Abstract: The classical relay feedback method for tuning proportional-integral-derivative (PID) controllers cannot be applied to plants whose Nyquist diagrams do not cross the negative real axis; these are customarily tuned based on the reaction curve experiment. In this brief, we propose a tuning method based on a modified relay feedback experiment. In this experiment, a transfer function of constant phase in an arbitrarily large range of frequencies is inserted in the loop. The proposed methodology thus unifies the Ziegler-Nichols-like tuning methods, by allowing PID tuning based on relay feedback for a class of plants without ultimate frequency.

Abstract: Nickel oxide nanoparticles were synthesized using low cost sol-gel method. The structure of as prepared NiO nanoparticles has been confirmed from X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray (SEM and EDX) spectroscopic analysis. The electrical and dielectric properties were characterized by complex impedance spectroscopy as a function of frequency at different temperatures. To study the dielectric behavior of the nanoparticles different plots like Nyquist plot, modulus plot and Bode plot were used. Also the frequency dependent ac conductivity is analyzed and the activation energy is calculated. The dielectric constant and dielectric loss as a function of frequency at various temperatures are also studied.

Abstract: We have investigated the structure and the electrical properties of CoFe2O4, Ni0.5Co0.5Fe2O4 and Zn0.5Co0.5Fe2O4 nanoparticles, prepared through a chemical pyrophoric reaction technique. The study of the dielectric constant reveals evidence of Rabinkin and Novikova polarisation in the system. The increased value of the dielectric constant at low frequency is attributed to the presence of interfacial and dipolar polarisation in the system. The impedance for Zn0.5Co0.5Fe2O4 nanoparticles is found to decrease with increase in temperature, indicating the presence of a temperature-dependent electrical relaxation process in the system. Nyquist plots have been fitted using parallel combinations of grain boundaries resistance and grain boundaries capacitance. The activation energy is estimated from Nyquist plots, dc and ac conductivity data using the Arrhenius relation. This is indicating that the same type of charge carrier is responsible for the relaxation and the conduction processes in the system. Ac ...

Abstract: In this work, nanostructure FeMnO3 perovskite material was synthesis by sol–gel auto combustion method using the glycine as a chelating agent for the first time in the literature. The synthesized materials were investigated structural, electrical, and magnetic properties by various characterization techniques. The X-ray diffraction reveals that the density and specific surface value are 2.54 g/cm3 and 1.468 m2/g, respectively. FE-SEM investigated surface morphology in the nanoscale region. The FeMnO3 material is existing antiferromagnetism at room temperature. Electrical property such as dielectric constant, tangent loss, and impedance spectrum, Nyquist plot with an equivalent circuit, AC conductivity, and electric modulus was analysed. The real part of permittivity, dielectric tangent loss with varying with temperature shows that the behaviour of Maxwell–Wagner relaxation in the FeMnO3 might be observed oxygen vacancy. The Nyquist plot gives more information-related electrical conduction process and individual contribution of grain and grain boundaries. The resistance (Ω) and capacitance (farads) values are varied with increasing temperature. An electric modulus value is varied under suppression electrode polarization and shows the effect of bulk and grain boundaries.

Abstract: The electrical and dielectric properties of PVA/Mg[ClO4]2 hybrid films were investigated in the temperature range of 90–150 °C and the frequency range of 20 Hz–10 MHz using impedance and modulus spectroscopy. Impedance and modulus analyses had indicated the temperature independent distribution of relaxation times and the non-Debye behavior in these composites. The co-operative motion due to strong coupling between the mobile Mg2+ ions is assumed to give rise to non-Debye type of relaxation. Complex impedance Nyquist plots are used to interpret the relaxation mechanism. The nature of Nyquist plot confirms the presence of bulk effects, grain boundaries and electrolyte/electrode polarization, and non-Debye type of relaxation processes occurs in the composites. A thermally activated relaxation was observed, which was ascribed to be a non-Debye-type relaxation caused by the mobility of magnesium ion in polymer matrix. A comparison between Z″, imaginary part of complex impedance, and M″, imaginary part of complex electric modulus, indicates that the short- and long-range charge motion dominates at low and high temperatures, respectively. The activation energies, which were obtained from the electric modulus and bulk conductivity, are matched well. The non-coincidence of peaks corresponding to the modulus and impedance indicates deviation from Debye-type relaxation.

