Imaginary Part Of Impedance Research Articles

Impedance of Single-Walled Carbon Nanotube Fibers

Impedance measurements of single-wall carbon nanotube (SWCNT) fibers were carried out in the frequency range of 20−106 Hz at temperatures 4.2 < T < 300 K and in the range of applied bias voltage 0−5 V. It was found that in the low frequency range (f ˜ 1–20 kHz) at low temperatures and at bias voltage U > 2 V sign of the imaginary part of impedance was changed from negative to positive, indicating the existence of the crossover from capacitive reactance to inductive one. This crossover was induced by the decrease of height of the energy barriers between nanotubes at the increase of bias voltage. As a result decrease of the impedance of the fibers is accompanied by the rising of the role of kinetic inductance of separate nanotubes.

On the role of grain boundaries in nanocrystalline γ-Fe2O3 under high pressure

In situ impedance spectroscopy of nanophase and bulk γ-Fe2O3 were performed using a fabricated microcircuit on a diamond anvil cell. The results provide evidence for the existence of grain and grain boundary effects that are separated in the frequency region. The analysis establishes that the grain boundary conductance of nanocrystalline γ-Fe2O3 is higher than that of the bulk material. Both the grain and grain boundary resistances of γ-Fe2O3 smoothly decrease with pressure. A remarkable phenomenon of discontinuity appears at 7.4 GPa for the nanocrystals. This critical value is interpreted by the space charge model and changes in charge densities between the grain boundaries. The impedance analysis further reveals that the relaxation frequency gradually increased with the effect of pressure and the γ-Fe2O3 samples’ impedance imaginary part exhibits a typical capacitive characteristic. Within the given pressure range, the relaxation frequency of γ-Fe2O3 follows the Arrhenius behavior. This result was attributed to a dominant interfacial effect.

Adaptive impedance matching system for downlink of passive semi-ultra wideband ultra-high frequency radio frequency identification tag

SUMMARY The input impedance of ultra-high frequency radio frequency identification tag varies with the received power on the chip. It will induce impedance mismatch between the receiver antenna and microchip, thus drastically affect the performance of communication. In this paper, a low cost and fully integrated automatic impedance matching system was presented to solve this problem. It consists of two control loops for independent control of the real and imaginary parts of impedance. The first control loop realizes resistance correction using a parallel LC tuning network, whereas the second control loop achieves reactance compensation using a series LC tuning network. In both loops, the mismatch information is detected for direct control of the variable elements, varactors, which are tuned in a sequential manner. For unambiguous control of the resistance correction, the sign of the intermediate reactance is used as a secondary control criterion to enforce operation into a stable region. The functionality of the proposed automatic matching system was verified for different input impedances of a specifically semi-ultra wideband ultra-high frequency radio frequency identification tag as the available input power varies. The results indicate that all matched impedances are clustered around the target impedance 50 + j0 Ω after acquisition of both loops. Copyright © 2012 John Wiley & Sons, Ltd.

Tissue electrical properties monitoring for the prevention of pressure sore

Pressure sores are a significant problem in the healthcare sector. Although they may cause considerable morbidity, they are preventable. The objectives of this study are to (1) investigate the electrical properties of a tissue close to and away from the pressure sore site, and (2) establish a new approach for objective, reliable, low-cost and noninvasive screening or detection of pressure sore in its early stage. Randomised controlled trial. Fifteen patients participated in this study. They all had stage I or stage II sacral pressure sores. Tiny surface electrodes in four-electrode configuration were used for all tissue electrical properties measurements recorded over the frequency range of 30-10 MHz. Intraclass correlation coefficient (ICC) showed that all measurements (ICC > 0.90 for all measurements) had good reliability and validity. The real part of impedance (R) and the imaginary part of impedance (X) of a tissue measured close to the pressure sore site was found to be significantly smaller (p < 0.05 in all cases) than that measured away from the pressure sore site at a specific frequency range (R: 30.00-38.55 Hz; X: 43.95-606.40 Hz). It was also found that the extracellular resistance (R(e)) and the ratio of extracellular resistance to intracellular resistance (R(e)/R(i)) of a tissue measured close to the pressure sore site were significantly smaller (p < 0.05 in all cases) than that measured away from the pressure sore site. Since the electrical properties (R, X, R(e), R(e)/R(i) ) of a tissue close to, and away from, the pressure sore site can be significantly distinguished, a potentially promising method for the screening of pressure sores at an early stage has been proposed.

