Specific Impedance Research Articles

A Comparative Study on Substituted Polyanilines for Supercapacitors

ABSTRACTThe effect of two substituent groups, ortho-methoxy (-OCH3) and methyl (-CH3) in aniline, have been studied for supercapacitor applications. The polyaniline (PANI), poly (o-anisidine) (POA) and poly (o-toluidine) (POT) have been synthesized by oxidative polymerization method, and characterized by Cyclic Voltammetry (CV), UV–visible spectroscopy, Raman spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques. The specific capacitance, charging/discharging and electrochemical impedance characteristics of the supercapacitor fabricated using PANI, POA, as well as POT electrodes are evaluated in 2M H2SO4 electrolytic media. The highest specific capacitance of 400 F/g is calculated for PANI, whereas, POA and POT have exhibited 360 F/g and 325 F/g capacitance in supercapacitor studies.

The potential of classic and specific bioelectrical impedance vector analysis for the assessment of sarcopenia and sarcopenic obesity.

PurposeThe aim of this paper is to investigate whether bioelectrical impedance vector analysis (BIVA) can be a suitable technique for the assessment of sarcopenia. We also investigate the potential use of specific BIVA as an indicator of sarcopenic obesity.Subjects and methodsThe sample comprised 207 free-living elderly individuals of both sexes, aged 65 to 93 years. Anthropometric and bioelectrical measurements were taken according to standard criteria. The “classic” and “specific” BIVA procedures, which respectively correct bioelectrical values for body height and body geometry, were used. Dual energy X-ray absorptiometry (DXA) was used as the reference method for identifying sarcopenic and obese sarcopenic individuals. Bioelectrical and DXA values were compared using Student’s t-test and Hotelling’s T2 test, as well as Pearson’s correlation coefficient.ResultsAccording to classic BIVA, sarcopenic individuals of both sexes showed higher values of resistance/height (R/H; p < 0.01) and impedance/height (Z/H; p < 0.01), and a lower phase angle (p < 0.01). Similarly, specific BIVA showed significant differences between sarcopenic and nonsarcopenic individuals (men: T2 = 15.7, p < 0.01; women: T2 = 10.7, p < 0.01), with the sarcopenic groups showing a lower specific reactance and phase angle. Phase angle was positively correlated with the skeletal muscle mass index (men: r = 0.52, p < 0.01; women: r = 0.31, p < 0.01). Specific BIVA also recognized bioelectrical differences between sarcopenic and sarcopenic obese men (T2 = 13.4, p < 0.01), mainly due to the higher values of specific R in sarcopenic obese individuals.ConclusionBIVA detected muscle-mass variations in sarcopenic individuals, and specific BIVA was able to discriminate sarcopenic individuals from sarcopenic obese individuals. These procedures are promising tools for screening for presarcopenia, sarcopenia, and sarcopenic obesity in routine practice.

Vascular Remodeling in Hypertension

Over the past few years noninvasive and invasive techniques have allowed a better appreciation of vascular changes in hypertensive humans and experimental animals.1 Large arteries undergo outward hypertrophic remodeling and increased stiffness with aging,2–4 and in hypertension there may be an acceleration of this process leading to enhanced pulse pressure. A reduced aortic diameter in middle-aged hypertensive subjects may also play a role in increases in pulse pressure through increased specific impedance,5 contradicting the classic hypertensive aortic phenotype characterized by vascular wall degeneration and calcification and increased aortic diameter. In advanced hypertension, however, the elastic laminae undergo duplication and fragmentation, with increased deposition of collagen and fetal (EIIIA) fibronectin, contributing to increased stiffness. Classically the remodeling of small arteries in hypertension has been associated with increased media thickness, but recent studies have demonstrated that 2 types of remodeling are found, inward eutrophic or inward hypertrophic remodeling, depending on whether the media cross-sectional area is enlarged (true hypertrophy).6–9 Although eutrophic remodeling is usually found in essential (primary) hypertension in humans and spontaneously hypertensive rats (SHRs); in secondary hypertension such as in renovascular hypertension, primary aldosteronism, or in pheochromocytoma10; in hypertension associated with diabetes mellitus11,12; and in acromegaly,13 hypertrophic remodeling has been described. In mineralocorticoid hypertension in rodents14,15 and in salt-sensitive Dahl rats,16 in both of which the endothelin (ET) system is activated, remodeling of small arteries is also hypertrophic (see below). Thus, when the renin-angiotensin system is even mildly activated (primary hypertension and SHRs), remodeling is usually eutrophic. In salt-dependent hypertension, diabetes mellitus, and malignant hypertension, all conditions in which the ET system is activated, remodeling is hypertrophic.17 Hyperplasia of vascular smooth muscle cells (VSMCs) is found in small arteries of …

