Step Voltage Excitation Research Articles

Self-Organized Memristive Ensembles of Nanoparticles Below the Percolation Threshold: Switching Dynamics and Phase Field Description.

Percolative memristive networks based on self-organized ensembles of silver and gold nanoparticles are synthesized and investigated. Using cyclic voltammetry, pulse and step voltage excitations, we study switching between memristive and capacitive states below the percolation threshold. The resulting systems demonstrate scale-free (self-similar) temporal dynamics, long-term correlations, and synaptic plasticity. The observed plasticity can be manipulated in a controlled manner. The simplified stochastic model of resistance dynamics in memristive networks is testified. A phase field model based on the Cahn-Hilliard and Ginzburg-Landau equations is proposed to describe the dynamics of a self-organized network during the dissolution of filaments.

Size-dependent nonlinear vibration analysis of shear deformable microarches using strain gradient theory

Non-classical continuum theories are able to capture the size-dependent behavior of microscale structures. Among them, strain gradient modeling is one of the most accurate ones. The objective of this paper is to develop for the first time a nonlinear strain gradient formulation for the vibrational analysis of electrostatically actuated shear deformable microarches. The normalized equations of motion and the corresponding boundary conditions are derived based on Hamilton’s principle. Novel closed form expressions are derived for the mode shapes of the system using the perturbation technique. These mode shapes are then utilized in a Galerkin projection method to reduce the partial differential equations of motion to time domain nonlinear ordinary differential equations. Multiple time scales perturbation technique is then employed to derive analytical solutions for the nonlinear vibration of the system resulting from a DC step voltage excitation. The analytical results are compared with numerical simulations, and excellent agreement is observed. The formulations and the results presented in this paper can be utilized for design, analysis and synthesis of microscale bistable structures with pre-deformed thick microbeams as their main operating element.

Revisiting the Curie-Von Schweidler Law for Dielectric Relaxation and Derivation of Distribution Function for Relaxation Rates as Zipf’s Power Law and Manifestation of Fractional Differential Equation for Capacitor

The classical power law relaxation, i.e. relaxation of current with inverse of power of time for a step-voltage excitation to dielectric—as popularly known as Curie-von Schweidler law is empirically derived and is observed in several relaxation experiments on various dielectrics studies since late 19th Century. This relaxation law is also regarded as “universal-law” for dielectric relaxations; and is also termed as power law. This empirical Curie-von Schewidler relaxation law is then used to derive fractional differential equations describing constituent expression for capacitor. In this paper, we give simple mathematical treatment to derive the distribution of relaxation rates of this Curie-von Schweidler law, and show that the relaxation rate follows Zipf’s power law distribution. We also show the method developed here give Zipfian power law distribution for relaxing time constants. Then we will show however mathematically correct this may be, but physical interpretation from the obtained time constants distribution are contradictory to the Zipfian rate relaxation distribution. In this paper, we develop possible explanation that as to why Zipfian distribution of relaxation rates appears for Curie-von Schweidler Law, and relate this law to time variant rate of relaxation. In this paper, we derive appearance of fractional derivative while using Zipfian power law distribution that gives notion of scale dependent relaxation rate function for Curie-von Schweidler relaxation phenomena. This paper gives analytical approach to get insight of a non-Debye relaxation and gives a new treatment to especially much used empirical Curie-von Schweidler (universal) relaxation law.

Detection of questionable occlusal carious lesions using an electrical bioimpedance method with fractional electrical model.