Abstract: The substituted pyrochlore La 1.9 Ba 0.1 Sn 2 O 7 was prepared by nitrate route and the physical and electrochemical characterizations were investigated. The optical gap is found to be 3.01 eV and the conductivity is characteristic of a semiconducting behavior with activation energy of 0.42 eV. The conduction band of La 1.9 Ba 0.1 Sn 2 O 7 (−2.64 V SCE ), predicted from electro negativities of the constituent atoms, is close to that determined experimentally (−2.99 V SCE ). The capacitance measurement (C −2 –V) exhibits a linear behavior, characteristic of p type conductivity, from which a flat band potential of −0.05 V SCE and hole density N D of 8.42 × 10 14 cm −3 were determined, in agreement with the small electrical conductivity (σ 300K ∼3 × 10 −6 Ω −1 cm −1 ). The Nyquist plot showed a semicircle which is a contribution of capacitance and resistance in parallel. A bulk resistance contribution (R b = 71 kΩ cm 2 ) and a low density of surface states are observed. The center of the arc is localized below the real axis with a depletion angle of 14° ascribed to a constant phase element (CPE). As application, chromate was successfully converted to Cr 3+ on the pyrochlore under sunlight. ∼1 h was necessary to reach the adsorption equilibrium for an initial chromate concentration of 10 −4 M. The conduction band is more cathodic than the potential of HCrO 4 − which is spontaneously reduced under solar light. The best performance is obtained at pH ∼ 3 with a catalyst dose of 1 mg/mL. 40% of chromate disappears with a quantum yield of 0.53% in less than 2 h. The process obeys to a first order kinetic with an apparent rate constant of 2.3 × 10 −3 min −1 .

Abstract: A highly sensitive impedance sensor operating at room temperature has been developed for the quantitative determination of formaldehyde vapor. Nanostructured zinc oxide (ZnO) was synthesized by chemical reduction and used, in the form of a pellet, as the sensing material. Its performance was compared to that of the pellet made from commercial ZnO. Both samples were characterized by X-ray diffraction, Fourier transform infra-red spectroscopy, ultraviolet–visible spectroscopy, and atomic force microscopy techniques. Changes in impedance caused by formaldehyde in the concentration range from 100 to 800 ppm were measured and Nyquist plots revealed a systematic variation in impedance. The sensor response and formaldehyde concentration are exponentially correlated for both the laboratory synthesized and commercial ZnO samples. However, the lab-synthesized sample displays a better performance in terms of sensitivity, response, recovery, and stability. In addition, the response of the lab-synthesized sample is less sensitive to interferences by reducing gases such as ammonia, ethanol, methanol, and propanol.

Abstract: Present work deals with a two-step synthesis and electrochemical properties of nickel oxide @copper oxide@copper (NiO@CuO@Cu) bilayered electrode. In the first step, anodization (40 V for 25 min) of Cu foil has been carried out for forming Cu-hydroxide@Cu which when annealed at 300 °C for 1 h produces CuO@Cu. In the second step, Ni-hydroxide is deposited onto CuO@Cu by applying current density of 0.03 A/cm2 for 3 min which when re-annealed at 300 °C for 1 h gives out NiO@CuO@Cu bilayered electrode. Obtained NiO@CuO@Cu bilayered electrode demonstrates separate CuO and NiO phases. The electrochemical properties have obtained using cyclic voltammetry, galvonostatic charge-discharge, and Nyquist plot measurements that reveal an importance of NiO@CuO@Cu as a potential electrode material in the electrochemical supercapacitor application with 58.14, 51.25, and 4.73 F g−1 values in 0.5 M, NaOH, KOH, and Na2SO4 electrolytes, respectively, measured at 2 mVs−1 scan rate.