The changes of the frequency specific impedance of the human body due to the resonance in the kHz range in cancer diagnostics

The frequency-specific absorption of kHz signals has been postulated for different tissues, trace elements, vitamins, toxins, pathogens, allergens etc. for low-power (μV) signals. An increase in the impedance of the human body is observed only up to the given power of the applied signal. The highest amplification of the given signal being damped by the body makes it possible to determine the intensity of the given process in the body (e.g. amount of the toxin, trace element, intensity of the allergy) being connected with a given frequency spectrum of the signal.The mechanism of frequency-specific absorption can be explained by means of the Quantum Field Theory being applied to the structure of the water. Substantially high coincidence between the frequencies of the rotation of free quasi-excited electrons in coherent domains of water and the frequencies being used in the MORA diagnostics (Med-Tronic GmbH, EN ISO 13485, EN ISO 9001) can be observed. These frequencies are located in the proximity of f = 7kHz · i (i = 1,3,5,7,…). This fact suggests that the coherent domains with the admixtures of the given substances create structure-specific coherent domains that possess frequency-specific absorption spectra.The diagnostic tool called "MORA System diagnosis" was used to investigate 102 patients with different types and stages of cancer. Many signals were observed to be absorbed by many cancer patients, e.g.: 'Cellular defense system', 'Degeneration tendencies', Manganese, Magnesium, Zinc, Selenium, Vitamin E, Glutamine, Glutathione, Cysteine, Candida albicans, Mycosis. The results confirm the role of oxidative stress, immunological system deficiency and mitochondria malfunction in the development of cancer.

Effect of electrolytes on electrochemical properties of graphene sheet covered with polypyrrole thin layer

AbstractGraphene sheet (GS) was successfully covered with a polypyrrole (PPy) thin layer through in situ chemical oxidative polymerization of pyrrole monomers in aqueous solution by using GS as a support material and ferric trichloride as an oxidant. The resulting nanocomposite was studied by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR) and electrical measurements, including cyclic voltammetry (CV), galvanostatic charge/discharge experiment (GCD), and impedance spectroscopy (EIS). It has been found that the nanocomposite exhibited a typically curved and layer–like structure, and conformational change of PPy chains occurred due to the π–π stacking interaction between the graphitic structures in GS and aromatic rings of the PPy chains. More attention was paid to the effect of electrolytes on electrochemical properties of the nanocomposites, as expected, electrochemical performance was dependent on the nature of the electrolyte, and the neutral electrolytes containing alkali metal ions were found to be very suitable for GS/PPy nanocomposite. Compared with the pure PPy, the nanocomposite possessed larger specific capacitance and lower internal impedance, indicating that the nanocomposite can be a promising candidate as electrode material for supercapacitors.

Analysis of Magnetically Coupled Wireless Power Transmission for Maximum Efficiency

We have proposed and analyzed an equivalent circuit for a magnetically coupled wireless power transmission (WPT) system between two loop resonators by considering its coupling coefficient and radiation-related parameters. A complete formulation is provided for all the necessary circuit parameters. The mechanism of radiation loss is sufficiently explained. The circuit and electromagnetic (EM) simulation results have been shown to be in good agreement. Based on the proposed circuit formulation, a specific load impedance for maximum WPT efficiency was found to exist. The proposed modeling of the WPT in terms of circuit characterizations provides sufficient insight into the problems associated with WPT.

Compact Orthomode Transducer Using Single-Ridged Triangular Waveguides

We present a compact L-band orthomode transducer (OMT) with a new waveguide junction consisting of a quad-ridged square waveguide and four single-ridged triangular waveguides. Quad-ridged square and single-ridged triangular waveguides of various sizes were numerically analyzed to estimate the cutoff frequencies and characteristic impedances of the waveguides. An optimum junction structure for the OMT with a low cutoff frequency and specific characteristic impedance was found based on the numerical simulation. The junction has a relatively small size without waveguide branches, and provides good impedance matching with a 50 Ω coaxial feed line. In addition, Klopfenstein and linear tapers were employed to design waveguide ridges for minimizing mismatches at the OMT junction. Measurement showed a bandwidth of about 400 MHz from 1.0 to 1.4 GHz and an isolation level below -40 dB in the frequency range. The cross section of the OMT was reduced to 62% of the standard waveguide cross section, and the total length is only 56 cm (2.24 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) at 1.2 GHz.

