Abstract: AC-impedance spectroscopy (AC-IS) was combined with time-domain reflectometry (TDR) to investigate the impedance response of fiber-reinforced cement (FRC) composites with multi-walled carbon nanotubes (MWCNTs). In Nyquist plots (−imaginary impedance vs. +real impedance) three impedance arcs/features were observed, similar to Nyquist plots for macrofiber and microfiber FRCs. The intersection of the electrode arc and the intermediate frequency feature ( R DC (FRC)) corresponds to the DC resistance of the composite. The intersection of the two bulk features ( R cusp ) corresponds to the AC resistance of the composite. Reductions in ( R DC (FRC)) from the matrix resistance are indicative of a nanotube percolating network. Reductions in R cusp from the matrix resistance are indicative of a discontinuous fiber–fiber path. Both shifts increased with fiber loading. AC-IS measurements are therefore able to discriminate percolation vs. discontinuous fiber effects in CNT-FRCs, with the potential for characterizing dispersion issues (e.g., clumping/aggregation) in nanocomposites.

Abstract: Two- and four-probe cells were designed for comparative studies of ionic conductivity of proton conducting membranes (PEMs) using electrochemical impedance spectroscopy. Nafion 115 membrane was employed to examine the influence of cell configuration, probe geometry, and arrangement of probe. Whereas a single arc and linear responses, were observed in Nyquist plots using the 2-probe cell, multiple arcs were observed using the 4-probe cell. The linear response observed in the 2-probe configuration and the low frequency arc observed in the 4-probe configuration are due to transmission line behavior that results from a distributed interfacial capacitance coupled with the membrane's ionic resistance at the Pt/PEM interfacial region. Increasing the distance between the probes and/or reducing the electrode contact area reduces or eliminates these low-frequency artifacts so that accurate data for ionic resistance can be obtained. Equivalent circuits for 2-probe and 4-probe cell geometries are constructed and used to extract conductivity data.

Abstract: Nanosized ceramic powder having a general formula Pb1-xMgxZr0.05Ti0.95O3 (PMZT) with x=0, 0.03, 0.06 and 0.09 has been synthesized by a metal ion complex precursor solution method. Preliminary structural analysis of PMZT compounds using the X-ray diffraction technique suggests that they exhibit a single phase with tetragonal crystal structure. Complex impedance spectroscopy analysis has been carried out to investigate the electrical properties. The physical structure of the samples has been visualized most prominently near 400 °C from the Nyquist plot as consisting of grains separated by grain boundaries. The presence of a single arc in the complex modulus spectrum at different temperatures confirms the single-phase character of the PMZT compounds.

Abstract: It will be shown in this contribution that if the thermal impedance Zth(jw)of an electronic package is represented in a Nyquist plot, the curve obtained can be fitted very well to a combination of a few (n) circles, n varying between 2 and a maximum of 5. For each of these circles, it is sufficient to know the radius and the coordinates of the center point or just three parameters. With 3n parameters the entire behavior of the impedance can be represented and consequently, the dynamic behavior as well.

Abstract: Two TiO2 coatings were plasma sprayed, using an aqueous suspension as a feedstock onto initially prepared alumina substrates. Their thickness was about 7 and 15 μm. The coatings were tested using impedance spectroscopy (IS) in the frequency range from 100 Hz to 2 MHz at temperatures ranging from 320 to 1020 K. The measurements allowed to find the Nyquist plots and equivalent circuits of the tested samples. The IS results were interpreted by the microstructural features of the deposits such as chemical composition, atomic structural and phase analysis. The mechanism of electric current conduction in tested coatings was proposed. © 2006 Elsevier B.V. All rights reserved.

Abstract: This paper presents dynamic thermal analyses of a p ower amplifier. All the investigations are based on the transient junction temperature measurements performed during the circuit cooling process. The presented results incl ude the cooling curves, the structure functions, the therma l time constant distribution and the Nyquist plot of the t hermal impedance. The experiments carried out demonstrated the influence of the contact resistance and the positio n of the entire cooling assembly on the obtained results.

