Steady-state Impedance Research Articles

Response Surface Modeling of the Steady-State Impedance Responses of Gas Sensor Arrays Comprising Functionalized Carbon Nanotubes to Detect Ozone and Nitrogen Dioxide.

Carbon nanotube (CNT) sensors provide a versatile chemical platform for ambient monitoring of ozone (O3) and nitrogen dioxide (NO2), two important airborne pollutants known to cause acute respiratory and cardiovascular health problems. CNTs have shown great potential for use as sensing layers due to their unique properties, including high surface to volume ratio, numerous active sites and crystal facets with high surface reactivity, and high thermal and electrical conductivity. With operational advantages such as compactness, low-power operation, and easy integration with electronics devices, nanotechnology is expected to have a significant impact on portable low-cost environmental sensors. Enhanced sensitivity is feasible by functionalizing the CNTs with polymers, metals, and metal oxides. This paper focuses on the design and performance of a two-element array of O3 and NO2 sensors comprising single-walled CNTs functionalized by covalent modification with organic functional groups. Unlike the conventional chemiresistor in which the change in DC resistance across the sensor terminals is measured, we characterize the sensor array response by measuring both the magnitude and phase of the AC impedance. Multivariate response provides higher degrees of freedom in sensor array data processing. The complex impedance of each sensor is measured at 5 kHz in a controlled gas-flow chamber using gas mixtures with O3 in the 60-120 ppb range and NO2 between 20 and 80 ppb. The measured data reveal response change in the 26-36% range for the O3 sensor and 5-31% for the NO2 sensor. Multivariate optimization is used to fit the laboratory measurements to a response surface mathematical model, from which sensitivity and selectivity are calculated. The ozone sensor exhibits high sensitivity (e.g., 5 to 6 MΩ/ppb for the impedance magnitude) and high selectivity (0.8 to 0.9) for interferent (NO2) levels below 30 ppb. However, the NO2 sensor is not selective.

A new window on subcutaneous ICD system performance: Z-lead impedance change over time in devices with and without extracellular matrix envelope use

Abstract Background Device impedance for subcutaneous ICDs (S-ICDs) may rise over time reflecting changes in tissue electrical conduction due to fibrosis from the natural foreign body response, increasing the risk of defibrillation failure. A biologic envelope optimized for S-ICDs may mitigate fibrosis and encourages angiogenesis around the device possibly decreasing impedance rise over time. The S-ICD system performs routine low-voltage Z-lead (LVZ) impedance testing (impedance between shocking coil and can) that may provide insight into the impedance changes on device functionality and efficacy over time. Purpose Explore early and late impedance changes over time in S-ICDs implanted with and without envelopes using periodic LVZ measurements. Methods 30 patients received S-ICDs (15 with envelope) between 1/2017 and 3/2021, after excluding those with device complications, uncontrolled comorbidities, or recent cardiac surgery. Impedance data was recorded at initial implantation. LVZ impedance data was extracted from the wireless remote monitoring system, trended over 0–4 years post implant, and analyzed blinded to patient information. Results 24 patients (12 envelope) had evaluable implant and chronic data sets. Baseline clinical characteristics were similar between groups. Impedance in general was higher in the envelope group at initial implantation (LVZ mean 89 Ω vs 74 Ω) and throughout the first year. Comparing envelope to no envelope, the initial average shock impedance was 87.3±30.50 vs 66.7±10.40, followed by an average low-V impedance drop of 29 Ω vs 17 Ω during the first month, with a recovery to 109 Ω vs 91 Ω at 30 months post implant. After 30 months, impedance trends demonstrated a modest linear increase up to 48 months in the no envelope group in comparison with a modest decrease in the envelope group (sample sizes too small to determine significance) (Figure 1). Conclusion The results demonstrate periodic LVZ testing in the S-ICD monitoring system can reliably trend changes in system impedance over time. Impedance measurements within the first 6–7 months (and most markedly within the first 3 months) appear to be transiently lower than the values seen after this timepoint suggesting that early impedance measurements may not predict steady-state impedance. Further studies are needed to explore the impact of envelope use and the S-ICD impedance changes beyond 30 months. Funding Acknowledgement Type of funding sources: None.