Electrical Characterization of Polyethylene oxide -Alumina composite

This study deals with the electrical characterization of polyethylene oxide (PEO) – alumina (Al2O3) composites at several concentrations, 0%, 5%, 10%, and 15% by weight Al2O3. The alternating current electrical properties were studied as a function of frequency in the range from 20 Hz to 1 MHz and studied with filler concentrations. Transmission light microscopy (TLM) and scanning electron microscopy (SEM) revealed that the dispersed Al2O3 particles were randomly distributed within the PEO matrix with some surface contacts between them and also revealed that the ceramic particles are tightly held by the host matrix material. The melting temperature, Tm, was determined for the composites via differential scanning calorimetry (DSC). The AC electrical properties (impedance, real part of impedance, imaginary part of impedance, dissipation factor, dielectric constant, real part of electric modulus, imaginary part of electric modulus, electrical conductivity, and relaxation time) were determined. It was found that the applied frequency and filler concentrations affected the AC electrical properties of the composites. The universal power-law of alternating current conductivity wasobserved in the PEO/Al2O3 composites. The calculated power exponent ( n &lt; 1) is physically acceptable within this applied model.

Dielectric properties and high-temperature dielectric relaxation of tungsten-bronze structure ceramics Ba2GdFeNbTa3O15

Ba2GdFeNbTa3O15 was synthesized by a standard solid-state technique, which adopts a tetragonal filled tungsten bronze structure and exhibits paraelectric nature at room temperature. The dielectric temperature coefficient of Ba2GdFeNbTa3O15 at 1 MHz is 147 ppm °C.−1 AC impedance plots were used as tools to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The conduction is a thermally activated process with activation energy ~1.30 eV. The frequency-dependent maxima in the imaginary part of impedance are found to obey an Arrhenius law with activation energy ~1.34 eV. Such a value of activation energy suggests the existence of a relaxation mechanism (a conductive process), which may be interpreted by an ion hopping between neighboring sites within the crystalline lattice.

AC Impedance Spectroscopy Studies on Zn-Bi-Co-Mn-Ti System Low-Voltage Varistor Ceramics

The electrical responses of Zn-Bi-Co-Mn-Ti system low-voltage varistor ceramics were prepared by solid-state reaction method and were analyzed by AC impedance spectroscopy over a wide range of temperature (100~270°C) in the frequency range of 40~13MHz. The equivalent circuit adopts R (RQ)(RC) model. Imaginary part of impedance and modulus with frequency plot exhibits the varistor ceramics including resistance and capacitance. Impedance analysis enables us to separate the contributions from grains and grain boundaries of our samples. It indicates that grain boundary impedance is the main contributor for ceramic resistance, and grain boundary relaxation effects are most obvious in Zn-Bi-Co-Mn-Ti system. The AC grain boundary conductivity activation energy is attributed to the motion of oxygen vacancies within the bulk, and calculated by Arrhenius equation.

Electrical properties and impedance analysis of Bi0.5Ba0.5FeO3 ceramic

Ba0.5Bi0.5FeO3 ceramic was fabricated by conventional solid-state reaction method. The microstructures and electrical properties were characterized by X-ray diffraction, scanning electron microscopy, direct current (DC) resistance-temperature measurement and alternative current (AC) impedance analysis. According to the analysis, Ba0.5Bi0.5FeO3 ceramic is a cubic perovskite-type compound, and its grain size is about 1.0 μm. In the measured temperature range of 16—280 ℃, Ba0.5Bi0.5FeO3 ceramic shows obvious negative temperature coefficient thermistor characteristic, and the thermistor constant and activation energy of the ceramic are 6490 K and 0.558 eV, respectively. The temperature dependence of dielectric constant reveals that below 280 ℃ no phase transition occurs. The AC impedance characteristic in the ceramic can appropriately be modeled in terms of an equivalent electrical circuit comprising of a series combination of three parallel RQ components in connection with the grain, grain shell and grain boundary effects. The fitting results are in good agreement with the experimental data. The components of grain, grain shell and grain boundary, showing NTC characteristic, have the order of resistive contribution of Rg&gt;Rs&gt;Rgb. In the temperature range 25—115 ℃, the significant mismatch between the peaks of parameters Z″(ω) (imaginary part of impedance) and M″(ω) (imaginary part of electric modulus) suggests a development of persistent localized conduction in Ba0.5Bi0.5FeO3 ceramic.

