Impedance-based Techniques Research Articles

Guest Editorial: Special Issue on Power Electronics and Systems: Modeling, Analysis, Control, and Stability

Recent advances in power electronics have enabled rapid development of applications in power systems, including renewable energy generation, high-voltage dc (HVdc) transmission, flexible ac transmission system, energy storage, and microgrids. Power electronics are also the foundation for new mobile power system technologies, such as variable-frequency ac distribution for more-electric aircraft and medium-voltage dc grids for electric ships. While there has been a steady growth in the use of power electronics on the load side over the last three decades, the penetration of power electronics into the generation, transmission, and distribution areas has far more impacts on system operation, control, and stability. New control interactions and resonance problems have been encountered in renewable energy and HVdc systems, which caught many utility companies, power electronics manufacturers, and operators of wind or PV parks by surprise. New modeling, analysis, and control technologies as well as system stability theories have to be developed. Impedance-based and other frequency-domain techniques are emerging for stability analysis and control of ac power electronics systems. Real-time and hardware-in-the-loop simulation is also becoming common tools for the design and integration of HVdc, renewable energy integration, and microgrid systems.

Robust real-time cell analysis method for determining viral infectious titers during development of a viral vaccine production process

The classical cell-culture methods, such as cell culture infectious dose 50% (CCID50) assays, are time-consuming, end-point assays currently used during the development of a viral vaccine production process to measure viral infectious titers. However, they are not suitable for handling the large number of tests required for high-throughput and large-scale screening analyses. Impedance-based bio-sensing techniques used in real-time cell analysis (RTCA) to assess cell layer biological status in vitro, provide real-time data. In this proof-of-concept study, we assessed the correlation between the results from CCID50 and RTCA assays and compared time and costs using monovalent and tetravalent chimeric yellow fever dengue (CYD) vaccine strains. For the RTCA assay, Vero cells were infected with the CYD sample and real-time impedance was recorded, using the dimensionless cell index (CI). The CI peaked just after infection and decreased as the viral cytopathic effect occurred in a dose-dependent manner. The time to the median CI (CITmed) was correlated with viral titers determined by CCID50 over a range of about 4–5log10 CCID50/ml. This in-house RTCA virus-titration assay was shown to be a robust method for determining real-time viral infectious titers, and could be an alternative to the classical CCID50 assay during the development of viral vaccine production process.

Unlocking Insights into Battery Systems: A Data Science Approach to Impedance Analysis

Developing next generation battery systems requires new insights into how complex materials interact to provide the performance characteristics demanded by tomorrow’s energy storage applications. Electrochemical impedance spectroscopy (EIS) provides a tool for noninvasively probing these systems to uncover a signature of the underlying physicochemical processes. In particular, EIS measurements are useful for characterizing material properties1, studying degradation pathways2, and providing feedback for material design and optimization3. Typically, experimental impedance spectra are related to the underlying physics of the system by fitting an equivalent circuit analog. These models are comprised of any number of electrical circuit elements and make fitting the data to extract system properties relatively straightforward; however, the lumped parameters and degenerate nature of these circuit analogs can limit the available information in complex systems.4 While extensions to EIS, such as nonlinear EIS, can increase the informational content of impedance diagnostics by increasing the sensitivity to different physical parameters and interactions,5,6 taking full advantage of impedance-based techniques ultimately requires moving beyond simply fitting equivalent circuit analogs. For lithium-ion batteries, several rigorous physics-based models have laid the groundwork for a more sophisticated analysis of the impedance response.7,8Here we build on this work to analyze impedance spectra by leveraging insights from the pseudo 2-dimentonal (P2D) battery model. Using a large dataset of simulated impedance spectra for combinations of parameters across a physically meaningful space, the physics-based model can be fit to experimental spectra in a similar method to equivalent circuits (Fig. 1). This data driven approach enables a more robust fitting than trying to optimize the model directly and allows the sensitivity of each parameter to be explored around the fit. Finally, we show that this method is easy to use and invite you to use our open-source, web-based impedance analysis tool to visualize, fit, and interpret your own impedance data!

Enzymatic Detection of Traumatic Brain Injury Related Biomarkers.

