Abstract: This article presents a fundamental and systematic investigation of NiO based p-type dye-sensitized solar cells (p-DSCs) using electrochemical impedance spectroscopy (EIS). The Nyquist plot features two semicircles. By varying the electrocatalytic properties of the counter electrode and the illumination intensities, we have unambiguously assigned the two semicircles to the charge transfer process at the counter electrode/electrolyte interface and the hole recombination at the NiO/dye/electrolyte interface, respectively. Key recombination parameters, including the recombination resistance, chemical capacitance, and the hole lifetime, have been obtained under illumination and in the dark. Comparisons between the recombination process of the typical n-DSCs and p-DSCs show that the hole lifetime in our NiO p-DSCs is shorter than the electron lifetime in the TiO2 n-DSCs under the same voltages.

Abstract: A new double perovskite oxide holmium cadmium titanate, Ho2CdTiO6 (HCT), prepared by solid state reaction technique is investigated by impedance spectroscopy in a temperature range 50–400°C and a frequency range 75 Hz–1 MHz. The crystal structure has been determined by powder X-ray diffraction which shows monoclinic phase at room temperature. An analysis of complex permittivity with frequency was carried out assuming a distribution of relaxation times as confirmed by Cole–Cole plot. The frequency dependent electrical data are analysed in the framework of conductivity and electric modulus formalisms. The frequencies corresponding to the maxima of the imaginary electric modulus at various temperatures are found to obey an Arrhenius law with an activation energy of 0·13 eV. The scaling behaviour of imaginary part of electric modulus suggests that the relaxation describes the same mechanism at various temperatures. Nyquist plots are drawn to identify an equivalent circuit and to know the bulk and interface contributions.

Abstract: High quality crednerite CuMnO2 was prepared by solid state reaction at 950 °C under argon flow. The oxide crystallizes in a monoclinically distorted delafossite structure associated to the static Jahn–Teller (J–T) effect of Mn3+ ion. Thermal analysis showed that it converts reversibly to spinel Cu x Mn3−x O4 at ~420 °C in air and further heating reform the crednerite above 940 °C. CuMnO2 is p-type, narrow semiconductor band gap with a direct optical gap of 1.31 eV. It exhibits a long-term chemical stability in basic medium (KOH 0.5 M), the semi logarithmic plot gave an exchange current density of 0.2 μA cm−2 and a corrosion potential of ~−0.1 VSCE. The electrochemical oxygen insertion/desinsertion is evidenced from the intensity–potential characteristics. The flat band potential (V fb = −0.26 VSCE) and the holes density (N A = 5.12 × 1018 cm−3) were determined, respectively, by extrapolating the curve C −2 versus the potential to the intersection with C −2 = 0 and from the slope of the Mott–Schottky plot. From photoelectrochemical measurements, the valence band formed from Cu-3d wave function is positioned at 5.24 ± 0.02 eV below vacuum. The Nyquist representation shows straight line in the high frequency range with an angle of 65° ascribed to Warburg impedance originating from oxygen intercalation and compatible with a system under mass transfer control. The electrochemical junction is modeled by an equivalent electrical circuit thanks to the Randles model.

Abstract: Electrochemical impedance spectroscopy (EIS) was employed to investigate diffusion of AlCl4- ions in basic (AlCl3-NaCl-KCl) molten salt. Nyquist plots in different DC offset potentials showed finite and restricted aluminum ion diffusion due to insertion and blocking in the graphite electrode. The general Warburg, open Warburg, and short Warburg impedance in the complex Nyquist plot of this system showed the anomalous diffusion behavior of the ions in the graphite electrode. The diffusion coefficient of the AlCl4- ions was calculated from the slope of the Warburg line in a totally blocking film in the graphite electrode and was found to be 2.8 \times 10-10 cm2/s.

Abstract: This work reports on the newly synthesized 9-tosyl-9H-carbazole (TsCz) monomer. Capacitive properties of the electrochemically grown homopolymer, poly(TsCz) film on carbon fibre microelectrode (CFME), are characterised by cyclic voltammetry (CV), Fourier transform infrared reflectance-attenuated total reflection spectroscopy (FTIR-ATR), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Different monomer concentrations (1, 3 and 10 mM) were used for electrodeposition in 0.1 M sodium perchlorate (NaClO4)/acetonitrile (ACN) solution. The capacitive behaviour of modified CFMEs was defined via Nyquist, Bode-magnitude and Bode-phase plots. An equivalent electrical circuit R(CR)(QR)(CR) for different concentrations of poly(TsCz)/CFME was proposed and experimental data were simulated to obtain the numerical values of the circuit components. The Nyquist plot for poly(TsCz) shows the highest specific capacitance (50.0 mF cm−2) at frequency of 0.01 Hz in the initial monomer concentration of 10 mM.