Multi-Sine EIS for Early Detection of PEMFC Failure Modes

Electrochemical impedance spectroscopy (EIS) is a powerful technique that can be used to detect small changes in electrochemical systems and subsequently identify the source of the change. While promising, analysis is often non-intuitive and time-consuming, where collection times of a single EIS spectrum can reach several minutes. To circumvent the long collection times associated with traditional EIS measurements, a multi-sine EIS technique was proposed in which the simultaneous application of many frequencies can reduce the acquisition time to less than a minute. This shortened acquisition time opens the possibility to use multi-sine EIS as a real-time diagnostic tool for monitoring the state-of-health of commercial fuel cell systems. In this work, a single-cell proton exchange membrane fuel cell (PEMFC) was characterised using multi-sine EIS, by establishing steady-state impedance response under baseline conditions before systematically changing operating conditions and monitoring the dynamic changes of the impedance response. Our initial results demonstrate that full multi-sine EIS spectra, encompassing a frequency range from 50 kHz to 0.5 Hz, can be collected and analysed using simple equivalent circuit models in 50 s. It is shown that this timeframe is sufficiently short to capture the dynamic response of the fuel cell in response to changing operating conditions, thereby validating the use of multi-sine EIS as a diagnostic technique for in-situ monitoring and fault detection during fuel cell operation.

A Saturated Amorphous Alloy Core-Based Inrush Current Limiter to Eliminate Inrush Currents and Restrain Harmonics during Transformer Energization

In this paper, a new saturated amorphous alloy core-based inrush current limiter (ICL) has been designed and built to limit the inrush current of a power transformer. A toroidal core with a middle limb is developed using the Metglas amorphous alloy and the middle limb is excited with a dc current to saturate the amorphous alloy core. Only a very small dc excitation current is required using such a core when compared to that using a similar design with conventional materials. Under normal conditions, the saturated amorphous alloy ICL core steady-state impedance is low and has a negligible effect on the operation of the system. During the energization of a power transformer connected to the ICL, the large inrush current de-saturates the amorphous alloy core, resulting in an increase in the ac winding impedance, which limits the peak amplitude of the transformer inrush current and harmonics. To validate the proposed saturated amorphous alloy core-based ICL, a prototype ICL has been built and tested in the laboratory. The experimental results show that the core power loss, core saturation, the fundamental and harmonics of the inrush current of the proposed saturated amorphous alloy core-based ICL are significantly better compared with those from the sheet steel core-based ICL. It is expected that the proposed saturated amorphous alloy core will be used in future inrush current limiters that can help to improve the performance of the power transmission and distribution system.

Dynamic electrochemical impedance spectroscopy for the charge transfer rate measurement of the ferro/ferricyanide redox couple on gold

• Rate coefficients of charge transfer are determined by dynamic EIS. • Rate coefficients are presented in a 0.2 V broad range. • By using dEIS, it is easier to preserve cleanliness of the system. • No a priori assumptions on potential dependences of rates are involved. The use of dynamic electrochemical impedance spectroscopy, dEIS is shown in the context of diffusion-controlled electrode reactions. By this method, a number of audio-frequency impedance spectra were measured on a gold electrode in an aqueous solution of K 4 [Fe(CN) 6 ] while taking cyclic voltammograms (the CVs were taken with 50–200 mV/s scan-rate; the distance of potentials of impedance spectra was 16 mV). The Faradaic impedance elements were determined from the spectra, from them charge transfer rate coefficients were calculated; it was found to be 0.11 cm/s at the formal potential. This set of measurements demonstrates the main advantage of dEIS over the traditional steady state impedance measurements: dEIS characterization of an electrochemical system can be performed in seconds rather than minutes which makes possible to use freshly prepared (e.g., annealed) electrodes with reduced risk of contamination or modification of their surfaces.

Evaluation principle and method of horizontal grounding electrode based on time‐varying impedance

The length of the horizontal grounding electrode is usually extended to decrease the impulse grounding resistance. In this paper, the mechanism for influencing the effective length is revealed by studying the dispersal process of a horizontal electrode and a method for determining the length is proposed. Firstly, the impulse current and the response voltage are measured at different positions. The results are used to analyse the time-varying characteristics of the impedance in the dispersal process, the mechanism and the factors influencing the effective length. Furthermore, the current propagation process is divided into a wave head process and a wave tail process. The variation rule and influencing factors of the transient impedance are determined. The wave head impedance acts as a dynamic process from the injection impedance to the wave tail impedance, and the injection impedance is not affected by the length of the grounding electrode. The wave tail impedance is constant and is equal to the DC steady-state impedance. It is proposed that the effective length is caused by two different dispersal processes and it is obtained when the tail impedance is equal to the impulse grounding resistance. These results are highly significant for optimizing the grounding device.

