Frequency-dependent Impedance Research Articles

Significant enhancement in the conductivity of highly transparent PEDOT:PSS thin film through maleic acid treatment

Abstract The conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS, a conducting polymer) thin film is enhanced by simply maleic acid treatment. Here, we have investigated the conductivity enhancement with the variation of maleic acid concentration. The conductivity enhances up to 1.0 M maleic acid concentration and decreases afterward. The optimum conductivity is obtained as 9.35 S cm–1, which is nearly 263 times more compared to the pristine PEDOT:PSS film. The conductivity of the film also depends upon the treating temperature. Therefore, the effect of different treating temperatures on the conductivity enhancement is studied, and the optimum temperature is found to be 140°C. Maleic acid-treated PEDOT:PSS films also exhibit high transmittances, i.e., ≈ 90 – 84 % in the visible region. The mechanism related to the conductivity enhancement and other related information are collected through different spectroscopic and microscopic measurements. Besides, frequency-dependant impedance and electrochemical activity of maleic acid-treated PEDOT:PSS films are also performed. The interaction of maleic acid with PEDOT:PSS promotes the reduction of ionic interaction between PEDOT and PSS chains, resulting in the phase separation between PEDOT and PSS. As a result, the PSS– turn into neutral PSSH and is rinsed away by water, which supports the morphological change and the conductivity enhancement due to the conformational change of coil-like PEDOTs to elongated and better-connected PEDOT chains.

Effective models of metasurface/metainterface made of three-dimensional Helmholtz resonators

We study a reflective metasurface made of 3D subwavelength Helmholtz resonators. We provide an effective model in the time domain obtained by using a three-scale asymptotic approach. The metasurface is reduced to an homogenized boundary condition involving a resonant, frequency dependant impedance. Our effective model takes into account boundary layer effects near the neck opening, and we provide a precise method to calculate the " added length ". The study is extended to meta-interface in transmission, where the set of effective boundary conditions are replaced by effective jump conditions, and the results are discussed in frequency domain with comparison with direct numerical simulations.

Validation of an eigenvalue-based inverse method for estimating locally-reacting surface impedance

Accurate boundary condition descriptions are essential for creating accurate computational models for room acoustics. These descriptions are often defined in terms of absorption coefficients or surface impedances. However, obtaining complex-valued, frequency-dependent values for an acoustically absorbing material sample at low frequencies is a challenging task. In fact, the current measurement standard ISO 354:2003 does not provide a method for measuring absorption coefficients below 100 Hz. In this paper, a recently proposed eigenvalue-based inverse method for estimating locally-reacting impedance at measurement system resonance frequencies is validated. The validation uses data from three samples measured in an impedance tube. The method is also used to estimate complex-valued, frequency-dependent impedances at frequencies below 100 Hz in a measured reverberant room and in a simulated reverberation chamber.

Verification of frequency-dependent impedance boundaries for the Finite-Volume Time-Domain scheme

Numerical simulation methods are widely used to approximate solutions to the wave-equation, taking into account the initial condition ('initial sources') and boundary conditions ('wall materials'). Trustworthy simulations are essential; a primary step is to ensure the correctness of the implementation through a process known as code verification. In this work, we do code verification by studying the convergence of the known finite-volume time-domain (FVTD) method with a frequency-dependent boundary condition modeled as an inductance/resistance/capacitance (LRC) termination. Due to the difficulties of obtaining an analytical solution for frequency-dependent impedance boundaries, we thoroughly derive and implement The Method of Manufactured Solutions tailored to the wave-equation inside a rectangular room for uniform frequency- dependent wall impedance. Asymptotic estimates are found empirically based on a convergence study compared against the manufactured ground truth solution. We investigate the impact of the frequency-dependent boundaries on the convergence affected by the total sum of numerical errors and validate the theoretical properties of the FVTD scheme for various LRC model configurations. The method should also serve as a useful resource for others to verify the correctness of their code implementations.

Towards estimating acoustic surface impedances at low frequencies in a reverberation chamber

To accurately simulate interior acoustical fields, reliable descriptions of the physical properties of the acoustical space are required. While geometry, propagation medium properties, and source characteristics are, in general, easily accessible, the absorption characteristics of the bounding surfaces of a space can be difficult to obtain. For commonly used materials, databases of absorption coefficients could be used. However, absorption coefficient databases are of limited use at low frequencies, especially below 100 Hz. Furthermore, measurement-based estimations tend to be more reliable. Thus, there is incentive to perform measurement-based estimations of the absorption characteristics of a room's bounding surfaces at low frequencies. This work considers the estimation of sound absorption, given in terms of locally-reacting surface impedance, at modal frequencies. This is made feasible by solving an inverse eigenvalue problem. The spatially-uniform, frequency-dependent impedance of the bounding surfaces of a reverberation chamber is estimated. The method is validated by comparing measured transfer functions to simulated transfer functions, which are generated using the estimated impedance. It is shown that the proposed method can be used to estimate locally-reacting surface impedance from measured room impulse responses at low frequencies.

