Imaginary Components Of Impedance Research Articles

Co-relation between Rietveld analysis, dielectric studies and impedance spectroscopy of the Ba1−xSrxTiO3 ceramics

Barium strontium titanate (BST), with varying Sr doping levels (x = 0, 0.05, 0.075, 0.1, 0.15, 0.3), was successfully synthesized using the solid-state reaction technique. The aim was to investigate the microstructural, dielectric, and impedance properties as Sr doping increases. X-ray diffraction analysis revealed a tetragonal phase structure for these materials, belonging to the P4mm space group, confirmed via Rietveld refinement using the Fullprof suite. SEM analysis indicated the decrement in grain sizes ranging from 0.198 to 0.0582 μm as doping concentration increases. The temperature and frequency dependencies of the dielectric constant were examined, with the Curie temperature observed in the range of 295 to 351 K with decreasing trend with substitution of strontium in pure barium titanate, showing an increase in dielectric constant with rising temperatures and non-relaxor behavior. P–E loops of BST samples illustrated bulk ferroelectric behavior, with maximum values of retentivity and coercivity reaching 1.56 and 13.97, respectively, in the highly doped BST sample. Various analytical techniques, including Nyquist plots, real and imaginary components of impedance, conductivity measurements, modulus formalism, and determination of charge carrier activation energy, were employed to elucidate the relationships between microstructure and electrical properties. Temperature-dependent resistivity demonstrated the negative temperature coefficient of resistance (NTCR) behavior in Sr-doped barium titanate. Impedance studies revealed semicircular arcs in Nyquist plots, indicating contributions from both grains and grain boundaries. The formation of well-defined grains in the BST samples was further confirmed through modulus spectroscopy.

Structural, Microstructural, and Electrical Properties Study of Pb(Sn0.45Ti0.55)O3 Ceramics

We undertook a comprehensive investigation of the the structural, dielectric, and electrical characteristics of Pb(Sn0.45Ti0.55)O3 ceramics prepared using the conventional solid-state route. A meticulous preparation protocol, involving solvating various precursors, was followed by extensive characterization employing X-ray diffraction, scanning electron microscopy, and dielectric studies. The synthesized sample features a single-phase tetragonal structure with P4mm symmetry. Using impedance spectroscopy, electrical transport properties of the polycrystalline Pb(Sn0.45Ti0.55)O3(PST) ceramic were studied in detail. Relaxation and conduction mechanisms of the material were inferred using complex impedance, complex electric modulus, and frequency dependent ac conductivity analysis. Impedance spectroscopy results reveal the range of frequencies in which the grain, grain boundary, and electrode effects are dominant. Above certain temperatures, the imaginary component of impedance (Z//) exhibits some resonant type peaks at different frequencies indicating relaxor nature of the sample. The activation energy obtained for both the relaxation and conduction process indicates the role of doubly-ionized oxygen vacancy in the conduction mechanism of the sample. The dielectric relaxation occurring at low frequency and high temperatures is related to the space charges associated with the ionized oxygen vacancies being trapped at the grain boundaries. The Cole-Cole plots confirm the poly-dispersive nature of dielectric relaxation in the sample.

Imaginary impedance due to hopping phenomena and evaluation of dopant ionization time in cryogenic metal-oxide-semiconductor devices on highly doped substrate

MOS capacitors fabricated on substrates with doping concentrations as high as 1018 cm−3 were characterized at 4.2 K. The highly doped substrate exhibited an intrinsic imaginary component of impedance at 4.2 K. The imaginary component is attributed to the time delay induced by hopping phenomena, leading to a decrease in the gate capacitance. Furthermore, we investigated the time constant associated with dopant ionization under depletion conditions and determined it to be 0.35 μs. An equivalent circuit model of the highly doped substrate at 4.2 K is also shown.

