Abstract: Poly(ethylene glycol) plasticized polymer electrolytes based on methyl cellulose have been prepared using the solution casting technique. Interactions between component materials in the electrolyte have been examined using Fourier transform infrared spectroscopy. The polymer-salt spectrum indicates that interaction occurred at the oxygen atom with the shift of the C–O stretching mode. Inference from the Nyquist plot suggests that the material can be represented by a resistor connected in series with a constant phase element. Capacitance evaluated from the fitting equation representing impedance of the equivalent circuit is observed to decrease with increasing temperature. From linear sweep voltammogram, the 63.75 wt% MC-21.25 wt% NH4NO3-15 wt% PEG, which is the highest conducting plasticized sample shows good electrochemical stability. This material has been tested as an electrolyte in electrical double-layer capacitor fabricated in this study. The electrochemical properties of the capacitors have been investigated by cyclic voltammetry, charge-discharge, and self-discharge characteristics. The discharge capacitance obtained is 38 F g−1.

Abstract: Lead-free perovskite (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT06) was prepared by conventional ceramic fabrication technique at 1160°C/3h in air atmosphere. The crystal structure, microstructure, dielectric, polarization, piezoelectric properties, and ac conductivity of the sample were studied. X-ray diffraction data confirmed the formation of a single phase tetragonal unit cell. Williamson-Hall plot was used to calculate the lattice strain and the apparent particle size. The experimental relative density of BNBT06 was found to be ~96-97% of the theoretical one with an average grain size ~4 μm. Room temperature dielectric constant and loss factor at 1 kHz were found to be equal to 781 and 0.085, respectively. Longitudinal piezoelectric charge coefficient of the poled sample under 2.5 kV/mm at 80°C in silicone bath was found to be equal to 124 pC/N. Complex impedance and electric modulus spectroscopic analyses showed the dielectric relaxation in the material to be of non-Debye type. The Nyquist plots and conductivity studies showed the NTCR character of BNBT06. The correlated barrier hopping model (CBHM) as well as jump relaxation model (JRM) was found to successfully explain the mechanism of charge transport in BNBT06. The ac conductivity data were used to evaluate the minimum hopping length, apparent activation energy, and density of states at Fermi level.

Abstract: We have studied sodium-ion conduction in complex hydrides NaAlH4 and Na3AlH6. The electrical conductivities of these complex hydrides were studied using ac impedance measurements at temperatures up to 363 K for NaAlH4 and 433 K for Na3AlH6. Nyquist plots obtained by the measurements indicated the sodium-ion conduction. Also, dc measurements showed that sodium-ion transference numbers of NaAlH4 and Na3AlH6 were almost unity. Na3AlH6 exhibited the sodium-ion conduction of 4.1 × 10−4 S/cm at 433 K. This study will open up research on complex hydrides as solid-state sodium-ion conductors.

Abstract: The polycrystalline sample of LiSr2Nb5O15 (LSN) was prepared by a high-temperature solid state reaction technique. The impedance parameters were studied using an impedance analyzer in a wide range of frequencies (10 2 -10 6 Hz) at different temperatures (28-500 ℃). Nyquist plot reveals the presence of bulk effect only. The bulk resistance of the compound decreases with rise in temperature which shows the negative temperature coefficient of resistance (NTCR) like a semiconductor. The ac conductivity spectrum was found to obey Jonscher's universal power law. DC conductivity (bulk) with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity and the activation energy found to be 0.97 eV.