Electrochemical detection methods have been popular in the medical diagnostics field. Several well-known devices such as the self-monitoring blood glucose meter have relied on electrochemical techniques for their sensitivity, and ability to make direct measurements without optical labels. Currently, no point-of-care or handheld diagnostic tool exists to quantify the severity of a traumatic brain injury (TBI). We have shown that enzymatic detection of norepinephrine (NE), a biomarker which can indicate TBI severity, using impedance-based electrochemical techniques can achieve the required sensitivity, ∼100pg/mL. Furthermore, the first steps have been taken to quantify NE in whole blood solutions and to optimize the technique for a handheld device.

The self-assembly of redox active peptides: Synthesis and electrochemical capacitive behavior.

The present work reports on the synthesis of a redox-tagged peptide with self-assembling capability aiming applications in electrochemically active capacitive surfaces (associated with the presence of the redox centers) generally useful in electroanalytical applications. Peptide containing ferrocene (fc) molecular (redox) group (Ac-Cys-Ile-Ile-Lys(fc)-Ile-Ile-COOH) was thus synthesized by solid phase peptide synthesis (SPPS). To obtain the electrochemically active capacitive interface, the side chain of the cysteine was covalently bound to the gold electrode (sulfur group) and the side chain of Lys was used to attach the ferrocene in the peptide chain. After obtaining the purified redox-tagged peptide, the self-assembly and redox capability was characterized by cyclic voltammetry (CV) and electrochemical impedance-based capacitance spectroscopy techniques. The obtained results confirmed that the redox-tagged peptide was successfully attached by forming an electroactive self-assembled monolayer onto gold electrode. The design of redox active self-assembly ferrocene-tagged peptide is predictably useful in the development of biosensor devices precisely to detect, in a label-free platform, those biomarkers of clinical relevance. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 357-367, 2016.

Traveling Wave-Based Fault Location on Half-Wavelength Transmission Lines

Transmission lines little longer than half-wavelength have been studied as an alternative for power transmission over very long distances. Recent studies about fault location procedures have proved that most impedance-based techniques are not able to correctly identify the fault point in this kind of line. In this paper, the performance of a two-terminal traveling wave-based fault location approach applied to a transmission line little longer than half-wavelength is investigated through simulations in the Alternative Transients Program (ATP), from which several fault scenarios in a 1000 kV AC line 2600 km long are analyzed. The obtained results indicate traveling wave-based approaches are robust to the atypical operation features of half-wavelength power transmission lines, being suitable for fault location applications in this kind of line.

Impedance analysis of GPCR-mediated changes in endothelial barrier function: overview and fundamental considerations for stable and reproducible measurements.

The past 20 years has seen significant growth in using impedance-based assays to understand the molecular underpinning of endothelial and epithelial barrier function in response to physiological agonists and pharmacological and toxicological compounds. Most studies on barrier function use G protein-coupled receptor (GPCR) agonists which couple to fast and transient changes in barrier properties. The power of impedance-based techniques such as electric cell-substrate impedance sensing (ECIS) resides in its ability to detect minute changes in cell layer integrity label-free and in real-time ranging from seconds to days. We provide a comprehensive overview of the biophysical principles, applications, and recent developments in impedance-based methodologies. Despite extensive application of impedance analysis in endothelial barrier research, little attention has been paid to data analysis and critical experimental variables, which are both essential for signal stability and reproducibility. We describe the rationale behind common ECIS data presentation and interpretation and illustrate practical guidelines to improve signal intensity by adapting technical parameters such as electrode layout, monitoring frequency, or parameter (resistance versus impedance magnitude). Moreover, we discuss the impact of experimental parameters, including cell source, liquid handling, and agonist preparation on signal intensity and kinetics. Our discussions are supported by experimental data obtained from human microvascular endothelial cells challenged with three GPCR agonists, thrombin, histamine, and sphingosine-1-phosphate.

송전선로의 고장점 검출방법에 관한 연구

Most faults that occur on transmission lines are caused by extreme weather with lightning storms in the distance. These are not only prolongs the time of removing and recovering, but also increases economical damages. If faults can be precisely located, maintenance crews can reach them quickly, and remove the faults in time. So, the precise locating of the faulted point on a transmission line is very important to improve the system reliability, and decreases economic damages as an inherent consequence of long term outages. Also, fault location methods are becoming of much importance for utilities and research. In this paper, two single-terminal impedance-based fault location techniques will be investigated to show the reliability and evaluated the performance of reactance and Takagi method by using MATHCAD program simulations.