This in vitro study evaluated the diagnostic performance of an alternative electric bioimpedance spectroscopy technique (BIS-STEP) detect questionable occlusal carious lesions. Six specialists carried out the visual (V), radiography (R), and combined (VR) exams of 57 sound or non-cavitated occlusal carious lesion teeth classifying the occlusal surfaces in sound surface (H), enamel caries (EC), and dentinal caries (DC). Measurements were based on the current response to a step voltage excitation (BIS-STEP). A fractional electrical model was used to predict the current response in the time domain and to estimate the model parameters: Rs and Rp (resistive parameters), and C and α (fractional parameters). Histological analysis showed caries prevalence of 33.3% being 15.8% hidden caries. Combined examination obtained the best traditional diagnostic results with specificity = 59.0%, sensitivity = 70.9%, and accuracy = 60.8%. There were statistically significant differences in bioimpedance parameters between the H and EC groups (p = 0.016) and between the H and DC groups (Rs, p = 0.006; Rp, p = 0.022, and α, p = 0.041). Using a suitable threshold for the Rs, we obtained specificity = 60.7%, sensitivity = 77.9%, accuracy = 73.2%, and 100% of detection for deep lesions. It can be concluded that BIS-STEP method could be an important tool to improve the detection and management of occlusal non-cavitated primary caries and pigmented sites.

Memcapacitor response under step and sinusoidal voltage excitations

Recently, mem-elements have become fundamental in the circuit theory through promising potential applications based on the built-in memory-properties of these elements. In this paper, the mathematical analysis of the memcapacitor model is derived and the effect of different voltage excitation signals is studied for the linear dopant model. General closed form expressions and analyses are presented to describe the memcapacitor behavior under DC step and sinusoidal voltage excitations. Furthermore, the step and sinusoidal responses are used to analyze the memcapacitor response under any periodic signal using Fourier series expansion where the effect of the DC component on the output response is investigated. In addition, the stored energy in the memcapacitor under step, sinusoidal and square wave excitations is discussed. Moreover, the analysis of series and parallel connection of N non-matched memcapacitors in general is introduced and special cases of matched memcapacitors are discussed. The derived equations are verified using SPICE simulations showing great matching.

Field measurement and simulation of electromagnetic transients on 132 kV oil-filled submarine cables

High-voltage cables with paper-oil based insulation are still widely used in electric power systems. One issue with EMTP-type modeling and simulation of such cables is that the permittivity of the insulation is frequency-dependent, thereby contributing to the dispersion of traveling waves. This frequency dependency is not taken into account in currently available EMTP-type programs. This paper presents field measurements from step voltage excitations on three different oil-filled cables with steel armoring. The waveforms are compared to EMTP-type simulations, demonstrating significant deviations from the measured waveforms. The frequency-dependency of the permittivity is next taken into account using a formula obtained by Breien and Johansen, and the modeling and simulation procedure is repeated. Inclusion of the frequency-dependency is shown to bring the simulation results much closer to the measured waveforms.

Study of Transformer Resonant Overvoltages Caused by Cable-Transformer High-Frequency Interaction

Power transformers can fail from dielectric stresses caused by electromagnetic transients. In this paper, we focus on a special phenomenon where excessive overvoltages arise due to resonance. This situation can take place when a transformer on the high-voltage side is connected to a cable and the low-voltage side is unloaded. Very high overvoltages can then result on the low-voltage side from transient events that cause a weakly attenuated overvoltage on the cable with a dominant frequency matching a resonance peak in the transformer voltage ratio. Laboratory tests on a 11-kV/230 V distribution transformer show that a step voltage excitation on a 27-m cable produces 24-p.u. overvoltage on the open low-voltage side. The voltage waveforms are accurately reproduced by a black-box model obtained from frequency sweep measurements. Simulations show that overvoltages as high as 43 p.u. could occur with the most unfavorable cable length. It is further shown that the following situations can lead to high overvoltages on an unloaded transformer low-voltage side: 1) ground fault initiation at the far cable end, 2) cable energization from a busbar with several other cables connected, 3) cable energization from another cable with the same length, and 4) capacitor bank energization at the far cable end.