Electrochemical Analysis of Conductive Polymer‐Coated LiFePO4 Nanocrystalline Cathodes with Controlled Morphology

AbstractNanocrystalline LiFePO4 particles and donut‐ and dumbbell‐shaped LiFePO4 microstructures hierarchically constructed with the nanoparticles were synthesized. Coating the surfaces of the LiFePO4 particles with conductive polymers, poly‐3,4‐ethylenedioxythiophene (PEDOT), improved battery characteristics, such as specific capacity, capacity retention, and impedances, by increasing the ionic and electric conductivities of the cathode materials as well as by enhancing the accessibility of lithium ions. The nanocrystalline LiFePO4 that was coated with PEDOT exhibited even larger values than the theoretical value of LiFePO4 at a rate of 1 C or lower rates were observed, with its largest specific capacities of 190 mAh g−1 and 175 mAh g−1 at the rates of 0.2 C and 1 C, respectively, due to the compatibility of the redox characteristics of LiFePO4 and PEDOT. The cathode composed of nanocrystalline LiFePO4 that was coated with PEDOT exhibited the lowest value of the charge transfer resistances (Rct) from the electrochemical impedance analysis.

Power Test of the Ladder IH-RFQ Accelerator at Peking University

A 104-MHz ladder interdigital-H radio frequency quadrupole accelerator (T-IH-RFQ) is developed for applying RFQs to heavy ion implantation and accelerator-based mass spectroscopy in recent years at the Institute of Heavy Ion Physics, Peking University. It could accelerate ions with a mass-to-charge ratio of less than 14, from 2.9 keV/u to 35.7 keV/u within a length of 1.1 m. The T-IH-RFQ cavity operating at H21(0) mode was constructed successfully. Based on a well designed rf power feeding system, the cavity was cold measured and tested with high rf power. In the case of cold measurement, the rf properties were obtained using a vector network analyzer with the help of a perturbation capacitor. During a high power test, the inter-electrode voltage was derived from the energy spectrum of x-rays measured by a high purity Ge detector. The results show that the specific shunt impedance of the T-IH-RFQ cavity reaches 178 kΩm, which could meet the requirements of beam dynamics design.

Adapting Generally Filled Cylindrical Sheet Impedances for Electromagnetic Compatibility [Measurements Corner

The ability to control the bistatic scattering characteristics from cylindrical objects using a tapered cylindrical impedance sheet is presented. It is shown that with the capability to readily control both the real and imaginary components of a percolated lossy film's effective impedance, specific impedance distributions can be obtained to effectively introduce and direct the overall nulls in the bistatic scattering pattern. The bistatic scattering width calculations are based on a modal analysis and an impedance-sheet boundary condition formulation. Potential uses of tapered cylindrical impedance sheets in bistatic EMC/EMI applications are discussed.

Estimation of cardiac output in patients with congestive heart failure by analysis of right ventricular pressure waveforms

BackgroundCardiac output (CO) is an important determinant of the hemodynamic state in patients with congestive heart failure (CHF). We tested the hypothesis that CO can be estimated from the right ventricular (RV) pressure waveform in CHF patients using a pulse contour cardiac output algorithm that considers constant but patient specific RV outflow tract characteristic impedance.MethodIn 12 patients with CHF, breath-by-breath Fick CO and RV pressure waveforms were recorded utilizing an implantable hemodynamic monitor during a bicycle exercise protocol. These data were analyzed retrospectively to assess changes in characteristic impedance of the RV outflow tract during exercise. Four patients that were implanted with an implantable cardiac defibrillator (ICD) implementing the algorithm were studied prospectively. During a two staged sub-maximal bicycle exercise test conducted at 4 and 16 weeks of implant, COs measured by direct Fick technique and estimated by the ICD were recorded and compared.ResultsAt rest the total pulmonary arterial resistance and the characteristic impedance were 675 ± 345 and 48 ± 18 dyn.s.cm-5, respectively. During sub-maximal exercise, the total pulmonary arterial resistance decreased (Δ 91 ± 159 dyn.s.cm-5, p < 0.05) but the characteristic impedance was unaffected (Δ 3 ± 9 dyn.s.cm-5, NS). The algorithm derived cardiac output estimates correlated with Fick CO (7.6 ± 2.5 L/min, R2 = 0.92) with a limit of agreement of 1.7 L/min and tracked changes in Fick CO (R2 = 0.73).ConclusionsThe analysis of right ventricular pressure waveforms continuously recorded by an implantable hemodynamic monitor provides an estimate of CO and may prove useful in guiding treatment in patients with CHF.