Abstract: In this paper, we present two Sysquake interactive tools for the design of fractional-order proportional-int egral-derivative (FOPID) controllers. Therst tool deals with the time and frequency domain design of FOPID controllers, allowing the user to analyze the effects of changing user-chosen parameters. In the time domain, both set- point and load disturbance step responses of the control system are shown, as well as the effect of measurement noise. In the frequency domain, the Bode diagrams of all the most important closed-loop transfer functions are plotted. The second tool allows the user to determine automatically the controller parameters by applying a loop shaping technique, namely, by mapping a point of the process Nyquist plot to a target point of the loop transfer function Nyquist plot with a predened value of its derivative. In this context, constraints on the gain or phase margin or on the maximum sensitivity can be effectively considered. It is believed that this kind of Computer Aided Control System Design tools are very useful from an educational viewpoint and in allowing a widespread use of FOPID

Abstract: We show that a random walk model of diffused ions interprets well the experimentally deduced Nyquist plots in ionic chalcogenide glasses. Fitting of the model to the experimental data in the Nyquist plots of Ag–As–S(Se) glasses taken as case examples yields important physical parameters such as number of mobile Ag+ ions, hopping relaxation time and diffusion coefficient. It was found that the number of freely moving Ag+ ions is almost independent of Ag content in Agx (As0.33S(Se)0.67)100−x glasses, while the maximum hopping relaxation time is highly dependent on Ag concentration.

Abstract: Bismuth layered structure SrBi2Ta2O9 ceramic is prepared by the microwave sintering technique via solid state route at 1100°C for 30 mins. X-ray diffraction analysis is used to analyze the phase purity, which identifies the orthorhombic structure with A21am space group. The fracture surface of the sintered pellet is visualized by scanning electron microscopy. Impedance spectroscopy is used to analyze the sample behavior as a function of frequency and temperature. Impedance and modulus study reveals the temperature-dependent non-Debye type relaxation phenomenon. The Nyquist plot shows a single arc representing the grain effect in the material, and the conductivity increases with increase in temperature. The Nyquist plot is fitted with an equivalent circuit, and the simulated parameters are well agreed with the calculated parameters. Arrhenius plot shows two different activation energies at below and above 300°C which identifies the phase transition of SrBi2Ta2O9 ceramic. The fatigue property is explained by the basis of activation energies, which shows that SBT sintered by microwave technique is more fatigue resistant than conventional sintering.

Abstract: A simple and new point contact tungsten trioxide (WO3) sensor, which can be prepared by the oxidation of tungsten filaments via in-situ induction heating, likely detects low concentration (ppm level) environmental pollutants such as NO2. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were applied to characterize the phase and the microstructure of the samples, respectively. It was found that the synthesized WO3 films exhibited a monoclinic phase and were composed of hierarchical microcrystals and nanocrystals. The point contact WO3 sensor (W-WO3-W) showed rectifying characteristics and an ideal sensing performance of about 110°C. A single semicircle in Nyquist plots was recorded by electrochemical impedance spectroscopy (EIS) at a relatively low temperature of 150°C but faded away above 200°C, which revealed that the sensing process was governed by a determining factor, i.e., grain boundaries at the contact site.

Abstract: Polycrystalline sample of Ba5HoTi3V7O30 was prepared using solid-state reaction technique. X-ray structural analysis indicated a single-phase formation with orthorhombic structure. Microstructural study by SEM showed non-uniform distribution of grains over the surface of the sample. Impedance and modulus spectroscopy studies were carried out, as functions of frequency (42 Hz - 5 MHz) and temperature (RT-773K). The Nyquist plots clearly showed the presence of both bulk and grain boundary effect in the compound. Electrical phenomena in the material can appropriately be modeled in terms of an equivalent circuit with R, C and CPE in parallel. The fitting procedure used here allows us to determine the value of R and C with good precision. Here R2 and R3 correspond to the resistance contributed from the grain boundary and bulk, respectively. C1 and C2 correspond to the capacitance contributed from the grain boundary and bulk, respectively. The real part of electrical modulus shows that the material is highly capacitive. The asymmetric peak of the imaginary part of electric modulus M″, predicts a non Debye type relaxation. The activation energy of the compound (calculated both from impedance and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers.