KINETICS OF CATHODIC HYDROGEN EVOLUTION ON MOLYBDENUM DISILICIDE IN ACID SULPHATE MEDIA

The kinetics and mechanism of hydrogen evolution on the MoSi2 electrode in x M H2SO4 + (0.5 - x) M Na2SO4 (x = 0.50; 0.35; 0.20) solutions have been studied. The cathodic polarization curves of MoSi2 in the studied solutions are characterized by Tafel region with a slope of (-0.070)±0.002 V. The reaction order of the cathodic process with respect to hydrogen ions at the potentials of Tafel region is ~1.0; the derivative of the electrode potential with a change in electrolyte acidity is ~0.072 V. The impedance spectra of the MoSi2 electrode in the studied potential range have the shape of a semicircle located in the capacitive half-plane, with the centre in the region of positive values of the imaginary impedance component; in the region of the highest frequencies, a short straight section is recorded on the impedance plots, indicating the presence of pores in the surface layer of the electrode. To describe the hydrogen evolution reaction on MoSi2, we used an equivalent electrical circuit, the Faraday impedance of which consists of series-connected charge transfer resistance (R1) and a parallel R2C2Zd-chain responsible for the adsorption of atomic hydrogen on the surface and its diffusion into the depth of the electrode material. The equivalent circuit also includes the solution resistance (Rs) and the double layer capacitance impedance, which is modeled by the constant phase element CPE1. It is shown that the hydrogen evolution reaction on molybdenum disilicide in a sulphuric acid electrolyte proceeds along the discharge - recombination route with a quasi-equilibrium discharge stage when the Temkin logarithmic isotherm for adsorbed atomic hydrogen is fulfilled. The hydrogen evolution reaction is complicated by hydrogen absorption proceeding in the mode of solid-phase diffusion kinetics.

Tailoring the structural and dielectric properties of ZnFe2O4 through annealing temperature

In this study, we synthesized nano-crystalline ZnFe2O4 through the sol-gel method and explored the impact of annealing temperature on its physical properties. The average crystallite size, determined using the Debye-Scherres's formula with data obtained from Rietveld-refined X-ray diffraction, increased from 16 nm to 58 nm as the annealing temperature rose from 200 to 1000 K. FTIR spectra showcased vibrational modes corresponding to metal-oxygen bonds at both octahedral and tetrahedral sites. UV–Vis DRS measurements uncovered a widening of the optical band gap from 2.03 eV to 2.14 eV with increasing annealing temperatures. The rearrangement of cations exerted a substantial influence on the dielectric properties and AC conductivity. Dielectric assessments illustrated a diminishing trend in both the real and imaginary components of impedance as frequency progressed, decreasing from 107 at 100 Hz to 10 at 100 MHz. Additionally, conductivity investigations emphasized that the AC conductivity of ZnFe2O4 experiences enhancement at higher frequencies.

Structural, electrical and dielectric properties of ZnFe2O4/Cu2S 3D heterostructures

This work reports the fabrication of zinc ferrite-copper sulphide (ZnFe2O4/Cu2S) 3D heterostructures and subsequent investigation of the spectroscopic behaviour of various electrical parameters like conductivity, impedance and dielectric loss. The study reveals a non-monotonic behaviour of the real component of impedance (Z’), while the imaginary component of impedance (Z’) exhibits a temperature-dependent relaxation frequency, with an estimated activation energy (E a ) of 220.13 meV. The dc conductivity (σ dc ) measurements reveal the semiconducting nature of the sample and a transition from a ferrimagnetic to a paramagnetic behaviour is reported at the Curie temperature of 327 K. In case of ac conductivity (σ ac ), Jonscher’s power law σ ac = Aω n is followed and the exponent n is found to lie in the range 0.679–0.735 at different temperatures, which is best fitted into a polynomial of degree six. The temperature variation of n is suggestive of the overlapping large polaron tunnelling (OLPT) model. Further, ac activation energy (E ac ) is also calculated, which is found to be smaller than the dc activation energy (E dc ), indicating electron hopping between Fe3+ and Fe2+ ions. The numerically computed staying time (τ) of electrons in Fe3+/Fe2+ ionic sites varies with frequency as well as with temperature, ranging from 10−6s to 10−19s. A significant decrease in dielectric loss (tanδ) to the tune of 99% (from 75 at ∼100 Hz to 0.89 at ∼1 MHz) is reported at room temperature. In the present scenario, when smart materials like spinel ferrites have garnered significant attention for their promising magnetic and electric properties, our studies of the ZnFe2O4/Cu2S 3D heterostructures may provide immense possibilities for tailored applications in various electromagnetic applications.

