Impedance Magnitude Research Articles

Effects of Aging Treatment on Corrosion Behavior of a Tensile Deformed Al-Cu-Mn-Fe-Zr Alloy in 3.5% NaCl Solution.

In this paper, the effects of an aging treatment on the corrosion resistance/mechanism of a tensile deformed Al-Cu-Mn-Fe-Zr alloy are investigated. The impedance magnitude and polarization resistance increase, while the corrosion current decreases with the increased aging time and temperature. The discontinuously-distributed precipitates and precipitation-free zone, which can cut the corrosion channels, appear at grain boundaries when the temperature is relatively high and the aging time is relatively long. They can improve the corrosion resistance. Additionally, the intergranular and pitting corrosion are the main mechanisms. The intergranular corrosion is likely to occur in an under-aged alloy. This is because the potential difference between the grain boundaries and grains is high, due to the segregation of Cu atoms. When the aging degree is increased, the grain boundary precipitates reduce the potential difference, and the intragranular precipitates make the surrounding matrix prone to dissolution. As such, the pitting corrosion is likely to occur in the over-aged alloys.

STUDY OF THE INFLUENCE OF DISTANCE RELAY SETTING ON AIR LINE HIGH VOLTAGE 150 KV AGAINST HVCRC WIRE 1x310 mm² and ACCC 1x310 mm²

The faults Overhead line is generally caused by short circuit, overload, lightning surge, and tree. Distance relay is one of the protection equipments over the overhead line, and as the main protection by measuring fault impedance magnitude and comparing it to intended impedance. Distance relay setting has wide working area ranging from zone-1, zone-2, and zone-3. The setting must be adjusted when the equipment replacement exists. The replacement of overhead line conductor wire of ACSR 1 x 240 mm² into HVCRC 1 x 310 mm² and ACCC 1 x 310 mm² causing the necessity of re-setting adjustment in purpose of obtaining the appropriate one. This thesis is done by quantitative method which needs parameters in term of number. According to the calculation, the setting is obtained that zone-1 = 41,29257 Ω by t1 = instantaneous, zone-2 = 58,82457 Ω by t2 = 0,8 second, and zone-3 = 69,34377 Ω by t3 = 1,6 second.

Mechanics of Total Drum Replacement Tympanoplasty Studied With Wideband Acoustic Immittance.

Poor hearing outcomes often persist following total drum replacement tympanoplasty. To understand the mechanics of the reconstructed eardrum, we measured wideband acoustic immittance and compared the mechanical characteristics of fascia-grafted ears with the normal tympanic membrane. Prospective comparison study. Tertiary care center. Patients who underwent uncomplicated total drum replacement with temporalis fascia grafts were identified. Ears with healed grafts, an aerated middle ear, and no other conductive abnormalities were included. All patients underwent pre- and postoperative audiometry. Wideband acoustic immittance was measured with absorbance and impedance computed. Fascia-grafted ears were compared with normal unoperated ears. Eleven fascia-grafted ears without complications were included. Postoperatively, the median air-bone gap was 15 dB (250-4000 Hz), with variation across frequency and between ears. Fifty-six control ears were included. Absorbance of fascia-grafted ears was significantly lower than that of normal ears at 1 to 4 kHz (P < .05) but similar below 1 kHz. Impedance magnitude demonstrated deeper and sharper resonant notches in fascia-grafted ears than normal ears (P < .05), suggesting lower mechanical resistance of the fascia graft. The mechanics of fascia-grafted ears differ from the normal tympanic membrane by having lower absorbance at mid- to high frequencies and thus poor sound transmission. The lower resistance in fascia-grafted ears may be due to poor coupling of the graft to the malleus. To improve sound transmission, grafts for tympanic membrane reconstructions would benefit from refined mechanical properties.

Differential contribution of the subthreshold operating currents IT, Ih, and IKir to the resonance of thalamocortical neurons.