Abstract: Two single crystals of the same ingot and a polycrystal with compositions close to CuIn2Te3.5, CuIn3Te5 and CuIn4Te6, respectively, have been studied using impedance spectroscopy at different temperatures in the 20–120 °C range. The negative imaginary impedance part, −Z**, as a function of the real impedance part, Z*, (Nyquist plots) can be fitted to one or two semicircles associated with the Warburg diffusion and related one or two mobile ions, depending on the slice composition. In dc current and using the current intensity decay method at 20 °C, the conductivity as a function of time permits one to compute the diffusion coefficients of one or two mobile ions observed in impedance spectroscopy. The diffusion coefficients of the Cu ion are higher than those in CuInSe2 and are associated with the number of copper vacancies, VCu, and indium–copper antisites, InCu, in the Cu sublattice. EDAX measurements in the slice profile, before and after the electrical analysis, confirm a massive motion of Cu atoms along the slice thickness. In all samples, there is a region with composition close to CuIn1.7Te3 and a new atomic distribution, different in each sample depending on the initial composition and their structure. The ionic motion permits one to understand the behaviour of chalcopyrite thin films when they are grown with a composition gradient (from a Cu-rich chalcopyrite to an In-rich one).

Abstract: SiO2–non-graphitizable carbon composites were prepared by pyrolysis of a mixture of ethyl cellulose and nano-sized SiO2. The composite electrode showed high reversibility in insertion and/or extraction reactions of Li ions at potentials below 1 V with little hysteresis after the 2nd cycle, whereas a large irreversible capacity was observed in the 1st cycle. This reversible capacity increased with increasing SiO2 content above 5 wt%. Li ion transfer at the interface between a composite electrode and an electrolyte was studied by ac impedance spectroscopy. In the Nyquist plots, a semi-circle that was assigned to charge-transfer resistance (Rct) because of Li ion transfer across the interface between the composite electrode and electrolyte appeared at potentials below 1 V. The values of Rct decreased with increasing SiO2 content. These results indicate that both a decrease in Rct and an increase in reversible capacity can be achieved by use of SiO2–non-graphitizable carbon composite electrodes; this would lead to Li-ion batteries with higher power and energy density.

Abstract: In this paper, an integrated servo-mechanical control systems design method using Nyquist plots is proposed for high-performance mechatronic systems. The proposed technique is used to analyze stability, performance, and robustness of the control system, considering control and mechanical specifications under one unified framework. The desired stability and performance specifications such as gain and phase margins, infinity norm of sensitivity transfer function, mechanical characteristics, and robustness against plant uncertainties, etc., are transformed into disc regions in the developed technique. The proposed methodology is used to design and analyze a control system for a voice coil motor actuated hard disk drive (HDD) targeted to provide stronger disturbance rejection capabilities on the identified critical resonant mode at 9,146 Hz. The designed controller is implemented in a commercial HDD, and experimental results show that the disturbance at the frequency of critical resonant mode is attenuated by ź7 dB for stronger vibration control.

Abstract: Proper design of metallized films capacitors requires an understanding of all parasitic parameters sources and their impacts on circuit operation. This paper presents a modeling approach based on the Nyquist diagram to identify different parameters of metallized films capacitors, and build an equivalent electrical circuit. Two types of capacitors have been evaluated and compared to validate the resulting model.

Abstract: The purpose of the current study is to simulate the behavior of a solid oxide fuel cell (SOFC) anode under sinusoidal excitation. The obtained harmonic response is used as a base for electrochemical impedance spectra simulation. The electrochemical impedance spectroscopy (EIS) is a powerful non-destructive tool for SOFC researches. In order to evaluate the EIS experimental results, efforts are devoted to develop EIS numerical simulation tools. In this study, a planar SOFC is modeled, and the steady state behavior and frequency response, as well as the electrochemical spectra of the anode, are obtained. The developed model couples the electrochemical kinetics with mass transport. The Butler–Volmer equation is used for the anode electrochemistry, and the species equations are used for gas transport in the anode channel. In order to solve the system of the nonlinear equations, an in-house code based on finite difference method is developed and utilized. A parametric study is also carried out, and the results are discussed. The simulation results are in good agreement with published data. Results show a capacitive semicircle in the Nyquist plot, which is identical to the gas diffusion impedance as reported in literatures.