Artificial Neuronal Networks for the Prediction of Atmospheric Corrosion in Bronze with Nanostructured Patinas with SiO2

Introduction Atmospheric corrosion is the main cause of metallic heritage degradation when they are exposed to relative humidity, temperature cycle and air contaminants. Corrosivity maps are one of the preventive strategies for atmospheric corrosion mitigation, but they do not provide enough information about corrosion mechanism, besides that long experimentation periods are required [1]. Moreover, electrochemical techniques are alternatives to speed up results, but their relationship with constantly changing environmental variables is difficult to control.Currently, Artificial Intelligence has been introduced in corrosion engineering studies, because of its capability to make predictions based on big data. Also, experimental data of Electrochemical Impedance Spectroscopy had been used in Artificial Neural Network training to obtain Nyquist Diagrams [2]. The objective of this work is to obtain computational models of Artificial Neural Networks to predict atmospheric corrosion in Bronze with nanostructured patina with SiO2, in marine environments. Method Environmental parameters were taken from database previously reported [3,4], and from Civil Protection Secretariat of Veracruz. Whilst electrochemical evaluation consists in Polarization Resistance and Electrochemical Impedance Spectroscopy; they were carried out in a Gamry Interface 1000 Potentiostat with a Saturated Calomel Reference Electrode (SCE) and a graphite bar as counter electrode in an agar gelled cell. Meanwhile, working electrode was bronze with nanostructured patina with SiO2. Two patina were prepared, the first with CuSO4 solution (0.015 mol L-1) and the second applying a CuNO3 solution (20% wt).The 13 variables used in the database for Artificial Neural Networks (ANN) training were: exposure time, chloride concentration, sulfur compounds concentration, relative humidity, precipitation level, windspeed, temperature, nanocoating presence, corrosion potential, corrosion rate, frequency, real and imaginary component of impedance. The values of each variable were treated with measures of central tendency and dispersion, as well as correlation matrix and histograms, which allowed to find a relationship between variables, and choosing the inputs for ANN. The prediction models consisted in 5, 9, 10 and 12 neurons in the input layer (R5E, R9E, R10E and R12E, respectively), a hidden layer, and Zima as only neuron in the output layer. The number of neurons in hidden layer varied from 1 to 8 until the highest coefficient of determination was achieved. The computational model was performed using the toolbox in MATLAB with a feedforward ANN. It is worth mention that the hidden and output layers used a hyperbolic tangent and a linear transfer function, respectively, and a Levenberg-Marquardt algorithm as training function was used in the models. Results and Conclusions Figure 1 presents the coefficient of determination (R2) and root mean squared error (RMSE) with different ANN architectures. In the four models, the highest value was reached with 8 neurons in the hidden layer. Then, the linear regressions for R5E, R9E, R10E and R12E models and 8 neurons in the input layer were compared in Figure 2. In that sense, the Nyquist Diagrams in Figure 3 were simulated with the R9E and R12E models. Also, they were compared with experimental Nyquist Diagrams for Bronze with patina of CuSO4 and CuNO3, with and without SiO2 nanoparticles, at 56 days of exposure in marine atmospheres. The simulations demonstrated how an ANN model with 12 neurons in the input layer, 8 neurons in the hidden layer and 1 neuron in the output layer can be used as a corrosion prediction model of bronze with nanostructured patina with SiO2.