Visualization of Oxygen Consumption of Single Living Cells by Scanning Electrochemical Microscopy: The Influence of the Faradaic Tip Reaction

The respiration activity of an individual living cell is an indicator of its metabolic vitality. Closely positioned microelectrodes have been suggested for determination of the respiration activity by monitoring the local oxygen concentration. Although first attempts for visualization of the oxygen consumption rate of single living cells by means of scanning electrochemical microscopy (SECM) were already described in 1998, evaluation of the respiratory activity of individual cells remains challenging and the complexity is often underestimated. In particular, the dimensions of the cell itself lead to limitations of conventionally used constant-height mode SECM investigations. Apart from convolution of the oxygen reduction current at the SECM tip with topographic effects, constant-height mode experiments require working distances comparable or below the height of the cell body, thus increasing the risk of tip crash. Attempts to overcome these restrictions include among others positioning of the tip to distances outside the feedback range, embedding of the cells into cavities, or efforts to subtract topographic contributions after cell death. Moreover, as living cells are irregular in dimension, the tip-to-cell distance varies with the tip position. Therefore, constant-distance mode (cd-mode) SECM techniques are inherently advantageous for this purpose. In particular, coupling SECM with scanning probe techniques, such as atomic force microscopy (AFM) and scanning ion conductance microscopy (SICM) as well as shearforce and impedance-based techniques, led to efficient strategies to control the tip-to-sample separation. Recently, we described a shearforce-based cd method (4D SF/ CD-SECM) that is able to work at various tip-to-sample separations. It can hence detect complete diffusion profiles in the surroundings of sources or sinks of redox-active species. Although SECM distance control systems are available, the detection of the respiration activity of single living cells remains challenging. Owing to the small rate of oxygen consumption by a single cell, only small current variations ontop of a high background current are measured. Even more importantly, a biological cell acts as an immiscible liquid– liquid interface in a SECM experiment. Lipophilic redox mediators are known to undergo transmembrane diffusion processes and can be utilized to investigate intracellular redox activity. However, concentration changes in the vicinity of the cellular membrane, for example by the tip reaction, may induce local concentration gradients and cause a diffusional exchange of redox species over the lipid bilayer in a socalled SECM-induced transfer (SECM-IT) mode. The high solubility of oxygen in lipids promotes this transmembrane diffusion and oxygen can easily cross the cell membrane. This diffusion process superimposes the detection of cell respiration. As a result, in most reports addressing detection of cell metabolism based on the detection of variations in the local oxygen concentration, the positioned microelectrode does not act as a passive observer but actively influences the oxygen concentration inside the gap between tip and cell, resulting in imaging artifacts that have not previously been addressed. Even though mentioned occasionally, this effect was neglected in SECM investigations of respiration activity at living cells. Herein, we address the influence of the oxygen reduction rate at the SECM tip on imaging the respiration activity at living cells. We provide strategies to avoid limitations resulting from a strong tip reaction using a potential pulse profile at the tip with a time dependent data acquisition in the shearforce-based cd-mode of SECM. Commonly, the detection of the local oxygen concentration in close proximity to the cell body is performed by means of a variation of the generator-collector mode of SECM with the tip being continuously polarized at oxygen reduction potential. The tip competes with the respiring living cell for the available oxygen inside the gap between SECM tip and cell surface. Crossing the cell body during a SECM line scan should therefore lead to a decrease of the tip current owing to a locally lowered oxygen concentration caused by cell [*] Dr. M. Nebel, S. Gr tzke, Prof. Dr. W. Schuhmann Lehrstuhl f r Analytische Chemie, Elektroanalytik & Sensorik and Center for Electrochemical Sciences, CES Ruhr-Universit t Bochum Universit tsstrasse 150, 44780 Bochum (Germany) E-mail: wolfgang.schuhmann@rub.de

Analysis of the estimation error in a parsimonious temperature-temperature characterization technique