Membrane potential oscillations of thalamocortical (TC) neurons are believed to be involved in the generation and maintenance of brain rhythms that underlie global physiological and pathological brain states. These membrane potential oscillations depend on the synaptic interactions of TC neurons and their intrinsic electrical properties. These oscillations may be also shaped by increased output responses at a preferred frequency, known as intrinsic neuronal resonance. Here, we combine electrophysiological recordings in mouse brain slices, modern pharmacological tools, dynamic clamp, and computational modeling to study the ionic mechanisms that generate and modulate TC neuron resonance. We confirm findings of pioneering studies showing that most TC neurons display resonance that results from the interaction of the slow inactivation of the low-threshold calcium current IT with the passive properties of the membrane. We also show that the hyperpolarization-activated cationic current Ih is not involved in the generation of resonance; instead it plays a minor role in the stabilization of TC neuron impedance magnitude due to its large contribution to the steady conductance. More importantly, we also demonstrate that TC neuron resonance is amplified by the inward rectifier potassium current IKir by a mechanism that hinges on its strong voltage-dependent inward rectification (i.e., a negative slope conductance region). Accumulating evidence indicate that the ion channels that control the oscillatory behavior of TC neurons participate in pathophysiological processes. Results presented here points to IKir as a new potential target for therapeutic intervention.NEW & NOTEWORTHY Our study expands the repertoire of ionic mechanisms known to be involved in the generation and control of resonance and provides the first experimental proof of previous theoretical predictions on resonance amplification mediated by regenerative hyperpolarizing currents. In thalamocortical neurons, we confirmed that the calcium current IT generates resonance, determined that the large steady conductance of the cationic current Ih curtails resonance, and demonstrated that the inward rectifier potassium current IKir amplifies resonance.

Semimicroscopic Theory for Underscreening-Induced Anomalous Migration–Diffusion Coupling

We develop a novel theory for the impedance response of reversible electron transfer reactions under the influence of migration–diffusion coupling. Theory accounts for the influence of the supporting electrolyte, electroactive species, solvent, metal, and the interfacial electric field accounting underscreening. This semimicroscopic formalism is based on a modified electrode surface boundary constraint, which circumvents the essential nonlinearity in the Nernst–Planck equation. The interfacial electric field determines the kinetics of formation of compact electric double layer (C-EDL) embedded with electroactive species and influence the mass transport. This kinetics is governed by an intrinsic C-EDL formation resistance (RH), solution resistance (RΩ), and the extent of ion packing dependent on electrolyte composition. Theory unravels a characteristic ohmic-migration frequency, ω* = D/LMΩ2, a prerequisite for the outer sphere electron transfer step. A dimensionless migration–diffusion coupling number δM is unriddled, which quantifies the extent of migration contribution dependent on the potentials at IHP (ϕ1), OHP (ϕ2), diffuse layer (ϕDL), ion size-corrected screening length, charge on electroactive species, interfacial diffusivity, and RH. The magnitude of impedance (in low-frequency regime) evinces an anomalous nonmonotonic variation with ionic strength. Finally, theory accredits us to understand the underscreening-induced anomalies in migration–diffusion-controlled impedance response.

Development of Cu/F-MWCNT/ZnO Based Active Layer for Long Term Soil Urea Measurements

There is a significant interest in the detection of nutrient levels in smart agriculture farms. In this paper, we report the development of Zinc oxide (ZnO) modified multi-walled Carbon nanotube (F-MWCNT) nanocomposite thin film layers specifically for soil nitrogenous fertilizers level detection. The nanostructured ZnO loaded over the surface of F-MWCNT forms the nanocomposite active layer. The surface morphology of the F-MWCNT/ZnO is characterized using field emission scanning electron microscopy (FeSEM) and energy-dispersive X-ray spectroscopy (EDS). Crystal phase and orientation of F-MWCNT, ZnO and F-MWCNT/ZnO nanocomposites were examined using an X-ray diffractometer (XRD). The electrochemical sensing characteristics of the Cu/F-MWCNT/ZnO structure was measured using an impedance/gain phase analyzing system and resulting composite structure was found to have a proportional impedance change with soil Urea levels. The performance of the sensor was investigated in the 1- 10 kHz range. The impedance magnitude was found to be a linearly decrease with the Urea levels.