Light Intensity Modulated Photo-Electrochemical Methods and Distribution of Relaxation Times As Tools to Investigation Photovoltaic Materials

Electrical Impedance Spectroscopy (EIS, sometimes also Electrochemical Impedance Spectroscopy) found its place in material studies as a routine experiment. EIS proliferation became possible through advances in electronics. Current-voltage characteristics were standard features of potentiostats. Impedance techniques require additional components embedded into a potentiostat, namely signal generator and signal analyzer. Relatively simple devices are available, although dedicated instrumentation with little noise, broad frequency control and perhaps sample temperature control or automated sample handling are particularly desired and command premium in cost.EIS as an electrical technique uses as the perturbing signal alternating electrical signal, either potential of current. In general, impedance studies are intended to study a transfer function and the input and output do not have to be only voltage-current or current-voltage as it would be in EIS. In mechanical engineering are for example useful studies focused on mechanical perturbation. Electrical response by its nature makes EIS amenable to study electrochemical systems.Along with the impedance vs. frequency data collection comes also the need of meaningful data interpretation. This is typically done through data fitting to components of an equivalent electrical circuit. The acquired data -- real and imaginary impedance components gathered over a vast range of frequencies -- are evaluated by fitting to some equivalent circuit using nonlinear regression.Oftentimes both finding the equivalent circuit and the physical component assignment are tedious, if not impossible. Recently a new approach to data reduction has been a treatment via distribution of relaxation times (DRT) [1, 2]. In principle, this approach has been outlined already in 1936 [3]. Its present use was made possible by available computation power of current PCs [4, 5]. While this is not a substitute to equivalent circuits and subsequent physical data interpretation, it is possibly a method, when used appropriately and in automated way, that can provide more information that simple comparison of the Bode or Nyquist graphs. This note is presenting some examples of this approach.In the field of photovoltaic studies of light-gathering materials experimentation on systems responding to illumination makes use of impedance studies in which the perturbing signal is light of certain wavelength (or white light) with variable intensity. Here we will look at the link between EIS and electrical response spectroscopy induced by fluctuating light. This is sometimes for short dubbed as optical spectroscopy although it does make a use of the instruments for optical spectroscopy (such as UV-VIS, IR etc.) as they are known from analytical chemistry literature. Rather, an electric signal in a photoactive material is generated by intensity modulated light at different frequencies (similar range to electrical impedance spectroscopy) and a response (the magnitude and the phase shift) is analyzed. In this respect the magnitude and phase shift correspond to the magnitude and a vector of resistance on the polar plot of electrical impedance measurement. However, the data obtained serve a different purpose. For example, in a photovoltaic shorted system, the time constant associated with the response corresponds to mobility of the photogenerated charge in the material. For an open-circuit potential of such a photovoltaic system the measured time constant response corresponds to the rate of recombination of the generated hole-electron species.Such materials of general structure (ABX3) could be replacements for silicon-based photovoltaic cells. These materials, due to the possible variability of both cations and anions in their composition, offer almost endless possibilities for synthetic preparation. For the active layer of a solar cell is often used the CH3NH3PbI3-2Cl2 perovskite structure, i.e., a structure containing an organic component. We have built and then tested such photovoltaic cells by static and dynamic methods using a unique photoelectric research instrument using the method CIMPS (Controlled Intensity Modulated Photocurrent Spectroscopy).AcknowledgementThis work was supported through the support of The Czech Science Foundation (GACR), contract GA19-23718S.References BioLogic, Distribution of Relaxation Times (DRT): an introduction, BioLogic, Editor. 2017.Weese, J., A reliable and fast method for the solution of Fredhol integral equations of the first kind based on Tikhonov regularization. Computer Physics Communications, 1992. 69(1): p. 99-111.Yager, W.A., The Distribution of Relaxation Times in Typical Dielectrics. Physics, 1936. 7(12): p. 434-450.Shoar Abouzari, M.R., et al., On the physical interpretation of constant phase elements. Solid State Ionics, 2009. 180(14): p. 922-927.Wan, T.H., et al., Influence of the Discretization Methods on the Distribution of Relaxation Times Deconvolution: Implementing Radial Basis Functions with DRTtools. Electrochimica Acta, 2015. 184: p. 483-499.