Abstract: The optical and electrical characteristics of a graphene oxide solution (GS) with different graphene oxide (GO) concentrations in de-ionized water are investigated via the electrochemical impedance spectroscopy (EIS) method. The measurement results produced by the EIS for the GS are represented with both Bode and Nyquist plots in a frequency range from 1 kHz to 10 MHz. Using these results, we develop an equivalent circuit model as a function of the GO concentration, representing the GS as a mixed circuit of two-dimensional (2D) GO dispersed in parallel in de-ionized (DI) water. The underlying physics of the current-flowing behavior in the GS are explained and interpreted using empirical circuit models; the circuit model also shows that highly resistive GO becomes conductive in GS form in the DI water. The findings in this work should draw new attention toward GSes and related applications, including functional composite materials, catalysts, and filter membranes.

Abstract: This paper is focused on the dynamic modelling of the polycrystalline silicon wafer-based photovoltaic cells under various operational and fault conditions. The models are drawn from the impedance changes observed using electrochemical impedance spectroscopy. In this paper, tests were carried out at different voltage bias levels under illumination, dark, uniform partial shading, and cell-mismatch conditions. The cell model parameters are extracted from the obtained Nyquist plots and fitted to appropriate equivalent circuits. Results obtained show that, the variations of the AC model parameters can be used for in-line characterization and real-time condition monitoring of the photovoltaic cells/arrays under the different operational and fault conditions.

Abstract: The capacitive behavior of the hydrophobic fluorinated polymeric ionic liquid, poly[2-(methacryloyloxy)ethyl]-trimethyl ammonium nonafluoro-1-butanesulfonate (poly-IL), has been investigated by current-voltage (C-V) measurements and electrochemical impedance spectroscopy (EIS) using a cell featured by a ITO/poly-IL/Al sandwich structure. The data were collected in the temperature range between 30 and 60 °C. The Nyquist plot shows a slope variation that indicates a moderate increasing of the ions mobility with temperature. The Bode diagram reveals that the sample exhibits a capacitive behavior below 104 Hz with no redox processes at the electrodes as confirmed by the C–V curves. The material shows a relatively high thermal stability, probably due to its polymeric nature making the capacitor almost insensitive to the variation of the operating temperature.

Abstract: Impedance spectroscopy is a popular analytical tool in materials research and gives plenty of information after careful analysis. Experimentally obtained data can be analyzed by using a mathematical model based on possible physical theory that predicts theoretical impedance or a relatively empirical equivalent circuit. In the present review the complex impedance plots, i.e. Nyquist plots are analyzed by Z-view software and the values of grain and grain boundary resistances and capacitances are evaluated and the equivalent circuits are proposed for different materials. The results of pure and doped lead tartrate crystals, pure and amino acid doped ADP crystals and pure Hydroxyapatite nano-particles are reviewed. It has found that grain and grain boundary effects are very sensitive to doping and it is reflected in Nyquist plots. From the results it is found that the impedance spectroscopy technique is a sensitive technique to detect impure or doped system.

Abstract: Evaluating a set of coefficients of a PID controller that stabilises a given plant is an important topic in designing such a controller. In the literature, the stability boundaries of the coefficients are already computed in the k P –k I –k D space. However, in the existing methods, one of the coefficients must be swept to compute the stable regions in the plane of the two other coefficients. A novel method is presented to compute the regions in the plane of two controller coefficients such that some stable interval exists for the third coefficient. Therefore, the stability crossing boundaries are no longer required to be computed. The main idea used here is to compute the controller coefficients where the Nyquist plot gets tangent to the real axis and the values where the plot has self-intersections on the real axis. This leads to the main contribution of the study that eliminates the need to sweep the proportional coefficient to plot the stability domains in the k I/k P-k D/k P plane.