Theory for influence of uncompensated solution resistance on EIS of diffusion limited adsorption at rough electrode

Theory is developed for the electrochemical impedance spectroscopy (EIS) of the diffusion-limited adsorption process coupled with reversible charge transfer at rough electrodes under the influence of ubiquitous uncompensated solution resistance. This study quantitatively relates the impedance response of rough electrode to its phenomenological components, viz., diffusion limited adsorption, reversible charge transfer and uncompensated solution resistance. The random roughness of electrode is expressed by the surface statistical property, i.e., power spectrum of roughness. The fractal nature of roughness is characterized in terms of fractal dimension, lower cut-off length and topothesy length. The high-frequency regime is controlled by the uncompensated solution resistance whereas the low-frequency regime is governed by the adsorption process. The magnitude of impedance as well as phase decreases with rise in adsorption isotherm (length) parameter. The intermediate frequency regime is controlled by the coupling of adsorption and uncompensated solution resistance with the diffusion process. The fractal roughness parameters has quantitative influence on the magnitude of impedance over whole frequency regime while the phase plot shows qualitative difference in the intermediate frequency regime. The governing length scales which controls the characteristic crossover frequencies are: diffusion length, adsorption-ohmic coupling length and topothesy length (or width of interface). The three emergent crossover frequencies are: (i) ohmic reduced inner crossover frequency (ii) adsorption roughness topothesy dependent pseudo-quasireversibility characteristic frequency (iii) outer crossover frequency. Synopsis: This study quantitatively relates the impedance response of rough electrode to its phenomenological components, viz., diffusion limited adsorption, reversible charge transfer and uncompensated solution resistance. The random roughness of electrode is expressed by the surface statistical property, i.e., power spectrum of roughness.

Analysis and Mitigation of Low-Frequency Interactions Between the Source and Load Virtual Synchronous Machine in an Islanded Microgrid

Source-side virtual synchronous machines (VSGs) and load-side VSMs (LVSM) are gradually utilized together in the microgrid to provide virtual inertia and damping. However, instability occurs in the islanded microgrid system due to the interaction dynamics between the VSG and the LVSM, which has been investigated in this article. At first, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -frame impedance models of the VSG and the LVSM are established and compared. It is revealed that the d-d channel impedance of LVSM behaves the negative resistor with a V-type magnitude in the low-frequency range, which easily interacts with the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–d</i> channel impedance of the VSG and leads to instability of the system. Thus, the inductor current feedforward control and the additional voltage feedback control are proposed for the VSG to reshape its impedance. It diminishes the impedance magnitude and generates the active impedance of the VSG. In this way, the low-frequency interaction between the VSG and the LVSM can be mitigated. Besides, the proposed control preserves the dynamic performance of the system. Finally, simulations and experiments verify the effectiveness of stability analyses and the proposed suppression method.

Facile manufacturing of sub-mm thick CNT-based RC filters

CNT-Based RC networks are described with the purpose of showing empirical findings on the influence of the interdigitated electrodes (IDE) spacing, the dispersant compound and the number of deposited layers, on the impedance magnitude and phase of the CNTs. Additionally, we propose use-cases for these networks, applying them to the realization of filters of second order with easily tunable cut-off frequency, and with the inherent advantages of CNTs and printed technologies, rendering them a prime choice for applications where thin and flexible second order filters are necessary.

Composition-tuned lithium aluminosilicate as a new humidity-sensing ceramic material with high sensitivity

Though numerous types of humidity sensors have been proposed to date, the continuous emergence of new applications requires relentless improvements in sensor performance and a constant pursuit of new sensing materials. Herein, the composition of lithium aluminosilicates (LiAlSi2O6 and Li2Al2SiO6) that slightly absorb H2O molecules is tuned along with the addition of LiCl and Si2N3, in order to maximize the H2O adsorption. The optimal composition is discovered via use of a particle swarm optimization algorithm, which is a population-based metaheuristic approach. After three generations of searching, we finally develop Li2.10Al1.23Si1.54Cl0.05O5.95 (LAS-CNO), which shows the highest value of RRH=43 %/RRH=75 % (R is ionic resistance and RH is the relative humidity). Density-functional-theory calculation also reveals that the presence of Cl− and a vacancy defect on Al/Si sites contribute to preferential H2O adsorption on the (001) surface of LAS-CNO (hexagonal P6222). Accordingly, the magnitude of impedance (│Z│) at 100 Hz significantly varies from 200 MΩ (RH = ca. 0 %) to 1.0 kΩ (RH = 97 %), in contrast to relatively small decreases in │Z│ to 630 and 59 kΩ for LiAlSi2O6 and Li2Al2SiO6, respectively. An almost linear of │Z│ vs. RHs is also observed for RH values ranging between 9 and 97 %. Furthermore, the linearity is not weakened and the values of │Z│ are not significantly altered with measuring-frequencies. Due to strong H2O adsorption on LAS-CNO, hysteresis is noticeable between the adsorption and desorption processes, but other superior properties (sensitivity, stability, and linearity) validate that LAS-CNO could be a new humidity-sensing material.