Essential relation of spin states, trap states and photo-induced polarization for efficient charge dissociation in a polymer-nonfullerene based organic photovoltaic system

Organic nonfullerene acceptors (NFA) have received tremendous research interests due to the efficient interfacial charge transfer (CT) when they combine with polymeric donors. It is of critical importance to unravel, to which extent, spin-dependent excited states, energetic disorder and photo-induced polarization are essentially correlated, and eventually contribute for the photovoltaic action. Herein, we explore them in a polymer-NFA ITTC based organic bulk heterojunction (BHJ) solar cell. With assist of magneto-photocurrent measurements at the short-circuit current density (Jsc) condition and steady state impedance spectroscopic measurements, the dominant mechanism for the Jsc generation is governed by the triplet-charge reaction. We postulate that long lived triplets are more likely to interact with trapped charges at excited states, giving rise to Jsc. It turns out that the trap states may not always act as passive role for the energy loss in the organic photovoltaic system. More importantly, both applied bias voltage and light can effectively manipulate the magnitude and sign of the magneto-photocurrent. By quenching the photo-generated build-in field, the bias-dependent magneto-photocurrent evidently proves the efficient dissociation of polaron pairs at CT states. In particular, the photo-excitation wavelength has strong impact on the hyperfine field. Lastly, we demonstrate that the double beam photo-excitation generated dipole-dipole interaction assists for the electron-hole dissociation. Our work may pave the way for understanding the inside spin- and photo-physical phenomena in the NFA based organic photovoltaic system.

A new dynamic interaction factor for the analysis of pile groups subjected to vertical dynamic loads

Τhis paper presents an analytical method for calculating the steady-state impedance factors of pile groups of arbitrary configuration subjected to harmonic vertical loads. The derived solution allows considering the effect of the actual pile geometry on the contribution of pile-soil-pile interaction to the response of the group, via the introduction of a new dynamic interaction factor, defined on the basis of soil resistance instead of pile displacements. The solution is first validated against a published solution for single piles that accounts for the effect of pile geometry on the generated ground vibrations. Accordingly, we show that the derived soil attenuation factor agrees well with existing solutions for pile groups in the high frequency range, but considerable differences are observed in both the stiffness and damping components of the computed impedance when the relative spacing between piles decreases. Numerical results obtained for typical problem parameters suggest that ignoring pile geometry effects while estimating the contribution of pile-soil-pile interaction in the response may lead to inaccurate results, even for relative large pile group spacings.

AC Loss Analysis of a Flux-Coupling Type Superconducting Fault Current Limiter

Fault current limiter (FCL) is commonly applied as a current-limiting device to improve the stability of the power system. A flux-coupling type superconducting FCL (FC-SFCL) which mainly consists of a current-limiting unit has been developed. Because of its low steady-state impedance and larger current-limiting impedance at pre-and post-fault, it is regarded as a possible way to restrict fault currents. In this paper, ac loss performances of three structures with different winding methods under three operations were discussed. Then an experimental platform for a small-scale prototype was set up, and several relevant experiments were implemented to test current reduction capacity and loss levels. In theory, the resistive loss obtained by integrating the instantaneous power corresponds to the ac losses of the current-limiting unit. It provides a feasible way to measure ac losses of a magnet, but it needs further verification.

Effects of Chemical Bath-Deposited TiO2 Compact Layer on the Performance of the Fully Screen-Printable Hole-Transport Material-Free Mesoscopic Perovskite Solar Cells with a Carbon Electrode

The optimization of a compact layer in perovskite solar cells (PSCs) strongly influences the device performance. In this work, we prepared a TiO2 compact layer through simple hydrolysis of aqueous TiCl4 solution and have investigated the influence of the TiO2 compact layer on the performance of the fully screen-printable hole-transport material (HTM)-free PSCs with a carbon electrode. The PSC prepared from the TiO2 compact layer made by hydrolyzing TiCl4 precursor solution for 70 min achieved the highest device performance, with a short-circuit current density of 20.01 mA cm−2, an open-circuit voltage of 0.96 V, a fill factor of 0.60 and a power conversion efficiency of 11.53%. Cyclic voltammetry, steady-state photoluminescence spectroscopy and electrochemical impedance spectroscopy were performed to study the charge transfer process in the device. The obtained results suggest that the compact layer in the solar cell structure without HTM plays a decisive role. The improved device performance was attributed to the increase of the charge transport ability and a charge recombination resistance in the TiO2 compact layer.