Effectiveness of “Thin-Layer” and “Effective Medium” Approximations in Numerical Simulation of Dielectric Spectra of Biological Cell Suspensions

There are a few concerns in dielectric modeling of biological cells by the finite-element method (FEM) to simulate their dielectric spectra. Cells possess thin plasma membranes and membrane-bound intracellular organelles, requiring extra fine meshes and considerable computational tasks in the simulation. To solve the problems, the “thin-layer” approximation (TLA) and the “effective medium” approximation (EMA) were adopted. TLA deals with the membrane as an interface of the specific membrane impedance, and therefore it is not necessary to divide the membrane region. EMA regards the composite cytoplasm as an effective homogeneous phase whose dielectric properties are calculated separately. It was proved that TLA and EMA were both useful for greatly reducing computational tasks while accurately coinciding with analytical solutions.

Simplified calculation of the area specific impedance for battery design

Battery design is a critical aspect of material and system development that leads to the commercialization of effective electrochemical energy storage systems. Successful modeling of battery designs relies upon accurate calculation of the area specific impedance (ASI). A simplified calculation of the ASI is presented that accounts for physical limitations without performing computationally expensive calculations. The limiting currents for transport within the electrolyte and within the intercalation materials are implemented into a linear form of the Butler–Volmer equation to calculate the interfacial impedance. Lithium-ion batteries are then designed to examine the effect of power to energy ratio on battery dimensions. A large ASI is shown to be detrimental to battery design regardless if the increase in impedance results from mass transport limitations or a reduction in electrochemical active area due to small electrode loadings. The smaller electrochemical active area does not increase the voltage losses of a battery when a constant C-rate is maintained. However, the higher ASI values from low electrode loadings require a larger separator and current collector area resulting in a greater battery volume and weight to achieve similar energy and power requirements when compared to a system with a lower ASI.

Single-step fabrication of ABPBI-based GDE and study of its MEA characteristics for high-temperature PEM fuel cells

Single-step fabrication of a Poly(2,5-benzimidazole) (ABPBI)-based gas diffusion electrode (GDE) by directly adding a carbon-supported-catalyst to a homogeneous ABPBI solution prior to deposition and its membrane electrode assembly (MEA) were investigated for high-temperature proton exchange membrane (PEM) fuel cell applications. The ABPBI and LiCl dosages of the catalyst layer were varied. The characterizations of the resulting electrodes and/or MEA for the gas permeability, electrical resistance, specific electrochemical surface area, AC impedance, cyclic voltammetry and high-temperature PEM fuel cell performance were carried out. The high-temperature PEM fuel cell was successfully demonstrated at temperatures of up to 180 °C under ambient pressure operation. The fuel cell performance was evaluated by using dry hydrogen/oxygen gases, which added the advantage of eliminating the complicated humidification system of Nafion cells. The obtained results revealed that a catalyst layer with an ABPBI content of 15 wt.% and an ABPBI/LiCl ratio of 1:2 was sufficient to obtain the optimal cell performance with better electrochemical properties of low cell impedance, high electrochemical activity, low contact resistance and short activation time.

A novel iTongue for Indian black tea discrimination

A novel impedance-Tongue (iTongue) based on multi-electrode Electrochemical Impedance Spectroscopy is proposed for discrimination of Indian black tea. Impedance response of platinum, gold, silver, glassy carbon, polyaniline and polypyrrole working electrodes in tea infusions for a sinusoidal excitation in the frequency range of 1 Hz to 100 kHz has been measured. Also, the percentage of major chemical constituents responsible for the tea quality has been determined by HPLC and UV–vis spectrophotometer. Frequency specific impedance response of these working electrodes along with the determined chemical concentrations was subjected to Principal Component Analysis to confirm the discriminability of the proposed iTongue. The correlations between the frequency specific impedance response of working electrodes and the chemical concentrations which depend on sample variability, such as harvest interval, manufacturing process and brand type have been established. These correlations were further used for dimensionality reduction and discriminability enhancement. The results show that the frequency specific responses of working electrodes play a key role in discrimination of Indian black tea which can be enhanced by combination of working electrodes and their frequency specific responses.