On the use of the frequency domain in assessing resonant overvoltages during transformer energization.

Resonant temporary overvoltages during transformer energization may result in damage to the transformer itself or surrounding equipment. These overvoltages are caused by the interplay between the transformer energization currents and the grid impedance. Current practice to assess the risk of transformer energization is by classifying grid scenarios into potentially problematic or non-problematic based on the magnitude of the grid impedance at frequencies coinciding with the grid harmonic frequencies. At the moment, this approach lacks a proof of validity. Therefore, this paper investigates the use of frequency domain characteristics, and more in general, linear analysis of the grid impedance, for assessing the risk associated with transformer energization. Findings show that the magnitude of the frequency domain grid impedance may not provide sufficient information for classifying problematic and non-problematic cases.

A 30-MHz, 3-D Imaging, Forward-Looking Miniature Endoscope Based on a 128-Element Relaxor Array.

This work describes the design, fabrication, and characterization of a 128-element crossed electrode array in a miniature endoscopic form factor for real-time 3-D imaging. Crossed electrode arrays address some of the key challenges surrounding probe fabrication for 3-D ultrasound imaging by reducing the number of elements required (2N compared with N2). However, there remain practical challenges in packaging a high-frequency crossed electrode array into an endoscopic form factor. A process has been developed that uses a thinly diced strip of flex circuit to bring the back-side connections to common bond surface, which allows the final size of the endoscope to measure only [Formula: see text] mm. An electrostrictive ceramic composite design was developed for the crossed electrode array. A laser dicing system was used to cut the 1-3 composite as well as etch the array electrode pattern. A single quarter wavelength Parylene matching layer made was vacuum deposited to finish the array. The electrical impedance magnitude of array elements on resonance was measured to be 49 Ω with a phase angle of -55.5°. The finished array elements produced pulses with -6-dB two-way bandwidth of 60% with a 34-MHz center frequency. The average measured electrical crosstalk on the nearest neighboring element and next to nearest neighboring element was -37 and -29 dB, respectively. One- and two-way pulse measurements were completed to confirm the pulse polarity and fast switching speed. Preliminary 3-D images were generated of a wire phantom using the previously described simultaneous azimuth and Fresnel elevation (SAFE) compounding imaging technique.

Spread Spectrum Time Domain Reflectometry and Steepest Descent Inversion Spread Spectrum Time Domain Reflectometry and Steepest Descent Inversion

In this paper, we present a method for estimating complex impedances using reflectometry and a modified steepest descent inversion algorithm. We simulate spread spectrum time domain reflectometry (SSTDR), which can measure complex impedances on energized systems for an experimental setup with resistive and capacitive loads. A parametric function, which includes both a misfit function and stabilizer function, is created. The misfit function is a least squares estimate of how close the model data matches observed data. The stabilizer function prevents the steepest descent algorithm from becoming unstable and diverging. Steepest descent iteratively identifies the model parameters that minimize the parametric function. We validate the algorithm by correctly identifying the model parameters (capacitance and resistance) associated with simulated SSTDR data, with added 3 dB white Gaussian noise. With the stabilizer function, the steepest descent algorithm estimates of the model parameters are bounded within a specified range. The errors for capacitance (220pF to 820pF) and resistance (50 Ω to 270 Ω) are &lt; 10%, corresponding to a complex impedance magnitude |R +1/jωC| of 53 Ω to 510 Ω.