PASSIVE UHF RFID TAGS WITH THERMAL-TRANSFER-PRINTED ANTENNAS

Papers for the thermal transfer printing of UHF RFID antennas were prepared by coating and calendering. Real and imaginary components of the impedance of the UHF RFID antennas depended on their design, coating composition and conditions of paper calendering. Passive UHF RFID tags were constructed from antennas and chips whose real and imaginary components of impedance in the 860–960 MHz frequency band were at approximately the same level. The communication quality of passive UHF RFID tags was evaluated by measuring the reading range using the designed UHF RFID reading unit. The reading range of experimental UHF RFID tags with printed antennas on paper and commercial UHF RFID tags with chemically etched antennas on a PET film were identical in the 860 MHz frequency.

Lithium-ion mobility in layered oxides Li2Ca1.5Nb3O10, Li2Ca1.5TaNb2O10 and Li2Ca1.5Ta2NbO10, enhanced by supercell formation

Lithium ion conductivity in layered oxides Li 2 Ca 1.5 Nb 3 O 10 , Li 2 Ca 1.5 TaNb 2 O 10 and Li 2 Ca 1.5 Ta 2 NbO 10 is improved over their Sr-analogue due to the formation of a supercell. The greater mobility of lithium is confirmed by dielectric and complex modulus analyses. The formation of a supercell and its impact on lithium-ion conductivity have been studied through synthesis of three layered oxides, Li 2 Ca 1.5 Nb 3 O 10 , Li 2 Ca 1.5 TaNb 2 O 10 and Li 2 Ca 1.5 Ta 2 NbO 10 , related to Ruddlesden-Popper structure-type. Neutron diffraction experiments show that these materials feature a supercell, which is significantly larger (~√2 a × ~√2 b × ~ 1 c ) than that of a typical Ruddlesden-Popper oxide. Electrochemical impedance spectroscopy shows that the formation of the new supercell is associated with enhanced lithium-ion conductivity of these materials as compared with the Sr-analogue, Li 2 Sr 1.5 Nb 3 O 10 , which lacks the supercell. In addition, a systematic trend is observed in the ionic conductivity: Li 2 Ca 1.5 Ta 2 NbO 10 < Li 2 Ca 1.5 TaNb 2 O 10 < Li 2 Ca 1.5 Nb 3 O 10 . The Arrhenius analysis in the temperature range 25–400 °C shows that activation energy for the temperature-dependent rise in conductivity follows a similar trend. Detailed analyses of real and imaginary components of impedance, dielectric properties, tangent loss, and complex modulus show the systematic increase in lithium-ion mobility. The dielectric values mirror the same trend as ionic conductivity, where the most conductive material shows the highest dielectric properties. In addition, the same trend is observed in the peak and dispersion of dielectric loss and complex modulus as a function of angular frequency, indicating a systematic rise in lithium-ion mobility. This fundamental study is aimed at exploring the impact of structural modifications on ionic conductivity in solids.

Photovoltaic, capacitance-voltage, conductance-voltage, and electrical impedance characteristics of p-type silicon/intrinsic-silicon/n-type semiconducting iron disilicide heterostructures built via facing target direct-current sputtering

p-Type silicon (Si)/intrinsic Si/n-type semiconducting iron disilicide heterostructures were built via facing target direct-current sputtering. To assess the photovoltaic properties, the current density-voltage characteristic curves were recorded in conditions of dark and under irradiation via an Air Mass 1.5 solar simulator (100 mW/cm2). The built heterostructures demonstrated effective rectifying behavior along with a rather substantial leakage current. The open-circuit voltage and the short-circuit photocurrent density values were 178.00 mV and 10.08 mA/cm2, respectively. The assessed energy conversion efficiency was approximately 0.75%. The series resistance (Rs) values at 0 V appraised by the Nicollian-Goetzberger technique were 60.28 Ω at 2 MHz, and 4.13 × 103 Ω at 10 kHz. Their interface state density values evaluated through the Hill-Coleman method were 1.38 × 1012 cm−2/eV at 10 kHz and 1.31 × 1011 cm−2/eV at 2 MHz. The Rs and interface states occurring in the heterostructure interface zone should be the potential determinant of the degeneration of the photovoltaic properties. The characteristics of the real (Z’) and imaginary components of impedance under the changing voltages manifested a shape of one semicircle having a semicircular midpoint beneath the Z’ coordinate. An equivalent circuit model that was related with the heterostructure behavior should be assembled from the parallel association of resistance and constant phase element connected with Rs.