Electrical Properties of Rare Earth Double Perovskite Sr2CeSbO6

The double perovskite oxide strontium cerium antimonate, Sr2CeSbO6 (SCS) is synthesised by solid state reaction technique. Thermal behaviour of SCS are investigated using thermogravimetric analyser and differential scanning calorimeter in the temperature range from 303 to 1500 K. Dielectric relaxation spectroscopy is used to investigate the frequency dependent dielectric relaxation in SCS in the frequency range from 100 Hz to 1 MHz and in the temperature range from 303 to 703 K. The frequency dependent electrical data are analysed by impedance formalism. The relaxation mechanism of the sample is modelled by Davidson-Cole equation (modified Debye equation). The frequencies corresponding to the maxima of imaginary part of impedance at the various temperatures are found to obey the Arrhenius law with activation energy ∼ 0.15 eV. The scaling behaviour of imaginary part of impedance suggests that the relaxation describes the same mechanism at various temperatures.

Grain boundary effect on the β-boron electrical transport properties at high pressure

Using a diamond anvil cell, the variable-frequency alternate current impedance spectrum of β-boron has been measured upon increasing the pressure from 3.2 to 27.5 GPa. The analysis has established that both the bulk resistance and the grain boundary resistance of β-boron smoothly decrease with the pressure, and that a remarkable phenomenon of discontinuity occurs at 23.9 GPa; this critical value has been interpreted as the pressure threshold above which the van der Waals forces and the interactions between the β-boron grain boundaries significantly emerge. Thence, the grain boundary contribution to the total resistance dramatically declines and results in an enhanced conduction. Besides, the β-boron sample impedance imaginary part exhibits a typical iron-core inductor frequency characteristic.

Frequency and temperature dependent impedance spectroscopy of cobalt ferrite composite thick films

Cobalt ferrite (CoFe2O4) composite thick films consisting of two different sized CoFe2O4 particles were deposited on Pt/Ti/SiO2/Si substrate by a hybridized sol-gel processing and spin coating technique. X-ray diffraction analysis showed a pure spinel phase of CoFe2O4, which was also confirmed by micro-Raman spectra. Scanning electronic microscope indicated a dense microstructure with a thickness above 8 μm. The detailed electrical investigations were conducted in the frequency range of 100 Hz–1 MHz and temperature range between 25 and 200 °C. Real and imaginary parts of impedance (Z′ and Z″) in the above frequency and temperature domain suggested the coexistence of two relaxation regimes: one was induced by electrode polarization; while the other was attributed to the coeffect of grains and grain boundaries, which was totally different from its counterpart of bulks and also not reported in other ferrites. Electrical modulus (M′ and M″) further showed the crossover from grains effect to grain boundaries effect with increasing measured temperature under the suppression of electrode polarization. A non-Debye relaxation behavior and two segments of frequency independent conductivity were observed in dielectric spectra, which was also consistent with the results of ac conductivity spectra. In the conductivity spectra, double power law and single power law were separately applied to the coeffect from grains and grain boundaries and electrode polarization effect. Moreover, the dc conductivity from both effects well obeyed the Arrhenius law and their activation energies were matching to the ones calculated from imaginary impedance peaks, the detailed physical mechanisms on them were finally discussed.

Impedance spectroscopy analysis of double perovskite Ho2NiTiO6

The electrical properties of double perovskite Ho2NiTiO6 (HNT) are investigated by impedance spectroscopy in the temperature range 30–420 °C and frequency range 100 Hz to 1 MHz. The X-ray diffraction analysis reveals that the compound crystallizes in monoclinic phase. The imaginary part of impedance (Z″) as a function of frequency shows Debye type relaxation. The frequency dependence of Z″ peak is found to obey an Arrhenius law with an activation energy of 0.129 eV. Impedance data presented in the Nyquist plot (Z″ vs. Z′) are used to identify an equivalent circuit and to know the bulk and interface contributions. The complex impedance analysis of HNT exhibits the appearance of both the grain and grain-boundary contribution. The results of bulk ac conductivity as a function of temperature and frequency are presented. The activation energy (0.129 eV), calculated from the slope of log τ versus 103/T plot, is found to be the nearly same as calculated (0.130 eV) from dc conductivity. The frequency dependent conductivity spectra obey the power law.