Abstract: A polycrystalline rare earth double perovskite oxide, strontium cerium niobate, Sr2CeNbO6 (SCN) is synthesized by solid state reaction technique for the first time. Impedance spectroscopy is employed to determine the electrical parameters (resistance (R), capacitance (C) and relaxation time (τ)) of SCN in a temperature range from 303 to 703 K and in a frequency range from 100 Hz to 1 MHz. The spectrum of imaginary part of complex impedance (Z″) at each temperature exhibits one relaxation peak. The modified Cole–Cole equation is used (experimental data is fitted with this model) to describe these relaxation peaks. Scaling behaviour of Z″ suggests that the relaxation describes the same mechanism at the entire temperature range. Impedance data of SCN that have capacitive and resistive components is represented by Nyquist diagram. The experimental impedance data is fitted using equivalent RC circuit at various temperatures. The grain conduction and τ follow an Arrhenius law associated with activation energy 0.87 and 0.88 eV, respectively.

Abstract: This paper presents two simple and effective methods to design problem of first- order controllers, having a transfer function of type G c (s)=k(1 + τ1s) (1+ τ 2 s), for a given linear plant possibly cascaded with a time-delay. These methods are based on dominant pole placement and use the root locus and Nyquist plot, respectively. Illustrative examples are given to demonstrate the effectiveness of the proposed methods.

Abstract: Low-to-medium-frequency range impedance spectroscopy was used to investigate two series of dried calcium silicate hydrates with or without aluminum atoms, C–S–H and C–A–S–H. Over four decades in frequency, sample Nyquist plots were fitted by adopting an equivalent circuit using constant phase elements (CPE). Conductivity values of the order of 10−9–10−10 S/cm were obtained at 316 K. The presence of CPE characteristic of the depleted semicircle at high frequency was related to a fractal dimension ranging from 2.4 up to 2.7. Above 316 K, the impedance spectra behaved unpredictably due to the dehydration process, while below 316 K the behavior was followed by adopting the modulus loss factor. The associated peak maximum variation is of the Arrhenius-type. The entire behavior may be interpreted by ionic motion and charge accumulation in addition to dielectric polarization at the grain boundaries associated to low fractal surface.

Abstract: The original relay feedback autotuning method of Astrom and Hagglund [1] is based on the Nyquist point at the phase angle of −π (the critical frequency). Recently, Friman and Waller [8] showed that the critical frequency is too high to tune PI controllers and proposed an autotuning method that finds a Nyquist point at the third quadrant through the two-channel relay. Here, the method to find Nyquist points in the third quadrant is revisited and adaptive relay feedback method which can be applied to noisy processes is proposed. It is shown that the bandwidths of PI control systems and the first-order plus time delay model identifications support the Nyquist point at the third quadrant. Nyquist points at the third quadrant can be obtained by introducing a filter and hysteresis to the relay feedback loop. However, the filter time constant and the size of hysteresis should be adjusted iteratively because their phase shifts are dependent on the resulting relay oscillation frequency. Simulations show that this adaptive relay feedback method finds a given Nyquist point at the third quadrant accurately under noisy environments and provides excellent PI control systems.

Abstract: Regenerated (FRF curves), synthesis of (FRF) curves there are two main requirement in the form of response model, The first being that of regenerating "Theoretical" curve for the frequency response function actually measured and analysis and the second being that of synthesising the other functions which were not measured,(FRF) that isolates the inherent dynamic properties of a mechanical structure. Experimental modal parameters (frequency, damping, and mode shape) are also obtained from a set of (FRF) measurements. The (FRF) describes the input-output relationship between two points on a structure as a function of frequency. Therefore, an (FRF) is actually defined between a single input DOF (point & direction), and a single output (DOF), although the FRF was previously defined as a ratio of the Fourier transforms of an output and input signal. In this paper we detection FRF curve using Nyquist plot under gyroscopic effect in revolving structure using computer smart office software. Keywords - FRF curve; modal test; Nyquist plot; software engineering; gyroscopic effect; smart office.