Rate-Limiting Steps Elucidated By Electrochemical Impedance Spectroscopy of a Yttria-Stabilized Zirconia 2-in-1 Temperature and Oxygen Gas Sensor Measured at Extreme Temperatures

Introduction Yttria-stabilized zirconia (YSZ) is known for its good ionic conductivity, essentially being synonymous with the term “lambda sensor”. Automotive lambda sensors have been fabricated with YSZ as the electrolyte for 30+ years and have operated in a temperature region of 600oC to 800oC. There is an increasing demand for higher operating temperature sensors, specifically a 2-in-1 temperature and oxygen sensor which is stable, selective, and sensitive in extreme environments. However, there remains a disagreement among scholars about the effects on oxygen vacancy activation energy at temperatures higher than 800oC. Also, the rate-limiting step of oxygen reduction on the platinum electrode is not inherently clear. A 2-in-1 temperature and oxygen sensor was fabricated and characterized with the analysis of electrochemical impedance spectroscopy (EIS), DC resistance, and open circuit potential measurements at temperatures between 600oC and 1200oC. The temperature dependence on individual activation energies within the sensor was elucidated directly through these techniques. Methods Yttria-stabilized zirconia (MTI Corp) was employed as the solid-state electrolyte in sensor fabrication, with the primary electrode material as porous platinum (ESL 5570). Platinum paste was screen printed onto planar YSZ substrates in an interdigitated electrode configuration, then fired at 1500oC for 2 hours in nitrogen atmosphere (1 atm). The sensor was placed in a ThermoScientific tube furnace capable of reaching 1500oC, with mass flow controllers varying oxygen gas concentration throughout electrical measurements. Platinum foil acted as a Faraday cage around the sensor to shield from furnace inductive fluctuations and minimize noise during low frequency EIS measurements. A thermocouple placed next to the sensor validated furnace operating temperature and cooling endcaps on the furnace tube created a natural temperature gradient between sensor placement and the electrical connections outside of the furnace. Figure 1 displays the environmental testing setup. Results and Conclusions Figure 2a displays an impedance Nyquist spectrum that contains real and imaginary components of impedance measured at 0.21 atm PO2, where electrolyte resistance decreases with an increase in temperature. Figure 2b displays the Arrhenius plot of isolated YSZ electrolytic resistance extracted from figure 2a, where there are distinct activation regions at moderate and high temperatures. In agreement with Badwal [1], the shift to lower EA at higher temperatures was due to a gradual transition between an association region where oxygen vacancies are bound to dopant cations, and a dissociation region where vacancies are free and mobile.At a known temperature, EIS also elucidates oxygen concentration dependence on sensor electrode resistance. Figure 3a shows sensor electrode resistance, fitted from figure 2a, as a function of oxygen concentration. Investigating the oxygen reduction reaction (ORR) variation on platinum at various temperature regions, it is suggested that ORR on platinum is co-limited by oxygen adsorption and by oxygen transport along the surface of the electrode, in agreement with Adler [2]. Figure 3b shows that electrode 2 is dominant at temperatures below 1050oC, indicative of oxygen diffusion limitation on the surface and through platinum. Electrode 1 is dominant at temperatures above 1050oC, where dissociative adsorption of oxygen on the electrode surface is predominant.