Characterization of systems often relies on a single point response that is a convolution product between a transfer function, an impedance, and the strength of a source. This requires perfect knowledge or measurement of this source. Another possibility is to measure two point responses in such systems. These are also linked, under certain causality conditions, by a different convolution product based on another type of transfer function, called here a transmittance. It is shown that using this kind of transmittance-based model, with one of the two responses as a pseudo-source to explain the other one, leads to a model with fewer parameters, which is very interesting for parameter estimation. Replacement of the exact strength of the source by a noised response in a non-linear least square minimization process does not bring any additional bias and the standard deviations of the parameter estimates can be calculated on a theoretical stochastic basis. An example of such an estimation technique in a thermal characterization of a light insulating sample by the three-layer method is used to show the practical interest of this estimation method and to validate the assessment of the estimation errors through a Monte Carlo approach. Finally a counting of the number of parameters present in the transmittance model, within a very general context of a one-dimension heat transfer characterization experiment, shows its parsimonious character when compared with impedance-based parameter estimation techniques.

From Cellular Cultures to Cellular Spheroids: Is Impedance Spectroscopy a Viable Tool for Monitoring Multicellular Spheroid (MCS) Drug Models?

The use of 3-D multicellular spheroid (MCS) models is increasingly being accepted as a viable means to study cell-cell, cell-matrix and cell-drug interactions. Behavioral differences between traditional monolayer (2-D) cell cultures and more recent 3-D MCS confirm that 3-D MCS more closely model the in vivo environment. However, analyzing the effect of pharmaceutical agents on both monolayer cultures and MCS is very time intensive. This paper reviews the use of electrical impedance spectroscopy (EIS), a label-free whole cell assay technique, as a tool for automated screening of cell drug interactions in MCS models for biologically/physiologically relevant events over long periods of time. EIS calculates the impedance of a sample by applying an AC current through a range of frequencies and measuring the resulting voltage. This review will introduce techniques used in impedance-based analysis of 2-D systems; highlight recently developed impedance-based techniques for analyzing 3-D cell cultures; and discuss applications of 3-D culture impedance monitoring systems.

A Novel Approach for Fault Location of Overhead Transmission Line With Noncontact Magnetic-Field Measurement

Prompt and accurate location of faults in a large- scale transmission system can accelerate system restoration, reduce outage time, and improve system reliability. Traditional approaches are categorized into traveling-wave-based and impedance-based measurement techniques. The traveling-wave-based approach requires detection devices to connect to the high-voltage transmission line, making the solution complex and costly. And the impedance-measurement-based approach is highly dependent on the quality of the signal and affected by fault resistance, ground resistance and non-homogeneity in line configuration. Hence, these approaches may cause a location error that is unacceptable in certain operation cases. In this paper, a novel approach based on noncontact magnetic-field measurement is proposed. With the magnetic field measured along the transmission line by using highly sensitive, broadband, and a low-cost magnetoresistive magnetic sensor, the fault span can be located. The collected data can be further used for identifying the fault type and location within the fault span. The overall system was designed and numerical simulations were performed on typical tower configurations. The simulated results verify the validity of the proposed scheme.

Reference-free impedance-based crack detection in plates

Impedance-based damage detection techniques gained popularity among structural health monitoring (SHM) and nondestructive testing (NDT) communities due to their sensitivity to local damage and applicability to complex structures. In general, conventional impedance-based techniques identify damage by comparing “current” impedance signals with “baseline” ones obtained from the pristine condition of a structure. However, in-situ structures are often subject to changing temperature and loading conditions that can adversely affect measured impedance signals and cause false-alarms. In this paper, a “reference-free” impedance method, which does not require direct comparison of the current impedance signals with the previously obtained baseline impedance signals, is developed for crack detection in a plate-like structure. The proposed technique utilizes a single pair of PZTs collocated on the opposite surfaces of a structure to extract mode conversion produced by crack formation. Then, a reference-free damage classifier is developed and performed on the extracted mode conversion for instantaneous damage diagnosis. Numerical simulations and experimental tests have been conducted explicitly considering varying temperature and loading conditions to demonstrate the robustness of the proposed damage detection technique under varying operational and environmental conditions.