Enhancing the fault ride through capability of DFIG‐based wind energy system using saturated core fault current limiter

Doubly fed induction generator (DFIG) is the most popular machine for the wind power application that consists of the ability for variable speed operation and reactive power control with the help of power electronics converters. It is one of the prominent system that follows grid code requirement as it remains connected with the grid even during the fault occurrence. For making the DFIG continuity in the grid, low-voltage ride through or fault ride through (FRT) techniques are used. Fault current limiter is one of the major schemes used under the FRT. A saturated core fault current limiter (SCFCL) is used in DFIG system to enhance the FRT capability. The main property of SCFCL is the change in permeability between the saturated and unsaturated conditions of the magnetic core to concurrently provide low steady-state impedance and high transient fault impedance for limiting the fault current.

High Performance Biosensor Based on Electronic Transduction of Refractive Index Using 3D Nanostructured Biogenic Silica

Various nanostructured materials have been deployed in developing biosensors. Nevertheless, achieving sub-attomolar detection limit by label free method is still challenging owing to the different noises during the sensing process. In this paper, we introduce an impedance immunosensor on freely suspended 3D nanostructured biogenic silica block, commonly called Tabashir. The working principle of this sensor is based on the electrical transduction of variations in refractive index after antigen capture. Due to the variation in refractive index, the Tabashir sensor changes the solution lining on the surface and within the pores, which has been converted to a significant variation in bulk conductivity. This screens the impedance measurement from major noise interference like the surface charge fluctuations and antibody-antigen association dissociation transients, resulting in a remarkable steady state impedance sensitivity of around 120% along with distinct shape and cut-off frequencies in the noise power spectral density (PSD) for a trace concentration of 0.1 aM Hep-B virus even in a complex mixture containing high concentration of non-specific antigen. This detection limit is an improvement by almost two orders of magnitude compared to the most sensitive label free electrical biosensor.

Analysis of Magnetic Circuit and Leakage Magnetic Field of a Saturated Iron-Core Superconducting Fault Current Limiter

The saturated iron-core superconducting fault current limiter (SISFCL) is considered to be an effective solution to reduce the impact of fault current and increase the reliability of the power grid. This paper presents the basic structure and the electromagnetic analysis of SISFCL. In order to study the leakage magnetic flux distribution of the SISFCL, two approaches have been used to model the transient behavior of such device. The leakage magnetic flux distribution of the limiter was calculated, respectively, by using the finite element method (FEM) and the magnetic field division method. By considering the SISFCL as a controlled voltage source dominated by the flux through the ac coils, we establish a magnetic circuit. With the magnetic circuits, we calculate the steady-state impedance. Comparing the results with the FEM model, we verify the validity of the equivalent magnetic circuit model.

Computational Study on the Steady-state Impedance of Saturated-core Superconducting Fault Current Limiter

This paper presents the electromagnetic analysis of a high voltage saturated-core superconducting fault current limiter (SCSFCL). The numerical analyses of a three-dimensional (3D) model is shown, and the specific parameters are given. The model focus on the steady-state impedance of the limiter when connected to the power grid. It analyzed the dependence of steady-state impedance on the AC coil current, and the relationship between oil gap and coil inductance. The results suggest that, adding oil gap between slice of silicon steel can reduce the core cross-section, restrain the ultraharmonic and decrease the steady-state impedance. As the core cross-section of AC limb decreased from 4344 cm2 to 3983 cm2, the total harmonic distortion for voltage decreased from 2.4% to 1.8%, and the impedance decreased from 1.082Ω to 1.069Ω(Idc=400A,Iac=1296A).