Aggregational processes of low molecular weight polyethylene-b-polyethylene oxide diblock copolymer probed by electrical impedance spectroscopy

In this paper, we analyze the use of electrical impedance spectroscopy (EIS) to investigate the aggregational processes of low molecular weight polyethylene-b-polyethylene oxide copolymer (PE-b-PEO (50% PEO)) induced by concentration. The real and imaginary part of impedance have been compared to theoretical results based on equivalent circuits, providing information pertaining to the properties of the bulk and contributions due to the interactions at the electrolyte/electrode interface. The bulk resistance is used as a convenient tool for identifying structures such as spheres (S), hexagonally packed cylinders (HPC) and lamellar phases. To characterize the transition mechanisms involved in micellization we applied the Phillips criteria, associating the maximum change in the gradient of bulk resistance with the formation of micelles. The transition from micelles to HPC structures is characterized from the minimum in the bulk resistance, while the electrical signature relative to the formation of lamellar structures is characterized by the decrease in the diffusion (reduction in the polarization effects) and the inversion in the slope of bulk resistance as a function of copolymer concentration. Thus, the EIS may be defined as a convenient tool for characterizing the conformation and phase transitions in amphiphilic block copolymers.

Impedance and barrier capacitance of silicon diodes implanted with high-energy Xe ions

Abstract Characteristics of Si p + n diodes with non-uniformly distributed compensating defects, which were introduced by implantation with Xe 23+ ions, have been studied. The layer with the maximum concentration of the compensating defects was located in the vicinity of the metallurgical p – n junction. It is found that the presence of the defect layer results in non-monotonic dependences of the imaginary part of impedance (− Z ″) and differential conductance ( G = −d I /d U ) of the implanted diodes on reverse bias voltage U . An equivalent circuit of the irradiated diode is proposed, which allows us to approximate the measured frequency dependences of capacitance and conductance of the irradiated diodes and to determine values of diode barrier capacitance C pn at different reverse bias voltages.

Fast Impedance Spectroscopy Method for Insulating Layers with Very High Impedance

This paper presents the fast impedance spectroscopy method for objects with a very high impedance |Zx| &ge; 1G&#x2126; modeled by RC networks. The method is suitable for predicting the lifetime and reliability of insulating materials. The fast impedance spectroscopy method was tested on insulating layers which were part of the system metalinsulator-metal (MIM). The method is based on measurements of the power loss and phase shift in the AC voltage divider, which consists of the measured system MIM and of the known impedance. Computer controlled instruments measure the gain and phase shift between the two outputs of alternating electrical circuit and a computer program calculates the parameters of the impedance spectroscopy from these values. The output is the graphical and tabular impedance characteristics of the MIM system, namely: the dielectric loss of the insulating film, imaginary part of impedance, loss factor, parallel resistance Rp and the capacity Cp of the MIM system, all frequency dependent. Frequency characteristics provide an analysis of loss mechanisms that may affect the quality and reliability of the insulating layers.

A preliminary study of the use of bioimpedance in the screening of squamous tongue cancer

Oral cancers are the 11th most common malignancy reported worldwide, accounting for 3% of all newly diagnosed cancer cases, and one with high mortality ratios among all malignancies. The objective of this study was to study the electrical properties of cancerous tongue tissue (CTT) and normal tongue tissue (NTT). Five tongue cancer patients participated in this study. A disposable probe incorporating four silver electrodes was used to measure the electrical properties of CTT and the surrounding NTT of patients. Measurements were performed at six frequencies: 20 Hz; 50 kHz; 1.3 MHz; 2.5 MHz; 3.7 MHz; and 5 MHz, with the amplitude of the applied voltage limited to 200mV. Four measurement parameters of impedance (Z), phase angle (theta), real part of impedance (R), and imaginary part of impedance (X) of tongue tissue were assessed to see if there was any significant difference in the values obtained in CTT and surrounding NTT. The intraclass correlation coefficient showed that all measurements were reliable. A significant difference (P < 0.05 for the four measurement parameters) was found at 50kHz between CTT and surrounding NTT. It was also found that Z and R of CTT were generally smaller than that of surrounding NTT. In conclusion, bioimpedance at a particular frequency is a potentially promising technique for tongue cancer screening.