Abstract: The polycrystalline Ba3Sr2GdTi3V7O30 material of tungsten bronze structural family was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction analysis exhibits the formation of single-phase compound with orthorhombic crystal system. Surface micrograph recorded by scanning electron microscopic (SEM) technique has well defined but non-uniformly distributed grains throughout the surface of the pellet sample. Detailed studies of dielectric properties as a function of temperature (306-773 K) and frequencies (10-10Hz) suggest that the compound has frequency independent diffused dielectric anomaly at a temperature ~620 K which may be related to ferroelectric phase transition which is confirmed from polarization study. The frequency and temperature dependence of impedance property of the material were analyzed using a complex impedance spectroscopy. The Nyquist plots confirmed the presence of grain and grain boundary effect in the material. Copyright © 2012 VBRI press.

Abstract: The electrical and dielectric properties of the compound C7H12N2[H2PO4]2 ⋅ 1/2H2O were investigated by the complex impedance spectroscopy, over a wide range of frequencies and temperatures, 600 Hz–5 MHz and 303–408 K, respectively. Besides, a detailed analysis of the impedance spectrum suggested that the electrical properties of the material at several temperatures and the electrical equivalent circuit have been proposed to explain the impedance results. Concerning the Nyquist plots, they clearly showed the presence of bulk and grain boundary. As for the imaginary part of modulus at several temperatures, it shows double relaxation peaks, thus suggesting the presence of grains and grain boundary conductions in the sample.

Abstract: Synchronous Nyquist folding receiver(SNYFR) is a new kind of interception architecture,which could simultaneously intercept wideband signals in multi-Nyquist zones with two analog-to-digital converters(ADCs).A parameter estimation algorithm is presented for the linear frequency modulated(LFM) signal intercepted by an SNYFR.First,taking the local oscillator signal(LOS) whose spectrum is symmetrical about the sampling rate as an example,the Nyquist zone does not exist under certain conditions.Second,the left sideband LOS SNYFR,whose zone does exist,is proposed.Then,the frequency decimation factor is designed as the modulated frequency of the sinusoidal frequency modulation(SFM) LOS to estimate the Nyquist zone.Finally,the under-sampled LFM signal is reconstructed by using the zone,and it is used to estimate the parameters of signal.Simulations show that all the parameter estimation accuracies are all close to Cramer-Rao lower bounds when the signal to noise ratio(SNR) is above 10dB.

Abstract: Stability analysis is one of the most important aspects to determine the performance of electric drive system during dynamic and steady state operating conditions. This is especially important since the motor operates in wide range of frequencies with the complex types of control strategies such as field oriented control and direct torque control. A new dynamic model is developed to study the instantaneous effect of varying voltage/current. In addition small signal equations are developed to evaluate the control performance by using conventional techniques such as Bode plot, Nyquist plot etc. In practice voltage-current relationships are used to perform such study. In this paper, the dynamic model based on voltage-flux-linkage relationship is utilized to evaluate the control performance of the three phase induction motor drive system. The presented model offers advantage of simplified analysis and provides more meaningful information. A study of voltage-current model and voltage-flux-linkage model has been carried out in this paper and important inferences are drawn from it. Analytical and simulation approach is used in the paper.

Abstract: We report the analysis of single-walled carbon nanotube networks, which are expected to be suitable as miniaturized flexible radio frequency RC filters and also have important implications for high frequency devices. The surface morphology obtained by atomic force microscopy shows that most of the growth on polypropylene carbonate substrate is homogeneous. The large value of peak intensity ratio of G and D band in Raman spectra indicates the high purity network. Nyquist plots of carbon nanotube networks on a flexible substrate are close to real circles, indicating that the material is conducting, and suggest a simple equivalent circuit having a resistor in parallel with a capacitor. The Bode plots give the dependence of real and imaginary impedances on frequency. While at high frequency, the impedance decreases, due to generation of capacitance between a single-walled carbon nanotube; at low frequency, it shows the normal behavior, having constant value. The tunnels among different carbon nanotubes are capable of storing electric charge. The accumulative capacitances of tunnels for three varied concentrations are calculated by electrochemical impedance spectroscopy simulations to fit the observed Nyquist plots.