Abstract: Polycrystalline electroceramics have been prepared by varying modifier to former (Bi/La) ratios () according to the complex formula Pb 092 [LaBi z ] 008 [Zr 065 Ti 035 ] 098 O 3 (PLBZT), where z = 00, 03, 06 The electrical properties of PLBZT compounds were studied using the ac impedance spectroscopy technique over a wide range of temperature (30–500 °C) in the frequency range of 100 Hz–1 MHz Nyquist plots recorded at different temperatures show a decrease in the bulk resistance ( R b ) with rise in temperature for PLZT material ( z = 00) ie, NTCR behavior like semiconductors The Nyquist plots also indicates that the bulk resistance of the material has been observed to be concentration dependent and decreased in two order of magnitude with higher Bi-addition in PLZT matrix Bismuth (Bi) substitution at the lanthanum (La) position not only resulted in lowering of the electrical resistance with its higher concentration but also has changed the NTCR behavior of PLZT ( z = 00) to PTCR (positive temperature coefficient of resistance) for PLBZT Electrical property studied by complex impedance spectroscopic method also indicates the evidence of (i) single electrical relaxation attributed to the presence of bulk contribution to the electrical properties, (ii) presence of temperature dependent electrical relaxation phenomenon and (i) diminution in the barrier to the mobility of charge carrier on Bi-substitution

Abstract: In an NMR measurement method using an NMR apparatus which converts a received signal to digital data using an analog/digital converter and performs a spectral analysis, a folding and aliasing count is decided from a variation in a peak frequency and frequency discrimination is performed. More specifically, a Nyquist frequency is changed to cause a variation of the peak frequency. Since the Nyquist frequency is inversely proportional to an increment of an evolution time t1 which is a feature of multi-dimensional NMR, the Nyquist frequency can be changed by changing the increment of the evolution time. Furthermore, the Nyquist frequency is changed in such a way that a ratio between different Nyquist frequencies is not a ratio between natural numbers n1 and n2 which are greater than 0 and smaller than or equal to the maximum folding and aliasing count.

Abstract: The corrosion behavior of X70 steel was studied by means of Tafel polarization,anodic linear potential sweep and EIS.With the increase of concentration of Na_2CO_3,the corrosion rate decreased firstly and then increased,while the corrosion potential increased firstly and then decreased.When the concentration of Na_2CO_3 was low,the Nyquist diagram was composed of a capacitive loop and an inductive loop.When the concentration of Na_2CO_3 was 0.1 mol/L,X70 steel began to be passivated,and the Nyquist diagram consisted of a single capacitive loop.When the concentration of Na_2CO_3 was higher,the capacitive loop became smaller,and the passivation was more difficult to occur.

Abstract: In an NMR measurement method using an NMR apparatus which converts a received signal to digital data using an analog/digital converter and performs a spectral analysis, a folding and aliasing count is decided from a variation in a peak frequency and frequency discrimination is performed. More specifically, a Nyquist frequency is changed to cause a variation of the peak frequency. Since the Nyquist frequency is inversely proportional to an increment of an evolution time t 1 which is a feature of multi-dimensional NMR, the Nyquist frequency can be changed by changing the increment of the evolution time. Furthermore, the Nyquist frequency is changed in such a way that a ratio between different Nyquist frequencies is not a ratio between natural numbers n 1 and n 2 which are greater than 0 and smaller than or equal to the maximum folding and aliasing count.

Abstract: The projection of the Nyquist Diagram of an SISO linear systems onto the Riemann sphere is recently used to represent the frequency responses. However, it is difficult to display the Riemann plot clearly in a plane since the Riemann sphere is a three dimensional object. To address this problem, the map projection of Riemann plot is introduced to obtain a two dimensional plot. The new frequency response plot plays the same role in modern robust control as Riemann plot, and easy to draw in a plane.