Effects of ZnO additive on the electrical and densification properties of A-site deficient barium cerate perovskite

The dual strategies of A-site deficiency and addition of ZnO sintering aid have been employed to optimise stability and densify the high-temperature proton conductor Ba0.95Ce0.8Y0.2O3-δ at 1200 °C (B95CYZn-1200). Structural analysis performed by Rietveld refinement based on X-ray diffraction data indicated perovskite phase with monoclinic symmetry (space group, I2/m). Raman spectroscopy revealed the presence of ZnO for material sintered at 1200 °C, which most likely partially resides in grain-boundary regions, leading to enhanced electrical transport observed by impedance spectroscopy at low temperature. Anomalous and reproducible frequency-dependent impedance behaviour below 500 °C, observed in various atmospheres, is suggested to be attributable to the varistor-type properties of ZnO. The electrical conductivity of B95CYZn-1200 in the range 500–900 °C is typical of perovskite proton conductors but with greater conductivity than both Ba-stoichiometric BaCe0.8Y0.2O3-δ and ZnO-free Ba0.95Ce0.8Y0.2O3-δ in wet O2 and N2, reaching ∼ 1.1 S m−1 at 550 °C in wet O2. Resistance to carbonate formation and mechanical breakdown was demonstrated via prolonged impedance measurements in CO2- and H2-containing atmospheres in the range 600–700 °C.

Statistical Metamodel of Liner Acoustic Impedance Based on Neural Network and Probabilistic Learning for Small Datasets

The main novelty of this paper consists of presenting a statistical artificial neural network (ANN)-based model for a robust prediction of the frequency-dependent aeroacoustic liner impedance using an aeroacoustic computational model (ACM) dataset of small size. The model, focusing on percentage of open area (POA) and sound pressure level (SPL) at a zero Mach number, takes into account uncertainties using a probabilistic formulation. The main difficulty in training an ANN-based model is the small size of the ACM dataset. The probabilistic learning carried out using the probabilistic learning on manifolds (PLoM) algorithm addresses this difficulty as it allows constructing a very large training dataset from learning the probabilistic model from a small dataset. A prior conditional probability model is presented for the PCA-based statistical reduced representation of the frequency-sampled vector of the log-resistance and reactance. It induces some statistical constraints that are not straightforwardly taken into account when training such an ANN-based model by classical optimizations methods under constraints. A second novelty of this paper consists of presenting an alternate solution that involves using conditional statistics estimated with learned realizations from PLoM. A numerical example is presented.

Electrical transport and dielectric relaxation mechanism in Zn0.5Cd0.5Fe2O4 spinel ferrite: A temperature- and frequency-dependent complex impedance study

In the present study, the frequency-dependent dielectric relaxation and electrical conduction mechanisms in sol-gel-derived Zn0.5Cd0.5Fe2O4 (ZCFO) spinel ferrite were studied in the temperature range of 343–438 K. The formation of the ZCFO spinel ferrite phase with space group Fd3m was confirmed by X-ray diffraction analysis. The dielectric relaxation and electrical conduction mechanisms were studied using complex impedance spectroscopy (CIS). In the Nyquist plots, depressed semicircles were fitted with an equivalent circuit model with configuration (RGBQGB) (RGQG), signifying the contributions from grain boundaries and grains to the charge transport mechanism in the sample. The frequency-dependent AC conductivity was found to follow Jonscher's power law, and the frequency exponent term depicted the overlapping large polaron hopping (OLPH) model as the dominant transport mechanism. The activation energies for conductivity, electric modulus and impedance were calculated to identify the nature of the charge carriers governing the relaxation and conduction mechanisms in the prepared sample. Complex modulus studies confirmed the non-Debye type of dielectric relaxation, whereas tangent loss and dielectric constant analyses confirmed the thermally activated hopping mechanism of charge carriers in Zn0.5Cd0.5Fe2O4 spinel ferrite.

Frequency-Dependent Grounding Impedance of a Pair of Hemispherical Electrodes: Inductive or Capacitive Behavior?