Abstract: The Na x Li1-x CdVO4 (x = 0.5, 1) orthovanadates were prepared using a solid-state reaction method. The x-ray diffraction patterns (XRDP) of both materials reveal the formation of the Na2CrO4 structure. Vibrational study confirms the existence of [VO4]3− group. Electrical measurements of our compounds have been investigated using complex impedance spectroscopy (CIS) in the frequency and temperature range 209 Hz–1 MHz and 589–703 K, respectively. Nyquist plots reveal the presence of tow contributions, an equivalent circuit was proposed. DC conductivity shows electrical conduction in the material as a thermally activated process. The AC conductivity is explained using the non-overlapping small polaron tunneling (NSPT) conduction mechanism. A relationship between crystal structure and ionic conductivity was established and discussed.

Abstract: The aim of this work is the study of dielectric and electrical performance of a dielectric anionic clay based on copper and chromium, and intercalated by chloride ions. Dielectric was synthesized by soft chemistry using the coprecipitation method at room temperature. The analysis of physicochemical properties of the material is performed by X-ray diffraction, Fourier transform-infrared, thermogravimetric analysis, and inductively coupled plasma.As for the dielectric response, it was performed using the dielectric impedance spectroscopy. Two relaxation modes were detected at the Nyquist diagrams. Modelization with equivalent circuit allowed us to determinate intrinsic electrical parameters of the dielectric (resistance, capacity) corresponding to the two contributions. The evolution of the dielectric constant with the frequency gave values comparable to the dielectrics. Finally, an adjustment according to Jonscher law was developed to determine the value of residual conductivity generally present i...

Abstract: The basic approaches of parametric analysis of impedance measuring front-end on the base of SPICE modeling are considered in paper. The method for impedance analysis using the mathematical functions of real Re and imaginary Im signal components is applied. By means of this functions it is possible to investigate the frequency dependences of the corresponding values of the active ReZ and the reactive ImZ impedance, and, thus, to plot the Nyquist diagram. In this article, the galvanostatic measurement method is used, which is on the base of the determination of the ratio and phase delay between the voltage and the harmonic current with the specified amplitude and frequency. As a result of simulation, the possibility of significant increase of the measurement transformation accuracy is found by means of modifying the input circuits of the impedance measuring front-end.

Abstract: An interactive graphical method of design is proposed in order to design a system which is robust and ultrafast. The aim will be to design a compensator with specific sensitivity bound e on a given bandwidth while not exceeding a global sensitivity value M at all frequencies. The Geogebra program allows to adjust the compensator so that the open loop Nyquist plot is tangential to the M sensitivity circle at all frequencies, while staying outside the sensitivity circle e within the designated bandwidth. The design is based on an improved quasi linear controller, i.e. a controller in which the high frequency cut-off depends on the open loop gain. The design also aims at keeping the Nyquist plot as close to the real value line −1/2 on the Nyquist plane so as to ensure a closed loop gain of unity on a maximum range of frequencies. The compensator is tuned with phase networks whose effects are seen graphically. The compensator's parameters are chosen so as to minimize the settling time of the time response.

Abstract: LaFeO3 is a material with Perovskite structure which electrical properties got investigated a lot, because as a p-type semiconductor it showed good gas sensing behavior through resistivity comparison. Sr doping on LaFeO3 is able to improve the electrical conductivity through structural modification. Using the Sr atoms doping concentration (x) from 0.1 to 0.4, La1-xSrxFeO3 nanocrystal pellets were synthesized using sol-gel method, followed by gradual heat treatment and uniaxial compaction. Structural analysis from XRD characterization shows that the structure of the materials is Orthorhombic Perovskite. The topography of the sample by SEM reveals grain and grain boundary existence with emerging agglomeration. The electrical properties of the material, as functions of frequency, were measured by Impedance Spectroscopy method using RLC meter. Through the Nyquist plot and Bode plot, the electrical conductivity of La1-xSrxFeO3 is contributed by grain and grain boundaries. It is reported that La0.6Sr0.4FeO3 sam...