling extensions to the four original FCFACs, the scaling FCFACs can be obtained and achieve the rational approximation of fractances of arbitrary-order. The operational order, which is determined by the progression ratio of resistance α and the progression ratio of capacitance β , can be expressed as μ = − lg α / lg (α β). The approximation performance of the scaling FCFACs has been improved and the optimised circuits are really simple. The oscillation phenomena of the frequency-domain characteristics of the scaling FCFACs have been described quantitatively. In addition, a comparison of approximation performance shows the scaling FCFACs provide a good choice in available fractance approximation circuits (FACs). [ABSTRACT FROM AUTHOR]

Presented work focuses on methods for the extended electronic control in the designs of inductance simulators based on single-loop feedback topology. Implementation is based on diamond transistors as voltage-to-current converters and two voltage-mode multipliers connected to different positions in topology (providing amplification or control of equivalent resistance). Presented solutions achieve significantly extended adjustability of equivalent inductance value in comparison to standard approaches based on CMOS differential pair-based operational transconductances amplifiers. Proposed designs of synthetic inductors are based on utilization of integer-order as well as fractional-order (constant phase element) capacitor. Their features are verified both via PSpice simulations and experimental measurements. Results confirmed intended purposes of designs implementing discussed methods. DOI: http://dx.doi.org/10.5755/j01.eie.24.3.20976

A selection of electrodes was analysed using cyclic-voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and a large apparent resistance was observed with CV that was absent with EIS. The explanation for this resistance anomaly was traced to the constant phase element (CPE) behaviour which is exhibited by the electrode double-layer capacitance. Computer simulations of the transient-response of an RQ network (where Q represents a CPE) to a voltage ramp revealed bi-exponential behaviour, with two separate time-constants. One is equal to the product of R and Q, but the other is fixed at about 0.3 s. This finding is supported by observation, by mathematical derivation, and by a novel mixed-domain five-component equivalent circuit model. In addition, example code is provided as a basis for transient simulations of constant phase elements with arbitrary voltage waveforms. This explanation assists in the correct interpretation of potentially misleading cyclic voltammetry results. Image 1 • Apparent high resistance of cyclic voltammetry due to constant phase element. • Curve-fitting electrical equivalent circuit to cyclic voltammetry waveforms. • Transient simulation of constant phase elements with arbitrary voltage waveforms. [ABSTRACT FROM AUTHOR]

Fractional-order calculus has been used for generalizing many modern and classical control theories including the well establish PID paradigm. The obtained controllers, of non-integer order, must be approximated with high order integer ones, in order to be realized. Successively, analog or digital implementations are used for the real world applications. This approach offers the hip to a classical criticism to fractional calculus. Why design a fractional-order system, which is usually of low order, if you need a high order system to implement it? In order to face this problem, in this paper, a fractional-order capacitor, more specifically a Constant Phase Device, is applied for implementing a first order fractional transfer function. Due to the intrinsic nature of the realized device, just one capacitor is needed for the implementation, avoiding therefore the need of high order RC approximation. Furthermore a fractional-order Wien oscillator and a chaotic Duffing circuit are presented confirming the potentiality of the proposed device in realizing fractional order circuits. [ABSTRACT FROM AUTHOR]

This paper presents a state-of-the-art survey in the area of fractional-order element passive emulators adopted in circuits and systems. An overview of the different approximations used to estimate the passive element values by means of rational functions is also discussed. A short comparison table highlights the significance of recent methodologies and their potential for further research. Moreover, the pros and cons in emulation of FOEs are analyzed. [ABSTRACT FROM AUTHOR]

A novel scheme suitable for the emulation of fractional-order capacitors and inductors of any order less than 2 is presented in this work. Classically, fractional-order impedances are characterized in the frequency domain by a fractional-order Laplacian of the form s ± α with an order 0 < α < 1 . The ideal inductor and capacitor correspond, respectively, to setting α = ± 1 . In the range 1 < α < 2 , fractional-order impedances can still be obtained before turning into a Frequency- Dependent Negative Resistor (FDNR) at α = ± 2 . Here, we propose an electronically tunable fractional-order impedance emulator with adjustable order in the full range 0 < α < 2 . The values of the emulated capacitance/inductance, as well as the bandwidth of operation, are also electronically adjustable. The post- layout simulation results confirm the correct operation of the proposed circuits. [ABSTRACT FROM AUTHOR]

This paper targets on the design and analysis of specific types of transfer functions obtained by the summing operation of integer-order and fractional-order two-port responses. Various operations provided by fractional-order, two-terminal devices have been studied recently. However, this topic needs to be further studied, and the topologies need to be analyzed in order to extend the state of the art. The studied topology utilizes the passive solution of a constant-phase element (with order equal to 0.5) implemented by parallel resistor–capacitor circuit (RC) sections operating as a fractional-order two-port. The integer-order part is implemented by operational amplifier-based lossless integrators and differentiators in branches with electronically adjustable gain, useful for time constant tuning. Four possible cases of the fractional-order and integer-order two-port interconnections are analyzed analytically, by PSpice simulations and also experimentally in the frequency range between 10 Hz and 1 MHz. Standard discrete active components are used in this design for laboratory verification. Practical recommendations for construction and also particular solutions overcoming possible issues with instability and DC offsets are also given. Experimental and simulated results are in good agreement with theory. [ABSTRACT FROM AUTHOR]

Featured Application: The proposed constant phase elements are very accurate over audio frequency bandwidth and can be directly utilized in popular and emerging research discipline: design of fractional-order analog building blocks. This review paper introduces real-valued two-terminal fully passive RC ladder structures of the so-called constant phase elements (CPEs). These lumped electronic circuits can be understood as two-terminal elements described by fractional-order (FO) dynamics, i.e., current–voltage relation described by non-integer-order integration or derivation. Since CPEs that behave almost ideally are still not available as off-the-shelf components, the correct behavior must be approximated in the frequency domain and is valid only in the predefined operational frequency interval. In this study, an audio frequency range starting with 20 Hz and ending with 20 kHz has been chosen. CPEs are designed and values tabularized for predefined phase shifts that are commonly used in practice. If constructed carefully, a maximum phase error less than 0.5° can be achieved. Several examples of direct utilization of designed CPEs in signal processing applications are provided. [ABSTRACT FROM AUTHOR]

An animal model of deep brain stimulation (DBS) was used in in vivo studies of the encapsulation process of custom-made platinum/iridium microelectrodes in the subthalamic nucleus of hemiparkinsonian rats via electrical impedance spectroscopy. Two electrode types with 100-μm bared tips were used: i) a unipolar electrode with a 200-μm diameter and a subcutaneous gold wire counter electrode and ii) a bipolar electrode with two parallelshifted 125-μm wires. Miniaturized current-controlled pulse generators (130 Hz, 200 μA, 60 μs) enabled chronic DBS of the freely moving animals. A phenomenological electrical model enabled recalculation of the resistivity of the wound tissue around the electrodes from daily in vivo recordings of the electrode impedance over two weeks. In contrast to the commonly used 1 kHz impedance, the resistivity is independent of frequency, electrode properties, and current density. It represents the ionic DC properties of the tissue. Significant resistivity changes were detected with a characteristic decrease at approximately the 2nd day after implantation. The maximum resistivity was reached before electrical stimulation was initiated on the 8th day, which resulted in a decrease in resistivity. Compared with the unipolar electrodes, the bipolar electrodes exhibited an increased sensitivity for the tissue resistivity.