An Experimental Characterization of the Impedance and Spectral Content of Multistable Structural Responses During Dynamic Bifurcations

The ability to predict multistable structural dynamics challenges the development of future high-performance air vehicles that will be subjected to extreme multiphysics loads. To aid in the establishment of methodologies that characterize the response states of harmonically excited multistable structures, a catalog of empirical and practical evidence is necessary. Recent research has suggested that evolving aspects of mechanical impedance metrics may be correlated with measurable quantities, although their relation to bifurcations of the dynamic response remains incompletely understood. Motivated to begin establishing such knowledge base, this research seeks to construct a library of experimental evidence from which to draw generalized insights on the impedance- and spectral-changing trends of multistable structures undergoing severe nonlinear response due to harmonic loading. A connection between vanishing real and imaginary components of impedance and dynamic bifurcations is uncovered. In the process, a technique to forecast dynamic bifurcations is articulated, which utilizes mechanical impedance measurements in real-time to monitor the susceptibility of postbuckled structural components to undergo dynamic bifurcations. An examination of higher-order harmonics of the dynamic responses further illuminates the nearness to bifurcations and may help classify the precise response regime. Thus, by correlating the real-time impedance and spectral response with analytical predictions, a future tool may be established for condition monitoring and diagnosis.

Electric Conductivity Changes in Geopolymer Samples with Added Carbon Nanotubes

By incorporation of nanotubes to the current composite materials, their properties can be significantly improved. Carbon nanotubes can act as filler, which minimizes the air gaps content in the matrix. The denser structure positively affects the physical and mechanical properties of the whole composite. The paper deals with alkali-activated materials (AAM) based on finely-ground granulated blast furnace slag modified by carbon nanotubes. Prismatic samples of this type of AAM were prepared with addition of 0.1 – 0.4wt. % of carbon nanotubes (with 0.1% step). The change of electrical parameters (electrical capacity, relative permittivity, real and imaginary impedance component) was observed. The obtained results indicate that the absolute value of the impedance decreases with increasing amount of carbon nanotubes and relative permittivity shows the general increase. The results may contribute to further research and development of alkali-activated systems, focusing on practical applications in construction.

HIGH-FREQUENCY ELECTRICAL PROPERTIES OF AN AMORPHOUS SOFT MAGNETIC WIRE ON THE BASIS OF COBALT, HELD NANOCRYSTALLIZATION ANNEALING

The features of the changes of the real and imaginary components of the impedance in the restructuring of the amorphous soft magnetic Co66Fe4Nb2.5Si12.5B15 wires due to direct current annealing have been revealed. The difference in the behavior of the frequency dependences of the impedance component with increasing current density annealing has been determined. The frequency range with a dominant sensitivity of the imaginary component of impedance to the structural changes in the wire compared to the real one has been detected. The results are explained on the basis of the ideas on restructuring the atomic and domain structure of the wire caused the annealing by a direct current, subject to the differences in the behavior of the components of the dynamic magnetic permeability with changing the frequency of the alternating current.

Effect of dysprosium substitution on electrical properties of SrBi4Ti4O15

SrBi4−xDyxTi4O15 (with x = 0.02, 0.04, 0.06 and 0.08) powders have been synthesized using the stoichiometric amounts of nitrates and oxides of the constituent materials through sol–gel method. The compound so formed is characterized using X-ray diffraction. The density and lattice parameters are calculated. The impedance and electrical conductivity properties are investigated. The imaginary part of impedance as a function of frequency shows Debye like relaxation. Impedance data presented in the Nyquist plot which is used to identify an equivalent circuit and the fundamental circuit parameters are determined at different temperatures. The results of bulk a.c. conductivity as a function of frequency at different temperatures are presented. The dielectric behavior was investigated. Permittivity was calculated based on the relaxation frequency using an alternative approach based on the variation of the imaginary impedance component as a function of reciprocal angular frequency. The frequency dependence of real and imaginary permittivities was also investigated.

Admittance to detect alterations in left ventricular stroke volume.