Adaptive Protection of Parallel Transmission Lines Using Combined Cross-Differential and Impedance-Based Techniques

This paper introduces a state-diagram-based protective algorithm for parallel circuit transmission lines using local information obtained at the relay bus. A new cross-differential technique is proposed which compares the currents in the corresponding phases of the parallel circuits in a 2-D space. A companion impedance-based algorithm is used to cover the evolving faults and some conditions in which the cross-differential technique is not able to discriminate the internal faults alone. The effect of the mutual coupling between parallel circuits on the measured impedances is adaptively compensated according to the status of the parallel circuit currents in the segmented 2-D space. The proposed state-diagram-based algorithm combines the outputs of the cross-differential and impedance-based techniques to provide a reliable response under all of the operating statuses of the parallel circuits. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach provides very reliable protection for the double-circuit transmission lines. It covers intercircuit and evolving faults, and is able to reliably select the faulted phases.

Bestimmung der komplexen elektrischen Leitfähigkeit biologischen Gewebes mittels kontaktloser Magnetimpedanzmessung / Estimation of biological tissue conductivity with contact-free magnetic impedance measurements

At present, there are several methods that utilize electrical conductivity of biological tissue, such as biological impedance spectroscopy (BIS). Because these techniques use conductivity values for further analysis (e.g., body water distribution, etc.), accuracy of conductivity measurement is crucial. Traditionally, most impedance-based techniques rely on conductive interaction between tissue and external electrical measurement devices. Thus, electrode properties can influence the results of conductivity measurements. In this study, a contact-free measurement technique is presented, which is based on magnetic induction of eddy currents and measurement of the tiny reinduced voltages in external measurement coils. Our results indicate that it is principally possible to determine conductivity of biological tissue with this technique.

A New Impedance Measurement System for PZT-Based Structural Health Monitoring

Recent research has shown that electromechanical (E/M) impedance-based techniques are an efficient strategy for damage sensing in the context of structural health monitoring (SHM). The basic principle is to excite the lead zirconate titanate (PZT) sensors attached to the structure and to measure the corresponding electrical impedance. A variation in the electrical impedance indicates a variation in the mechanical impedance and, consequently, structural damage. To measure the electrical impedance, most universities and research centers use expensive, bulky, heavy, and high-powered impedance analyzers, which limit new developments and practical applications. To overcome these issues, this paper presents an efficient and inexpensive methodology for electrical impedance measurement. To verify the efficiency and accuracy of the new methodology, practical tests were carried out, and the results were compared with those obtained using a conventional impedance analyzer.

Dielectric screening of early differentiation patterns in mesenchymal stem cells induced by steroid hormones

In the framework of this study, target identification and localization of differentiation patterns by means of dielectric spectroscopy is presented. Here, a primary pre-osteoblastic bone marrow-derived MBA-15 cellular system was used to study the variations in the dielectric properties of mesenchymal stem cells while exposed to differentiation regulators. Using the fundamentals of mixed dielectric theories combined with finite numerical tools, the permittivity spectra of MBA-15 cell suspensions have been uniquely analyzed after being activated by steroid hormones to express osteogenic phenotypes. Following the spectral analysis, significant variations were revealed in the dielectric properties of the activated cells in comparison to the untreated populations. Based on the differentiation patterns of MBA-15, the electrical modifications were found to be highly correlated with the activation of specific cellular mechanisms which directly react to the hormonal inductions. In addition, by describing the dielectric dispersion in terms of transfer functions, it is shown that the spectral perturbations are well adapted to variations in the electrical characteristics of the cells. The reported findings vastly emphasize the tight correlation between the cellular and electrical state of the differentiated cells. It therefore emphasizes the vast abilities of impedance-based techniques as potential screening tools for stem cell analysis.

Reference-free crack detection using transfer impedances

A new concept of reference-free damage detection methodology is developed using transfer impedances to detect crack damage in a plate-like structure without using previously collected baseline data. Conventional impedance-based damage detection techniques have been shown to be vulnerable to other types of changes such as temperature variation that may not be relevant to defects of interest. One of the potential disadvantages of the conventional techniques is frequent false-alarms due to these undesirable variations that may occur in field applications. In order to reduce these false-alarms, this paper proposes a new methodology that utilizes transfer impedances obtained between two pairs of collocated PZT patches instead of the electromechanical impedance obtained at one PZT patch. The proposed technique utilizes Lamb mode conversion effects caused by the presence of crack damage in plate structures. Furthermore, an instantaneous damage classification is carried out by comparing mode conversion energy among several combinations of measured signals without any user-specified threshold or relying on the baseline data. The feasibility of the proposed reference-free methodology using transfer impedances is investigated via a series of experiments conducted on an aluminum plate.