This article is the authors’ last contribution to a trilogy of research papers submitted to Energies’ Special Issue on Electromagnetic Field Computation, aimed at the theoretical analysis and numerical computation of the frequency-dependent complex impedance of hemispherical electrodes. In this work, we consider a pair of distant identical hemispherical electrodes buried in the ground, whose constitutive parameters (conductivity and permittivity) are assigned diverse values. Simulation experiments carried out using a full-wave finite element method, considering different combinations of the earth’s constitutive parameters, reveal that the grounding impedance of the electrode system can exhibit surprisingly varied frequency behavior. For frequencies close to zero, the impedance can start out inductive or capacitive, then go through a number of resonant transitions between inductive and capacitive states, finally tending towards purely resistive behavior. The results are interpreted using theoretical approximations valid for low- and high-frequency regimes.

Exact solution for the electrical response of a constant phase element with a series resistance to linear voltage sweep

A resistance Rs in series with a constant phase element (CPE) of frequency-dependent impedance given by the power law function Zc(s)=1/(Cαsα) 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 Rs-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.

Incident and Load Power Relations in a Mismatched Lossless Transmission Line

In this article, a set of equations is derived to find incident and load power explicitly in terms of load and source reflection coefficients in a lossless transmission line mismatched to both source and load impedances. A transmission line can be mismatched as the frequency varies if the source and load impedances are frequency dependent. Unlike in a scenario, where the transmission line is either matched to the source or load, the incident and load power depends on the length of the transmission line when both the source and load impedances are not matched to the line. The equations derived show that the power varies with the line length with a period of half wavelength. The maximum and minimum incident and load power with the corresponding line lengths are derived. The use of the Smith chart to find these lengths and the ratio of maximum to minimum is also described. Finally, three applications of the results including an additional version of the Friis transmission equation and the bandwidth improvement of power transfer for frequency dependent source and load impedances are presented.

Field tests of square and double exponential pulses for transient resistivity measurements using Wenner arrays and hemispheres

Models of frequency-dependent soil resistivity ρ(f) suggest the dual concept of time-dependent resistivity ρ(t) that, for high resistivity soil, increases from 100 ns to 100 μs, a range of time relevant for lightning backflashover performance calculations. Measurements of ρ(t) can be made by impressing impulse or step current and monitoring voltage rise. Time-dependent resistivity can be established with Wenner or Schlumberger probe arrays and also with oblique fall-of-potential measurements from buried hemispheres. Tests show that rectangular and double-exponential pulse currents both have value. Specialized evaluation using “Drained Net Charge” concepts may yield estimates of low-frequency resistivity ρo.

Impedance-Based Method for Predictive Stability Assessment

Impedance-based analysis methods enable a more specific and earlier foundation for assessing harmonic stability in decentralized converter-based power plants compared to the conventional compliance testing in the grid connection process. Essentially, they can be implemented as black-box model approaches without the necessity to disclose internal control models. Initially, only knowledge of the input impedances of the planned grid connection point and the planned PV system is required for application. For this purpose, the method of impedance spectroscopy for inverters has already been developed as a means to determine the effective impedance profile and the internal harmonic sources of inverters, allowing for the description of the frequency-dependent behavior of individual units. The time- and frequency-dependent grid impedance at the grid connection point (GCP) has also been successfully measured in several campaigns on medium and low-voltage grids. Through the coordinated application of both measurement methods, a predictive harmonic assessment is intended in the future, ensuring high planning reliability and grid quality even in grids with a high penetration of power electronics-coupled systems. This paper provides an overview of the current state of research on impedance-based stability criteria and presents measurement methods for practical implementation. Furthermore, it outlines remaining open questions until application in the field.

LAMA improves tissue oxygenation more than LABA in patients with COPD.