Implantable cardioverter-defibrillators monitor intracardiac electrograms (EGMs) to discriminate between ventricular and supraventricular tachycardias. The incidence of inappropriate shocks remains high because of misclassification of the tachycardia in an otherwise hemodynamically stable individual. Coupling EGMs with an assessment of left ventricular (LV) stroke volume (SV) could help in gauging hemodynamics during an arrhythmia and reducing inappropriate shocks. The purpose of this study was to use the admittance method to accurately derive LV SV. Ultrasonic flow probe and LV endocardial crystals were used in canines (n = 12) as the standard for LV SV. Biventricular pacing leads were inserted to obtain admittance measurements. A tetrapolar, complex impedance measurement was made between the Bi-V leads. The real and imaginary components of impedance were used to discard the myocardial component from the blood component to derive instantaneous blood conductance (Gb). Alterations in SV were measured during right ventricular pacing, dopamine infusion, and inferior vena cava occlusion. Gb tracks steady-state changes in SV more accurately than traditional magnitude (ie, |Y|, without removal of the muscle signal) during right ventricular pacing and dopamine infusion (P = .004). Instantaneous LV volume also was tracked more accurately by Gb than ∣Y∣ in the subset of subjects that underwent inferior vena cava occlusions (n = 5, P = .025). Finite element modeling demonstrates that admittance shifts more sensitivity of the measurement to the LV blood chamber as the mechanism for improvement (see Online Appendix). Monitoring LV SV is possible using the admittance method with biventricular pacing leads. The technique could be piggybacked to complement EGMs to determine if arrhythmias are hemodynamically unstable.

16-Channel CMOS Impedance Spectroscopy DNA Analyzer With Dual-Slope Multiplying ADCs

We present a 16-channel, mixed-signal CMOS DNA analyzer that utilizes frequency response analysis (FRA) to extract the real and imaginary impedance components of the biosensor. Two computationally intensive operations, the multiplication and integration required by the FRA algorithm, are performed by an in-channel dual-slope multiplying ADC in the mixed-signal domain resulting in minimal area and power consumption. Multiplication of the input current by a digital coefficient is implemented by modulating the counter-controlled duration of the charging phase of the ADC. Integration is implemented by accumulating output digital bits in the ADC counter over multiple input samples. The 1.05 mm×1.6 mm prototype fabricated in a 0.13 μm standard CMOS technology has been validated in prostate cancer DNA detection. Each channel occupies an area of only 0.06 mm² and consumes 42 μW of power from a 1.2 V supply.

The Effects of Membrane Thickness on the Performance and Impedance of the Direct Methanol Fuel Cell

The purpose of this work is to investigate the effect of membrane thickness on direct methanol fuel cell (DMFC) performance and impedance under various operating conditions including operating temperature, methanol concentration, cathode flowrate, and cathode backpressure. The experiments were conducted by using three membranes of NRE-212 (50.8 m), N-115 (127 m), and N-117 (183 m) loading Pt—Ru (4 mg/cm&lt;sup&gt;2&lt;/sup&gt;) and Pt-black (4 mg/cm&lt;sup&gt;2&lt;/sup&gt;) at the anode and the cathode, respectively. The DMFC performance was analysed in terms of a polarization curve expressed by measuring voltage and current density and power—current density. In order to analyse performance losses such as activation loss and ohmic loss, the real and imaginary components of impedance were measured by AC impedance measurement system at various frequencies. Also, the crossover current at the open circuit was measured by using humidified nitrogen at the cathode and power supply. It was shown that DMFC performance was improved by the reduction of resistance for proton transport at the thinner membrane under the same test conditions. The comparison of open circuit voltage shows that using of a thicker membrane results in a larger value than that of using a thin membrane due to the decrease in methanol crossover.

Investigation of the electroreduction of silver sulfite complexes by means of electrochemical FFT impedance spectroscopy

The electroreduction kinetics of silver sulfite complexes was investigated by electrochemical fast Fourier transform (FFT) impedance spectroscopy (0.061–1500 Hz). The time dependences of the real and imaginary components of impedance were determined in a solution containing 0.05 M Ag (I) and 1 M Na 2SO 3. The mean duration of silver ad-atom diffusion on the surface to the nearest crystallization centre was calculated: during the first 210 s of contact with the electrolyte, these values increase from 0.66 up to 1.77 s; thereafter, this variation stabilizes and the mean duration of silver ad-atom diffusion reaches an almost constant value (1.56 s).