Knee bioelectric impedance assessment in healthy/with osteoarthritis subjects

The present study analyzes parameters estimated by bioelectric impedance spectroscopy (BIS) in subjects with healthy and with osteoarthritis (OA) knees. Thirty-two male volunteers, members of the Parachute Military Infantry Brigade of Rio de Janeiro, Brazil, participated in the study (62 knee joints). Clinical specialists used the Dejour scale for OA classification and divided the subjects into a control (without OA) and a pathological group (with different degrees of OA). BIS data were obtained in a standing position using a BIS technique based on the current response to a step voltage excitation. Differences between groups were measured by means of a Wilcoxon–Mann–Whitney test. Results indicate that raw bioimpedance parameters seem to be sensitive to the physiological changes associated with OA. Thus, data indicate that extra-cellular resistance (Re) and reactance of the equivalent capacitance (Xcx) increase according to the disease intensity (p < 0.001). In conclusion, the BIS technique seems to be able to provide the objective and non-invasive basis for helping the diagnosis of knee OA.

Measurement of viscosities from the transient current of nematic liquid crystals with negative dielectric anisotropy

A method for measuring the complete set of the Leslie viscosity coefficients of nematic liquid crystals (NLCs) with negative dielectric anisotropy (Δ ε < 0) is proposed. The method is based on the analysis of the transient current, induced by step voltage excitation, in homeotropic NLC cells. It has been shown that the transient current in homeotropic NLC cells with Δ ε < 0 can be explained by the theory of NLCs in which the flow effects and the free-slip boundary condition are taken into account [Y. Iwata et al., Jpn. J. Appl. Phys. 43 (2004) L 1588]. It is demonstrated that the complete set of the Leslie viscosity coefficients of NLCs with Δ ε < 0 can be simultaneously and accurately measured by fitting the transient current calculated by the theory to the experimental data with a differential correction method.

Slow Dielectric Relaxation in Pb(Zr,Ti)O3 and (Ba,Sr)TiO3 Ferroelectric Thin Films

An impedance analysis of Ni/Pb(Zr,Ti)O3/Pt thin-film structures based on measurements at the frequencies from 100 Hz to 100 MHz, along with the data of Grazing Angles XRD, TEM and photo-electric study, is used to obtain electronic structure of the PZT thin films deposited by sol-gel method on silicone substrates. Both slow capacitance relaxation and charging/discharging currents versus time under step-voltage excitation have been studied in (Ba,Sr)TiO3 thin films between SrRuO3 electrodes.

Transient electroluminescence of single and multilayer organic light emitting devices

The transient current and electroluminescence response induced by a positive step voltage excitation in both single layer NPB and bi-layer NPB–Alq 3 devices were analyzed in detail. The transport of hole and electron in single NPB layer and bi-layer NPB–Alq 3 devices was investigated, respectively. The hole mobility was measured to be (1–3)×10 −4 cm 2 V −1 s −1 in NPB, while the electron mobility in the NPB–Alq 3 device was measured to be (4–8)×10 −6 cm 2 V −1 s −1. The charge transport delay time in each layer of the bi-layer structure was resolved from the transient current characteristics for voltage pulse amplitude near the turn-on voltage of the device. Such unique measurements applied to the organic bi-layer structures revealed the dynamics of the charge carriers, particularly in terms of the field-dependent mobility.

Transient analysis of microwave active circuits based on time-domain characteristic models

A modular method is presented to speed up transient simulation of microwave active circuits which consist of linear components and active devices that are often nonlinear. Firstly, the linear components and active devices are individually characterized by time-domain characteristic models (TDCM's) and lumped equivalent circuits, respectively, to reduce the computer memory. Then, based on deconvolution, the TDCM's of linear components are synthesized from the terminal voltages and currents of step voltage excitation, which are simulated by the finite-difference time-domain (FDTD) method. Finally, transient analysis of a one-dimensional (1-D) discrete-time system is applied to obtain the terminal responses of the microwave active circuits, in which a larger sampled step is chosen to reduce the simulation time. This method is employed to two realistic circuits to validate its efficiency and accuracy. The results are in good agreement with the time-consuming direct FDTD simulation of entire circuits.