Adaptive Impedance-Matching Techniques for ControllingLNetworks

The link quality of mobile phones suffers from antenna mismatch due to fluctuating body effects. Techniques for adaptive control of impedance-matching L networks are presented, which provide automatic compensation of antenna mismatch. To secure reliable convergence, a cascade of two control loops is proposed for independent control of the real and imaginary parts of impedance. A secondary feedback path is used to enforce operation into a stable region when needed. These techniques exploit the basic properties of tunable series and parallel LC networks. A generic quadrature detector that offers a power-independent orthogonal reading of the complex impedance value is presented, which is used for direct control of variable capacitors. This approach renders calibration and elaborate software computation superfluous and allows for autonomous operation of adaptive antenna-matching modules.

Acoustic Properties of an Isolated Large-Size Resonator with a Cylindrical Hole

The paper examines the acoustical properties of an isolated large-size resonator with a cylindrical hole. The method for calculating sound absorption and both real and imaginary parts of impedance has been worked out. The results of calculation show that such a resonator absorbs low-frequency sound energy which increases with the enlargement of hole diameter. Sound absorption also depends on the sound wave incidence angle. The dependence of both real and imaginary parts of the hole impedance on frequency, hole diameter and sound wave incidence rate has been established. The results of investigations on the reverberation time, sound absorption coefficients and sound absorption in a model scaled 1:25 are presented.

Dielectric relaxation and electrical conductivity in Bi 5NbO 10 oxygen ion conductors prepared by a modified sol–gel process

Crystalline Bi 5NbO 10 nanoparticles have been achieved through a modified sol–gel process using a mixture of ethylenediamine and ethanolamine as a solvent. The Bi 5NbO 10 nanoparticles were characterized by X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DSC/TG), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and Raman spectroscopy. The results showed that well-dispersed 5–60 nm Bi 5NbO 10 nanoparticles were prepared through heat-treating the precursor at 650 °C and the high density pellets were obtained at temperatures lower than those commonly employed. The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the Bi 5NbO 10 solid solutions were investigated in the 0.1 Hz to 1 MHz frequency range. Two distinct relaxation mechanisms were observed in the plots of dielectric loss and the imaginary part of impedance ( Z″) versus frequency in the temperature range of 200–350 °C. The dielectric constant and the loss in the low frequency regime were electrode dependent. The ionic conductivity of Bi 5NbO 10 solid solutions at 700 °C is 2.86 Ω −1 m −1 which is in same order of magnitude for Y 2O 3-stabilized ZrO 2 ceramics at same temperature. These results suggest that Bi 5NbO 10 is a promising material for an oxygen ion conductor.

Electrical conductivity of wadsleyite at high temperatures and high pressures

The electrical conductivity of wadsleyite aggregates has been determined under the broad range of thermodynamic conditions using the impedance spectroscopy for a frequency range of 10 − 2 to 10 6 Hz. Two branches are observed in the complex impedance, one (at high frequency range) showing a half circle originated at Z′ (real part of impedance) = Z″ (imaginary part of impedance) = 0 in the Z′– Z″ plot, and another branch in the low frequency range. The results from high frequency semi-circles correspond to the electric properties of a sample, whereas the results from a low frequency branch correspond to the electrode effects. From the analysis of the results from the semi-circles, we have identified two distinct mechanisms of electrical conduction having different activation enthalpies and different sensitivity to oxygen fugacity and water content. One mechanism dominating at water-poor condition has a high activation enthalpy (~ 147 kJ/mol) and the conductivity increases with oxygen fugacity. We suggest that electrical conduction in this regime is due to charge transfer involving ferric iron (“polaron” conduction). Under water-rich conditions, electrical conductivity increases with water content but decreases with oxygen fugacity, and the activation enthalpy is smaller (~ 88 kJ/mol). We infer that electrical conduction in this regime is due to protons. The activation enthalpy in this regime is insensitive to water content and the conductivity is proportional to water content, C W, as σ ∝ C w r with r~ 0.72. The value of r is smaller than one suggests that minority defects such as H M′ or H ● are responsible for electrical conduction. Our results show that a completely dry transition zone is incompatible with most of the geophysical observations on the mantle transition zone, and some water (~ 0.1–0.3 wt.% in the Pacific) is required to explain the observed electrical conductivity.