In situ continuously monitoring of cancer cell invasion process based on impedance sensing

Activation of invasion and metastasis is recognized as one of the hallmarks of cancer. There are 90% of cancer-related deaths due to metastasis and given that it is worthy of note to study cancer progression and metastasis. Owing to restricted tools used to underpin the study of tumor invasion process, an on-site platform was developed to monitor this event in vitro. We used interdigital gold electrodes to monitor the dynamic process of cancer cells invading into extracellular matrix in situ continuously. Influences of collagen concentration and number of cancer cells on the measured impedance was exhibited. In addition, the parameters used to demonstrate the experiment results were optimized. The change of impedance magnitude indicated the cell-matrix interaction during invasion process. The potential further use of this platform would be complementary in cell studies when concerning metastasis.

Characterization of stem cell-like property in cancer cells based on single-cell impedance measurement in a microfluidic platform

Investigation of stem cell-like property in cancer cells is important for the development of new therapeutic drugs targeting at malignant tumors. Currently, the standard approach for identifying cancer stem cell-like cells relies on the recognition of stem cell surface markers. However, the reliability remains controversial among biologists. In the current work, a dielectrophoretic and impedimetric hybrid microfluidic platform was developed for capturing single cells and characterizing their stem cell-like property. Single cells were captured in 20 μm trapping wells by dielectrophoretic force and their impedance spectra were measured by an impedance analyzer. The result showed that different cancer cell lines could be differentiated by impedance magnitude ranging between 2 and 20 kHz. Moreover, cancer cells and cancer stem cell-like cells could be categorized by a 2-dimensional graph of the impedance magnitudes at 2 and 20 kHz. The stem cell-like property in cancer cells was verified by stem cell surface markers and single-cell derived colony assay. Comparing with bio-chemical approach, i.e., surface markers, bio-physical approach, i.e., cell impedance, is a label-free technique to identify cancer stem cell-like cells.

High impedance fault detection based on current harmonic analysis using Chirp Z transform

High Impedance Fault (HIF) is a problematic fault of feeders which its fault current is lower as compared to normal current in power system. Likewise, due to magnitude of impedance engaged in fault area and behavior of fault current is specific and not the same as the usual fault current profile which cannot be identified by standard relays. The HIF is created whenever a live conductor contacts with objects owning large impedance. The HIFs Signal has high index of similarity with some normal cases in feeders like Nonlinear loads (NL) waveform, or instant of switching of linear loads (LL), capacitor banks (CB) and full load transformers (FLT), which provided methods must distinguish them. So, the paper utilized a novel method with ability of recognizing HIF from all possible events in feeders with high accuracy. The Chirp Z Transform (CZT) has been applied to extract the features of HIF and/or other usual network events signal. It is possible to appropriately detect fault by low order harmonics of current signal extracted by means of CZT. Maximum discrepancy of detection is nearly 7 ms which is accurate enough. Also, absence of threshold values in algorithm makes it simple and can be used in each type of distribution and even transmission systems. Working in low-frequency harmonics is another advantage of this method because needs lower sampling frequency. The evaluated signals of HIF, NLs, LLs, capacitors and FLT are acquired by a simulated 13.8 kV distribution system in MATLAB/Simulink.

Continuous MOF Membrane-Based Sensors via Functionalization of Interdigitated Electrodes

Three M-MOF-74 (M = Co, Mg, Ni) metal-organic framework (MOF) thin film membranes have been synthesized through a sensor functionalization method for the direct electrical detection of NO2. The two-step surface functionalization procedure on the glass/Pt interdigitated electrodes resulted in a terminal carboxylate group, with both steps confirmed through infrared spectroscopic analysis. This surface functionalization allowed the MOF materials to grow largely in a uniform manner over the surface of the electrode forming a thin film membrane over the Pt sensing electrodes. The growth of each membrane was confirmed through scanning electron microscopy (SEM) and X-ray diffraction analysis. The Ni and Mg MOFs grew as a continuous but non-defect free membrane with overlapping polycrystallites across the glass surface, whereas the Co-MOF-74 grew discontinuously. To demonstrate the use of these MOF membranes as an NO2 gas sensor, Ni-MOF-74 was chosen as it was consistently fabricated as the best thin and homogenous membrane, as confirmed by SEM. The membrane was exposed to 5 ppm NO2 and the impedance magnitude was observed to decrease 123× in 4 h, with a larger change in impedance and a faster response than the bulk material. Importantly, the use of these membranes as a sensor for NO2 does not require them to be defect-free, but solely continuous and overlapping growth.