Abstract: The electrochemical reactions of carbon steel in LiBr solution have been investigated by electrochemical impedance spectroscopy. Inductive and capacitive loops were described in the Nyquist plots of electrochemical impedance at low and high frequency regions, respectively. On the basis of observation by confocal laser microscope, it was found that the localized corrosion site increased with the electrode potential, and that the dissolution rate of carbon steel increases with the increase of the localized corrosion. The electrochemical impedance spectra can be simulated with the empirical equation of the localized corrosion site and the electrode potential and equivalent circuit for the dissolution model of carbon steel.

Abstract: Polycrystalline sample of Pb2Bi3SmTi5O18, a member of tungsten–bronze (TB) family, was prepared using a high temperature solid state reaction technique. X-ray diffraction (XRD) analysis indicated the formation of a single phase orthorhombic structure. AC impedance plots were used as a tool to analyse the electrical behaviour of the sample as a function of frequency at different temperatures. The ac impedance studies revealed the presence of grain boundary effect, from 350°C onward. Complex impedance analysis indicated non-Debye type dielectric relaxation. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of Pb2Bi3SmTi5O18. AC conductivity data were used to evaluate the density of states at Fermi level and activation energy of the compound.

Abstract: This paper series presents detailed modeling and simulation studies of the nature of the impedance of solid oxide fuel cell (SOFC) anodes caused by gas-phase transport processes. The present part treats bulk gas-phase transport in button-cell experiments where gases are supplied from an outlet perpendicular to the electrode surface. This geometry is described using a stagnation point flow model based on the Navier-Stokes conservation equations, and the electrochemistry at the anode is modeled as global hydrogen oxidation using Butler-Volmer kinetics. These physical models account for the full nonlinear spatiotemporal coupling of gas phase diffusion, convection, and electrochemical kinetics. Polarization curves and impedance spectra are calculated through transient numerical simulation. Simulations are performed for various flow-field parameters, electrochemical rate laws, reference electrode placements, electrode polarization, gas phase compositions (H 2 /H 2 O/N 2 ), and temperatures. A strong and diverse influence of gas transport on impedance is predicted, including various shapes in the Nyquist plot and capacitive or inductive behavior. The study shows that in the bulk gas phase, diffusion and convection are closely coupled and cannot be separated in their impedance response. We propose description of these effects using the general term gas concentration impedance.

Abstract: Titanium and titanium-based alloys are employed widely in biomedical and dental applications. This is due to the stability and corrosion resistance exhibited by titanium, which is turn is due to the spontaneous formation of a passive titanium dioxide film, typically a few nm thick, which protects the metal from further oxidation. Electrochemical techniques viz., potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements were carried out to investigate the corrosion behavior of titanium and Ti-5Al-2Nb-1Ta alloy in simulated body fluid (SBF) solution. All the measurements were made in the simulated body fluid solution at different duration. Electrochemical impedance spectroscopic results were compared with those obtained by potentiodynamic polarization techniques. Impedance spectra were represented in both complex impedance diagram (Nyquist plot) and Bode plots. The impedance spectra were fitted using a non-linear least square (NLLS) fitting procedure. Double layer capacitance decreases with increase of charge transfer resistance of the titanium alloys studied.

Abstract: Co 3 O 4 -C composite powder has been synthesized via spray pyrolysis of cobalt nitrate-sugar solution at 600°C and assessed for application as anode materials in Li-ion batteries. Microstructural characterization by scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy confirm an even distribution of carbon throughout particles, as well as the presence of a carbon-based surface sheath surrounding Co 3 O 4 -C particle agglomerates. Charge-discharge cycling of half-cells indicates a stable reversible discharge capacity above 800 mAh g -1 . Equivalent circuit modeling of Nyquist plots show the Co 3 O 4 -C electrode has significant kinetic advantages over non-composite transition metal oxide electrodes.