The effect of bronchodilators is mainly assessed with forced expiratory volume in 1 s (FEV1) in chronic obstructive pulmonary disease (COPD). Their impact on oxygenation and lung periphery is less known. Our objective was to compare the action of long-acting β2-agonists (LABA-olodaterol) and muscarinic antagonists (LAMA-tiotropium) on tissue oxygenation in COPD, considering their impact on proximal and peripheral ventilation as well as lung perfusion. FEV1, Helium slope (SHe) from a single-breath washout test (SHe decreases reflecting a peripheral ventilation improvement), frequency dependence of resistance (R5-R19), area under reactance (AX), lung capillary blood volume (Vc) from double diffusion (DLNO/DLCO), and transcutaneous oxygenation (TcO2) were measured before and 2 h post-LABA (day 1) and LAMA (day 3) in 30 patients with COPD (FEV1 54 ± 18% pred; GOLD A 31%/B 48%/E 21%) after 5-7 days of washout, respectively. We found that TcO2 increased more (P = 0.03) after LAMA (11 ± 12% from baseline, P < 001) compared with LABA (4 ± 11%, P = 0.06) despite a lower FEV1 increase (P = 0.03) and similar SHe (P = 0.98), AX (P = 0.63), and R5-R19 decreases (P = 0.37). TcO2 and SHe changes were negatively correlated (r = -0.47, P = 0.01) after LABA, not after LAMA (r = 0.10, P = 0.65). DLNO/DLCO decreased and Vc increased after LAMA (P = 0.04; P = 0.01, respectively) but not after LABA (P = 0.53; P = 0.24). In conclusion, LAMA significantly improved tissue oxygenation in patients with COPD, while only a trend was observed with LABA. The mechanisms involved may differ between both drugs: LABA increased peripheral ventilation, whereas LAMA increased lung capillary blood volume. Should oxygenation differences persist over time, LAMA could arguably become the first therapeutic choice in COPD.NEW & NOTEWORTHY Long-acting muscarinic antagonists (LAMAs) significantly improved tissue oxygenation in patients with COPD, while only a trend was observed with β2-agonists (LABAs). The mechanisms involved may differ between drugs: increased peripheral ventilation for LABA and likely lung capillary blood volume for LAMA. This could argue for LAMA as the first therapeutic choice in COPD.

Impedance of nanocapacitors from molecular simulations to understand the dynamics of confined electrolytes

Nanoelectrochemical devices have become a promising candidate technology across various applications, including sensing and energy storage, and provide new platforms for studying fundamental properties of electrode/electrolyte interfaces. In this work, we employ constant-potential molecular dynamics simulations to investigate the impedance of gold-aqueous electrolyte nanocapacitors, exploiting a recently introduced fluctuation-dissipation relation. In particular, we relate the frequency-dependent impedance of these nanocapacitors to the complex conductivity of the bulk electrolyte in different regimes, and use this connection to design simple but accurate equivalent circuit models. We show that the electrode/electrolyte interfacial contribution is essentially capacitive and that the electrolyte response is bulk-like even when the interelectrode distance is only a few nanometers, provided that the latter is sufficiently large compared to the Debye screening length. We extensively compare our simulation results with spectroscopy experiments and predictions from analytical theories. In contrast to experiments, direct access in simulations to the ionic and solvent contributions to the polarization allows us to highlight their significant and persistent anticorrelation and to investigate the microscopic origin of the timescales observed in the impedance spectrum. This work opens avenues for the molecular interpretation of impedance measurements, and offers valuable contributions for future developments of accurate coarse-grained representations of confined electrolytes.

Non-zero crossing current–voltage characteristics of interface-type resistive switching devices

A number of memristive devices, mainly ReRAMs, have been reported to exhibit a unique non-zero crossing hysteresis attributed to the interplay of resistive and not yet fully understood “capacitive” and “inductive” effects. This work exploits a kinetic simulation model based on a stochastic cloud-in-a-cell method to capture these effects. The model, applied to Au/BiFeO3/Pt/Ti interface-type devices, incorporates vacancy transport and capacitive contributions. The resulting nonlinear response, characterized by hysteresis, is analyzed in detail, providing an in-depth physical understanding of the virtual effects. Capacitive effects are modeled across different layers, revealing their significant role in shaping the non-zero crossing hysteresis behavior. Results from kinetic simulations demonstrate the impact of frequency-dependent impedance on the non-zero crossing phenomenon. This model provides insight into the effects of various device material properties on the non-zero crossing point, such as Schottky barrier height, device area, and oxide layer.

Electrochromic nickel-oxide-based thin films in KOH electrolyte: Ionic and electronic effects elucidated by impedance spectroscopy

Ni-oxide-based thin films, prepared by sputtering, are investigated by electrochemical impedance spectroscopy in a KOH electrolyte. The films are electrochromic, and an increase of the applied potential leads to a variation from a bleached to a colored state as a result of proton (H+) extraction together with extraction of electrons from the valence band. The complex frequency-dependent impedance displays different features in different potential ranges. At low potentials, where coloration is weak, the spectra give evidence for a constant-phase element in parallel with a leak resistance. At intermediate and high potentials, the impedance spectra indicate the presence of a diffusion process, and a model for anomalous diffusion gives excellent fits to the spectra except in a crossover region. The applicability of this model in a significant part of the studied potential range suggests the presence of a multiple-trapping process for the ions. The potential dependence of the chemical capacitance, as well as the diffusion coefficient of un-trapped ions, are analyzed. The electrochemical density-of-states of the charge-compensating electrons gives indications of the top of the valence band and of a band tail extending into the band gap. Diffusion coefficients are found to increase steeply in the crossover potential region to very high values at high potentials. These features are discussed and related to the electrochromic behavior of Ni-oxide-based thin films.