A low-power circuit for piezoelectric vibration control by synchronized switching on voltage sources

In the paper, a vibration damping system powered by harvested energy with implementation of the so-called SSDV (synchronized switch damping on voltage source) technique is designed and investigated. In the semi-passive approach, the piezoelectric element is intermittently switched from open-circuit to specific impedance synchronously with the structural vibration. Due to this switching procedure, a phase difference appears between the strain induced by vibration and the resulting voltage, thus creating energy dissipation. By supplying the energy collected from the piezoelectric materials to the switching circuit, a new low-power device using the SSDV technique is proposed. Compared with the original self-powered SSDI (synchronized switch damping on inductor), such a device can significantly improve its performance of vibration control. Its effectiveness in the single-mode resonant damping of a composite beam is validated by the experimental results.

Structural Vibration Reduction by Switch Shunting of Piezoelectric Elements: Modeling and Optimization

This work deals with the reduction of structural vibrations by means of synchronized switch damping techniques on piezoelectric elements. Piezoelectric patches are attached to the vibrating structure and connected to an electrical circuit that includes a switch. The latter allows to continuously switch the piezoelectric elements from an open-circuit state to a specific electric impedance, synchronously with the mechanical oscillations. The present study focuses on two goals: (i) the quantification of the added damping, (ii) the optimization of the electric circuit parameters, carried out on a one degree of freedom model. The free and forced responses of one mode of the mechanical structure are studied in detail. The precise time response of the system is obtained with semi-analytical models for the two cases where the electrical impedance is a simple resistance (synchronized switch damping on short circuit) or a resistance in series with an inductance (synchronized switch damping on inductor). The damping added by the device is estimated. In all cases, the main result of the study is that the piezoelectric coupling factor is the only parameter to optimize and has to be maximized in order to maximize the added damping. An optimal value of the electric circuit quality factor is obtained when using an inductance, for free and forced response.

Studies on Thermodynamic Properties of Some Imidazolinone Derivatives in DMF at 308.15 K

Density, ultrasonic velocity and viscosity of imidazolinone derivatives are studied in dimethyl formamide (DMF) at 308.15 K. From the experimental data, various acoustical parameters, such as specific impedance Z, isentropic compressibility κ s, Rao's molar sound function R m, van der Waals constant b, relaxation strength r, intermolecular free length L f, internal pressure π, solvation number S n, relative association R A, etc. are evaluated, which helps in understanding the molecular interactions occurring in these solutions.

A hybrid FEM model to simulate the electrical characteristics of biological tissues at the cellular level

Cancer screening is possible with multi-frequency electrical impedance tomography since specific impedance variations are observable as a function of frequency. Through genetic mutations, malignant cells have different cellular characteristics than benign cells and a different impedance signature as a function of frequency. The objective of this project is to develop a FEM model to simulate the electrical characteristics of benign and malignant cells at the cellular level. Traditional tetrahedral element meshing techniques were first considered but the narrowness of the extracellular space and thinness of cell membranes made it impractical since the number of FEM elements quickly reached values that were computationally unmanageable on a typical workstation. We are therefore proposing a hybrid FEM model which combines a standard tetrahedral element meshing technique with 2D surfaces to model the extracellular fluid and discrete electrical components to represent cell membranes. The proposed hybrid modelling approach was used to develop a 3D FEM model of the skin with cellular-level details that can be used to better understand how impedance measurements performed on the skin are affected by lesions as a function of frequency as well as cellular geometrical and electrical parameters.

Inverse boundary and finite element formulations for the determination of high‐frequency specific impedance.

Material databases for consulting acousticians require accurate determination of specific impedance. Such data are typically gathered from the composition of data sets obtained from impedance tubes. In such tubes, the restriction of frequencies under test to those that satisfy a plane wave assumption for the tube geometry in question allows for the application of a one‐dimensional transfer function analysis. Such tubes rarely achieve accuracy at the upper and lower ends of their operating spectra. Thus, the compositing of detailed data sets may produce significant error. For researchers of wave based methods of acoustic wave propagation, this represents a severe limitation. However, these data sets may be re‐purposed for an extension of frequencies under test by the application of an inverse problem formulation of the boundary element method. The method accurately predicts data obtained within a larger impedance tube and further well extrapolates to data observed in a smaller impedance tube. Moreover, the...