Evaluation of Medium Voltage Network for Propagation of Supraharmonics Resonance

Power converters with high switching frequency used to integrate renewable power sources to medium and low voltage networks are sources of emission in the supraharmonic range (2 to 150 kHz). When such converters are connected to a medium voltage (MV) network these supraharmonics propagate through the MV network and can impact network and customer equipment over a wide range. This paper evaluates an existing Swedish MV electrical network and studies the pattern of supraharmonic resonance and the propagation of supraharmonics. The MV network consists of eight feeders including a small wind farm. Simulations reveal that, the bigger the MV network, the more resonant frequencies, but also the lower the amplitude of the resonance peaks in the driving point impedance. It was also identified that for short feeders as length increases, the magnitude of the transfer impedance at supraharmonic frequency decreases. For further increment in feeder length, the magnitude increases or becomes almost constant. For very long feeders, the transfer impedance further starts decreasing. The eight feeders in the network under study are similar but show completely different impedance versus frequency characteristics. Measurements at the MV side of the wind farm show time varying emissions in the supraharmonic range during low power production. The impact of these emissions coupled with system resonance is examined.

MIL-88A (Fe) filler with duplicate corrosion inhibitive/barrier effect for epoxy coatings: Electrochemical, molecular simulation, and cathodic delamination studies

The MIL-88A (Fe) as a MOF based on Fe+3 cations and fumaric acid was fabricated as a corrosion inhibitive filler to achieve a protective coating with duplicate active/passive inhibition properties. The polarization test indicated that the MIL-88A (Fe) saline-based extract had an inhibition effect. The formation of an inhibitive layer was seen in the EIS results for the sample immersed in the MIL-88A (Fe) extract. The slight solubility of MIL-88A (Fe) in the water (122.4ppm total organic carbon and 2ppm Fe+3) caused the inhibitive ions' release. The adsorption of release species from MIL-88A (Fe) scaffold on the substrate was confirmed by the theoretical (QM, MC/MD) computations. The EIS and salt spray test results obtained from scratched epoxy coated samples showed the Epoxy-MIL-88A (Fe) coating's active inhibition effect. The pull-off adhesion strength and cathodic delamination resistance were also improved in the presence of MIL-88A (Fe). The adhesion loss of epoxy coatings after 7 days of exposure to the salt spray decreased from 31.4% to 9.4%, respectively. The unscratched samples filled with MIL-88A (Fe) particles showed excellent barrier properties. The breakpoint frequency value declined from 2.4 to 0.8, and the reduction of low-frequency impedance magnitude decreased from 33% to 20%.

Electrochemical behavior of Zn‐REP nanohybrid coatings during marine Shewanella sp. biofilm formation

AbstractNanohybrid coatings, particularly zinc‐rich epoxy coatings, can protect steel from the harsh marine environment through a physical barrier mechanism and a cathodic protective effect based on anodic electrochemical reactions involving zinc particles in the coating. New additives, such as carbon nanotubes (CNTs), produce more efficient multifunctional coatings by enhancing both protective mechanisms. In this study, the electrochemical behavior and corrosion mechanisms of zinc‐rich epoxy nanohybrid coatings with the addition of CNTs were investigated in the presence of a Shewanella sp. marine strain to evaluate their influence on biofilm formation by this Gram‐negative bacterium. The electrochemical activity was monitored over time with open‐circuit potential, electrochemical impedance spectroscopy, and scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy. A mixed mechanism was observed starting from early exposure. When the content of CNTs was doubled, the biofilm adherence improved, thus suggesting a favorable effect of CNTs on biofilm formation, attributable to increased production of bacterial exopolymeric substances facilitating biofilm development. The electrochemical impedance spectroscopy results suggested a correlation with biofilm formation as a second barrier layer with the lowest impedance magnitude in coatings with different multiwalled CNT content.