Intra-breath changes in respiratory mechanics are sensitive to history of respiratory illness in preschool children: the SEPAGES cohort

BackgroundIntra-breath oscillometry has been proposed as a sensitive means of detecting airway obstruction in young children. We aimed to assess the impact of early life wheezing and lower respiratory tract illness on lung function, using both standard and intra-breath oscillometry in 3 year old children.MethodsHistory of doctor-diagnosed asthma, wheezing, bronchiolitis and bronchitis and hospitalisation for respiratory problems were assessed by questionnaires in 384 population-based children. Association of respiratory history with standard and intra-breath oscillometry parameters, including resistance at 7 Hz (R7), frequency-dependence of resistance (R7 − 19), reactance at 7 Hz (X7), area of the reactance curve (AX), end-inspiratory and end-expiratory R (ReI, ReE) and X (XeI, XeE), and volume-dependence of resistance (ΔR = ReE-ReI) was estimated by linear regression adjusted on confounders.ResultsAmong the 320 children who accepted the oscillometry test, 281 (88%) performed 3 technically acceptable and reproducible standard oscillometry measurements and 251 children also performed one intra-breath oscillometry measurement. Asthma was associated with higher ReI, ReE, ΔR and R7 and wheezing was associated with higher ΔR. Bronchiolitis was associated with higher R7 and AX and lower XeI and bronchitis with higher ReI. No statistically significant association was observed for hospitalisation.ConclusionsOur findings confirm the good success rate of oscillometry in 3-year-old children and indicate an association between a history of early-life wheezing and lower respiratory tract illness and lower lung function as assessed by both standard and intra-breath oscillometry. Our study supports the relevance of using intra-breath oscillometry parameters as sensitive outcome measures in preschool children in epidemiological cohorts.

Development of ultra-high energy storage density and ultra-wide operating temperature behavior of a lead-free capacitor sensor; (Bi1/2 K1/2) (Fe1/3Mn1/3W1/3)O3

In the present report, attention has been focused on the development of electronic components of a high-energy storage density in small dimensions using ceramic technology and standard techniques. The detailed studies of electrical and dielectric properties of a potassium, manganese, and tungsten modified complex perovskite with a chemical composition: (Bi1/2K1/2) (Fe1/3Mn1/3W1/3)O3 (by solid-state reaction route) have been attempted for the purpose. Through the analysis of structural X-ray diffraction and micro-structural properties, the quality of the developed material has been verified. These methods have provided a crystallite size of 97 nm, and micro-strain (0.0027) and a grain size of 9.83 μm. Studies of frequency and temperature dependent dielectric and complex impedance support the divergence of dielectric dispersion and relaxation from Debye-type behavior. The nature of conductivity of the material of semiconductor type suggests its potential use in optoelectronic component. The temperature coefficient of resistance of −1.3491% confirms that it is a contender for thermistor devices applications. These findings indicate that material with high energy storage density and minimal energy loss could be used for energy storage devices. The dielectric constant and efficiency of 671 and 70.44%, respectively with a maximum power density (0.16 MW/cm3) at 1 kHz is achieved for the devices.

Near-perfect sound absorption using hybrid resonance between subwavelength Helmholtz resonators with non-uniformly partitioned cavities

We present near-perfect sound absorption using a metasurface composed of meta-atoms (MAs) which are subwavelength Helmholtz resonators (HRs) with cavities non-uniformly partitioned by membranes. By embedding the membranes at different horizontal locations in the cavities, we break geometrical symmetry between the MAs so as to derive hybrid resonance between the MAs at our target frequency. The resonance frequency of each MA is determined by delicately adjusting the locations of the membranes, resulting in perfect absorption at the target frequency which is different from the resonance frequencies of MAs. The metasurface is designed to satisfy impedance matching conditions with air at one or more target frequencies with the aid of a theoretical model for frequency-dependent effective acoustic impedance. The theoretical model is established with physical reality by considering the higher-order eigenmodes of the membrane, the visco-thermal losses in narrow orifices, and the end corrections of the subwavelength HR. The designed metasurface is fabricated and its absorption performance is verified experimentally in an impedance tube. Near-perfect absorption of sound is achieved at the target frequency of 500 Hz, which is 12.3% lower than that of near-perfect absorption by previous metasurfaces inducing hybrid resonance between HRs without membranes.