Abstract: A two-electrode probe was used for electrochemical impedance studies of hot corrosion kinetics of molybdenum-containing Ni3Al-base alloy IC6 covered with a solid Na2SO4 film at 750 and 800 °C in air. The alloy was subject to catastrophic corrosion at both temperatures, forming a thick porous oxide layer, as a result of the formation of Na2MoO4–MoO3–Na2SO4 melt. The experimental temperature affected the formation of the melt, the ionic conduction of the corrosion layer, and thus the impedance characteristics. For the corrosion at 800 °C the Nyquist plots were composed of two capacitive loops at high-mid frequency and a line at low frequency indicating a diffusion-controlled reaction. At 750 °C, however, the plots consisted of a single capacitive loop in the initial stage, followed by the same impedance features as at 800 °C. Two equivalent circuits were proposed to fit the impedance spectra at the two temperatures. Based on the precise measurements of diffusion impedance, the diffusion flux of oxygen through the salt layer was calculated, and the main reduction reaction was also discussed.

Abstract: A new approach for the robust fixed-order H ∞ controller design by convex optimization is proposed. In this paper, the robust performance condition is represented by a set of convex constraints with respect to the parameters of a linearly parameterized controller on the Nyquist diagram for prespecified frequency points. This method can directly handle frequency-domain uncertainty without any modeling. Frequency-domain uncertainty can be minimized by selecting the appropriate nominal plant model for the corresponding frequency points in the proposed method. The proposed method is compared with the standard H ∞ control by numerical simulation examples on a track-following control of a Hard Disk Drive.

Abstract: Analytical models for the acoustics of quarter wave resonators with temperature inhomogeneity are introduced in the form of impedance expressions. To study the effect of resonator rings on the axial propagation of transversal modes, a three dimensional, semi-analytical solution for the acoustic pressure distribution in cylindrical ducts with impedance shell boundary condition is then derived. Combining a low order network model approach with a Nyquist plot method, the linear stability of a thrust chamber is deduced. The main driving and damping mechanisms like mean flow, resonator ring, combustion and choked nozzle are considered. The stabilizing influence of the resonators is clearly observed.

Abstract: The invention discloses a method for judging the stability of a distributed power-supply system based on an equivalent open-loop transfer function. The method comprises the following steps: firstly, equivalently transforming a noise sensitivity transfer function of the system, on the basis of an equivalent two-port network characteristic of a source switch power supply, and deducing the equivalent open-loop transfer function shown in the description; and then respectively measuring port voltages v1(s) and v2(s) by connecting a small signal current source delta (s) to a connection bus of a converter, acquiring the equivalent open-loop transfer function shown in the description under the small signal disturbance, and drawing a Gop(s) nyquist diagram; and lastly, judging the stability of the system and forecasting the stability margin of the system according to the nyquist diagram. By using the method provided by the invention, the restraining terms of the original impedance ratio standard are extended. Besides, the method provided by the invention is easily realized and has important theoretic sense and application value in analyzing and designing the distributed power-supply system.

Abstract: Perovskite structured Na 0.5 Bi 0.5 TiO 3 (NBT) ceramics were synthesized by the solid-state sintering method. The presence of constituent phases and crystalline structure of the system was confirmed by X-ray diffraction technique exhibiting perovskite structure with rhombohedral symmetry. The dielectric behavior showed a broad peak at ∼400°C characterized as Curie temperature. The real part of impedance (Z′) as a function of frequency has higher values at lower frequencies and decreases up to 20 kHz and attains a constant value beyond that frequency. The broadening of peaks in frequency explicit plots of imaginary part of impedance (Z″) suggests that there is a spread of relaxation times, which involves more than two equilibrium portions. The purpose of giving dielectric data obtained from the impedance studies is to give the usefulness of the impedance formalism to evaluate the dielectric behavior in the present sample. The Nyquist plot and conductivity studies showed the NTCR character of NBT ceramic samples.

Abstract: Introduction To keep ahead of the rapid developments in mechanical, electrical, and computational techniques used in modern mechatronic systems, continual improvements in control systems design are essential. In this paper, we propose an analytical tool using Nyquist plots and the Circle Criterion [1] to facilitate the integrated control design for highperformance mechatronic systems. Our proposed technique provides great convenience to analyze all the critical information of the control system under consideration in one graph. The desired stability and performance specifications such as gain and phase margins, infinity norm of sensitivity transfer function, plant characteristics, and robustness against plant uncertainties, etc., can be transformed to disc region in the developed technique.