The Influence of Temperature of Electrodeposition on the Electrochemical Properties of Ni+MoS<sub>2</sub> Composite Coatings

The Ni+MoS2composite coatings were prepared by electrodeposition under galvanostatic conditions from the Ni-plating bath containing suspended MoS2powder (100 mesh). Investigations of hydrogen evolution reaction (HER) were carried out using steady-state polarization measurements and electrochemical impedance spectroscopy (EIS) in 5 M KOH solution on the coatings obtained at 30, 40, and 50°C. It was found that the kinetics of the HER on the Ni+MoS2coatings decreases with the increase in the electrodeposition temperature of the coatings. This effect is attributed to decreasing content of MoS2(from 26.4 to 18.0 wt.%) embedded into the Ni matrix as composite crystalline component having the electrocatalytic properties towards the HER and/or surface development of the coatings. The higher amount of MoS2was embedded, the more porous electrodes containing pear-shape pores on the surface were produced what was detected by EIS.

Comparison of Electrochemical Properties of Ni+MoS<sub>2</sub> and Ni Coatings in an Alkaline Solution

The Ni+MoS2composite coatings were obtained by electrolytic co-deposition of crystalline nickel with molybdenum sulfide powder from an electrolyte containing suspension of this powder. For comparison, the Ni coating was also deposited. These coatings were obtained in galvanostatic conditions at the current density ofjdep= -250 mA cm-2. A scanning electron microscope was used for surface morphology characterization of the coatings. The behavior of the coatings was investigated in the process of hydrogen evolution reaction from 5 M KOH solution using steady-state polarization and electrochemical impedance spectroscopy methods. It was found that introduction of molybdenum sulfide into nickel matrix, evokes developed and rough surface which is the reason for the increase in the rate of the HER as comapred to the smooth Ni electrode. Thus obtained coatings may be useful in application as electrode materials for the HER.

The Influence of Temperature of Electrodeposition on the Electrochemical Properties of Ni+MoS<sub>2</sub>+Mo Composite Coatings

The Ni+MoS2+Mo composite coatings were obtained by the electrodeposition under the galvanostatic conditions (jdep= -250 mA cm-2) at the temperature of 30-60°C from the nickel bath containing a suspension of MoS2(<2 μm) and Mo (3-7 μm) powders. Studies of hydrogen evolution reaction (HER) were carried out in 5 M KOH solution at room temperature using steady-state polarization and electrochemical impedance spectroscopy (EIS) measurements. The decrease of electrochemical activity towards the HER was found for the Ni+MoS2+Mo composite coatings with the increase in the temperature of their electrodeposition due to decrease of both the intrinsic activity and surface development.

Influence of Surface Development of Ni/W Coatings on the Kinetics of the Electrolytic Hydrogen Evolution

The Ni+W composite coatings were prepared by electrodeposition under the galvanostatic conditions (jdep= -300 mA cm-2) from the nickel plating bath containing an addition of tungsten powder of different granulation (<150 nm, 12 μm, <150 μm). For comparison, the Ni-W alloy coating was also obtained. Studies of hydrogen evolution reaction (HER) were carried out in 5 M KOH solution at room temperature using steady-state polarization and electrochemical impedance spectroscopy (EIS) measurements. It was found that for the Ni+W (<150 μm) composite coating increase in the activity of HER was observed in comparison with the others coatings.

Comparison of Electrochemical Properties of Ni+NiAl and Ni Coatings in an Alkaline Solution

The Ni+NiAl nanocomposite coatings were prepared by the electrodeposition under the galvanostatic conditions (jdep= -250 mA cm-2) from the nickel bath containing the suspension of NiAl nanopowder. For comparison, the Ni coatings were also obtained. The combined steady-state polarization and electrochemical impedance spectroscopy (EIS) investigations of hydrogen evolution reaction (HER) were carried out in 5 M KOH solution at room temperature. It was found that the Ni+NiAl nanocomposite coatings revealed higher apparent electrocataltic activity towards the HER as compared to the comparable Ni deposits due to the increase in the real surface area development and the intrinsic activity.

The Hydrogen Evolution Reaction on Ni Electrode Material Modified with Molybdenum(IV) Oxide and Chromium(III) Oxide Powders

The Ni+MoO2and Ni+Cr2O3composite coatings were prepared by the electrodeposition under the galvanostatic conditions (jdep= -200 mA cm-2) from the nickel bath containing powder of MoO2or Cr2O3. Studies of hydrogen evolution reaction (HER) in 5 M KOH solution at room temperature were conducted using steady-state polarization and electrochemical impedance spectroscopy (EIS) methods. It was ascertained that the HER rate is higher for the Ni+MoO2composite electrode in comparison with the Ni+Cr2O3composite electrode due to the presence of Mo in the nickel matrix.