Internal and external characteristics in transient forward bias simulations of a-Si:H devices

A numerical program for transient modeling of multilayer a-Si:H devices is described. Using a computer simulation, transient currents in a-Si:H PIN and NIN devices using different magnitudes of step voltage excitations were studied. The results of calculations show first a rapid drop in electric current, followed by an intermediate interval of current rise in both devices. During longer times after step excitation, the transient current in a NIN device decays monotonically towards the new steady-state value, while the current in a PIN device shows a sudden rise to its final value. Such behaviour is explained on the basis of calculated results for different internal quantities such as free and trapped carrier concentrations, space charge density, electric field, potential, net recombination rates and others. It is shown that initially the current in both devices is space-charge limited. The presence of both types of carrier in a PIN diode enables space-charge neutralization at the end of the transient, causing the final abrupt current increase and transition to recombination-limited current flow. The influence of varying the density of localized states (DOS) on simulated transient currents is analyzed and discussed.

Dependence of electrorheological response on conductivity and polarization time.

The mechanisms which govern the performance of electrorheological (ER) fluids must be established if the response times and electrostress levels required for industrial applications are to be achieved. Earlier work by this group has led to a comprehensive description of the electrical and pressure response observed in engineering scale ER valve systems operating under realistic conditions. The present paper carries this program further by showing that in this regime the measured ER valve characteristics are consistent with the polarization-conductance mechanism commonly taken to be the basis for the generation of electrostress. Theoretical descriptions of ER fluids often ignore the role of conductance and frequency dependence of the permittivity. Here, within the context of a model incorporating these material properties and a polarization time, we examine factors affecting the speed, form, and magnitude of ER response. Using this model we are able to establish a relationship between the experimentally observed pressure and current for biased sine and step voltage excitation.

Time domain response of Al/Dy2O3/Al thin film capacitors and their a.c. characteristics

Abstract The charging and discharging current responses of dysprosium oxide thin film sandwiches after step voltage excitation are reported. Experimental measurements were carried out for times ranging from 100 μs to 1000 s and at temperature varying between 298 and 476 K.The transient currents follow the laws I ( t )∝ t − n ( T ) ( n = 0.22 − 0.60) and I ( t ) ∝ t −1.02 for short and long periods respectively. On the basis of the above results a.c. characteristics of the complex capacitance were evaluated and the dielectric response is discussed.

ISOTHERMAL RELAXATION CURRENTS IN ARSENIC CHALCOGENIDES

The transient response to step voltage excitation was investigated for bulk As2S3 and As2Se3 material and in evaporated As2Se3 films. Au and Al were used as electrodes. While in general the response proved to be relaxational, for all As2S3 samples and for the Au/As2Se3/Al substrate cell some additional structure was observed which points to the transit of a finite amount of charge through the sample.

On the transient space-charge-limited current problem

Using a unipolar ion mobility conduction model in planar geometry as suggested by Many and Rakavy, the transient behavior of the bulk electric field and space-charge distribution as a function of space and time is studied. Analytical solutions using the method of self-similar solution of partial differential equations are obtained for both a step voltage and step current excitation.

Charge injection between concentric cylindrical electrodes

The transient electric field and space-charge distributions and terminal voltage-current characteristics are solved for drift-dominated unipolar ion conduction between concentric cylindrical electrodes. Special attention is directed to comparing solutions with charge injection from the inner and outer electrodes. As in past work with parallel-plate geometries, the method of characteristics is used to convert the governing partial differential equations into a set of first-order ordinary differential equations which are easily numerically integrated by the Runge-Kutta method. For current-source excitations the equations can be integrated exactly. Special cases examined include the charging transients to a step voltage or current excitation from rest under space-charge-limited conditions and the discharging transients for systems in the dc steady state which are instantaneously open or short circuited.

Drift-dominated conduction within an Ohmic medium

Drift-dominated charge transport within an Ohmic medium is analyzed using the method of characteristics to convert the governing partial differential equations into a set of ordinary differential equations. As for earlier work within a lossless medium, the analysis is generalized to allow any initial and boundary conditions and any terminal constraint or excitation. For imposed currents the equations are exactly integrable, while for imposed voltages, the equations are easily integrated using the Runge-Kutta method of numerical integration. Special cases examined are the charging transients for space-charge-limited conduction for step current and step voltage excitations from rest and the discharging transients for systems in the dc steady state for which the excitation is instantaneously open or short circuited.