Abstract: PROBLEM TO BE SOLVED: To prevent a shape of a Nyquist plot obtained from a circuit model from being accidentally matched with a shape of an actually measured Nyquist plot, by allocating frequency ranges to unit circuits constituting the circuit model to perform fitting.SOLUTION: A device for evaluating battery characteristics includes: an impedance measuring means; a plot means for creating a Nyquist plot in which a real number component and an imaginary number component of impedance are plotted; a circuit model creation means for creating a circuit model of a battery on the basis of the Nyquist plot; a frequency allocation means for allocating frequency ranges to a plurality of unit circuits respectively; a fitting means for finding electrical characteristic values of elements constituting the unit circuits on the basis of the allocated frequency ranges; and a determination means which creates a Nyquist plot of the circuit model on the basis of the electrical characteristic values, which are found by fitting, of the elements constituting the unit circuits and compares this Nyquist plot with the Nyquist plot created by the plot means to determine validity of the circuit model.

Abstract: In the present work, the effect of partial substitution of titanium by tungsten has been investigated. X-ray diffractograms confirm the formation of single phase pervoskite structure. SEM micrograph shows randomly distributed grains in the sample. Variations of dielectric constant with temperature at different frequencies show that compounds undergo a ferroelectric to paraelectric phase transition at 296 K. A well defined hysteresis loop is formed at room temperature. Variation of dielectric loss with temperature at different frequencies shows a decrease in loss with increasing frequency. The Nyquist plots (Cole–Cole plots) were plotted at temperatures 285°C, 310°C and 335°C. The variation of dc conductivity as a function of temperature has also been studied.

Abstract: Two types of activated carbons were produced by chemical activation respectively with and without pre-carbonization procedure, and were used in organic electrolyte supercapacitors. Galvanostatic charge and discharge results show that voltage upper limit and activated carbon type obviously influence the cycle stability of the capacitors. And cyclic voltammograms reveal the better capacitive behavior and cycle stability of the activated carbon produced with carbonization procedure implying the correlation between these two factors. While Nyquist plots disclose the tendency of equivalent circuit component parameters and electrode processes with cycling.

Abstract: ZnO is a wide band gap semiconductor with many applications such as in solar cells, varistors, and other electrical components. The ZnO material was synthesized using a sol-gel method. The material was characterized using X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The material is pure and single phase. Electron conduction in ZnO nanomaterials was done using alternating current (ac) impedance. The frequency ranges of the measurements used were 1x 10-3 Hz to 1x 106 Hz and the ac impedance measurements were done within a temperature range of 60oC to 100oC. Nyquist plots were drawn and bulk resistances were obtained. Subsequently, conductivity values were calculated and the diffusion characteristics were obtained. From further analysis of the conductivities with temperature, the diffusion of electrons in the material was studied. It was found that the conductivity increased with the increase of temperature which meant that the rate of diffusion of the electrons through the materials also increased. An Arrhenius relation was concluded for the electron diffusion in the ZnO nanomaterials.

Abstract: A new approach for the robust fixed-order H ∞ controller design by convex optimization is proposed. In this paper, the robust performance condition is represented by a set of convex constraints with respect to the parameters of a linearly parameterized controller on the Nyquist diagram for prespecified frequency points. This method can directly handle frequency-domain uncertainty without any modeling. Frequency-domain uncertainty can be minimized by selecting the appropriate nominal plant model for the corresponding frequency points in the proposed method. The proposed method is compared with the standard H ∞ control problem by experiments.

Abstract: The polycrystalline sample of KPb2V5 O15 was prepared by a mixed-oxide method relatively at low temperature (i.e., 550°C). X-ray diffraction studies of the compound showed the formation of single phase orthorhombic crystal structure at room temperature. SEM micrograph showed the homogeneous distribution of grains throughout the sample. Electric properties were analyzed using the complex impedance spectroscopy. The modulus plot showed the presence of both the grain and grain boundary effect. The bulk impedance evaluated from the Nyquist plots was observed to decrease with the rise in temperature, showing a negative temperature coefficient of resistance. The variation of AC electrical conductivity (σAC) was measured in a wide temperature (30–500°C) and frequency (102–106 Hz) range. The activation energy of the compound calculated from both the impedance and modulus spectrum was found to be the same.