Alternating-current Measurements Research Articles

Use of cloud information technology for control, monitoring, and management of distribution power grids

The use of cloud information technologies for measurement, control, and management of distribution power grids with direct and alternating current couplings are considered. Requirements for databases for carrying out synchronous scalar direct-current measurements and synchronous vector alternating-current measurements are developed. Different scenarios of steady-state and transient regimes are examined. A generalized algorithm for the control and management of the distribution grid is proposed.

Series of 2D Heterometallic Coordination Polymers Based on Ruthenium(III) Oxalate Building Units: Synthesis, Structure, and Catalytic and Magnetic Properties

A series of 2D ruthenium-based coordination polymers with hcb-hexagonal topology, {[K(18-crown-6)]3[M(II)3(H2O)4{Ru(ox)3}3]}n (M(II) = Mn (1), Fe (2), Co (3), Cu (4), Zn (5)), has been synthesized through self-assembly reaction. All compounds are isostructural frameworks that crystallize in the monoclinic space group C2/c. The crystal packing consists of a 2D honeycomb-like anionic mixed-metal framework intercalated by [K(18-crown-6)](+) cationic template. Dehydration processes take place in the range 40-200 °C exhibiting two phase transitions. However, the spontaneous rehydration occurs at room temperature. Both hydrated and dehydrated compounds were tested as Lewis acids heterogeneous catalysts in the acetalyzation of benzaldehyde achieving high yields with the possibility to be recovered and reused. All the investigated materials do not show any long-range magnetic ordering down to 2 K. However, the Fe-based compound 2 presents a magnetic irreversibility in the ZFC-FC magnetization data below 5 K, which suggest a spin-glass-like behavior, characterized also by short-range ferromagnetic correlations. The coercive field increases as the temperature is lowered below 5 K, reaching a value of 1 kOe at 2 K. Alternating current measurements obtained at different frequencies confirm the freezing process that shows weak frequency dependence, being characteristic of a system exhibiting competing magnetic interactions.

AC properties of Pr0.7Ca0.3MnO3 ceramics

Ceramic Pr1-xCaxMnO3(x=0.3) samples are prepared by solid-state reaction and measured using direct current (DC) and alternating current (AC) methods in different magnetic and electrical fields. A Curie temperature of 150 K is determined by I-V measurements in field for Pr0.7Ca0.3MnO3, which is consistent with that from vibrating sample magnetometer (VSM). The AC measurement shows that the grain boundary resistance reduces with magnetic field increasing, while the grain almost keeps unchanged, and it indicates that the colossal magnetoresistance (CMR) effect in low field mainly comes from the grain boundary for the Pr0.7Ca0.3MnO3 ceramic. The barrier height of grain boundary is 117 meV for the Pr0.7Ca0.3MnO3 ceramic, obtained by fitting the temperature spectrum of impedance, and it is well coincident with that from fitting the R-T data. A trap state model is proposed to explain all the measured data.

Electrical properties of dehydrated polyvinyl alcohol

Electrical properties of polyacetylene produced by polyvinyl alcohol dehydration were studied at direct and alternative current measurements. These properties exhibit some a peculiarity at 325 K. It is attributed to two phase coexistence. One of them has a hopping conduction and another one goes from a high-conducting to low-conducting band-type state at 325 K.

A Molecular Half-Wave Rectifier

This paper describes the performance of junctions based on self-assembled monolayers (SAMs) as the functional element of a half-wave rectifier (a simple circuit that converts, or rectifies, an alternating current (AC) signal to a direct current (DC) signal). Junctions with SAMs of 11-(ferrocenyl)-1-undecanethiol or 11-(biferrocenyl)-1-undecanethiol on ultraflat, template-stripped Ag (Ag(TS)) bottom electrodes, and contacted by top electrodes of eutectic indium-gallium (EGaIn), rectified AC signals, while similar junctions based on SAMs of 1-undecanethiol-SAMs lacking the ferrocenyl terminal group-did not. SAMs in these AC circuits (operating at 50 Hz) remain stable over a larger window of applied bias than in DC circuits. AC measurements, therefore, can investigate charge transport in SAM-based junctions at magnitudes of bias inaccessible to DC measurements. For junctions with SAMs of alkanethiols, combining the results from AC and DC measurements identifies two regimes of bias with different mechanisms of charge transport: (i) low bias (|V| < 1.3 V), at which direct tunneling dominates, and (ii) high bias (|V| > 1.3 V), at which Fowler-Nordheim (FN) tunneling dominates. For junctions with SAMs terminated by Fc moieties, the transition to FN tunneling occurs at |V| ≈ 2.0 V. Furthermore, at sufficient forward bias (V > 0.5 V), hopping makes a significant contribution to charge transport and occurs in series with direct tunneling (V ≲ 2.0 V) until FN tunneling activates (V ≳ 2.0 V). Thus, for Fc-terminated SAMs at forward bias, three regimes are apparent: (i) direct tunneling (V = 0-0.5 V), (ii) hopping plus direct tunneling (V ≈ 0.5-2.0 V), and (iii) FN tunneling (V ≳ 2.0 V). Since hopping does not occur at reverse bias, only two regimes are present over the measured range of reverse bias. This difference in the mechanisms of charge transport at forward and reverse bias for junctions with Fc moieties resulted in large rectification ratios (R > 100) and enabled half-wave rectification.

A Comparative Study of the Electrochemical Characteristics of [Emim+][BF4−] and [Bmim+][BF4−] Ionic Liquids at the Surfaces of Carbon Nanotube and Glassy Carbon Electrodes

The electrochemical interfaces of a glassy carbon (GC) electrode and a carbon nanotube (CNT) paper electrode have been studied in 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) and 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) ionic liquids (ILs) using direct current (DC) cyclic voltammetry (CV) and alternating current (AC) electrochemical impedance spectroscopy (EIS). These four electrode/electrolyte combinations serve as representative models of the relatively unconventional, spatially inhomogeneous IL−carbon interfaces that are potentially useful for electrochemical energy-storage/conversion devices. The present work explores in detail the double-layer capacitances as well as other essential electrochemical features of these interfaces. The voltage-dependent double-layer capacitances, and the interfacial charge transfer resistances have been determined within the nonfaradaic windows of these systems, independently, by using CV and EIS. The results of the DC and AC measurements have b...

A Novel Low-Bias Charge Concept for HBT/BJT Models Including Heterobandgap and Temperature Effects—Part I: Theory

A new compact model approach is suggested for the low-bias base charge of homo- and heterojunction bipolar transistors. It is shown that the junction-related (Early) components of this charge depend on an effective doping density. This concept leads to an accurate description with the conventional capacitance-charge model formulas but using different parameters directly extracted from direct-current measurements instead of the classical parameter values derived from alternating-current measurements. The temperature dependence of the low-bias base charge has also been revised, resulting in a new term added to the currently adopted temperature law. The applied novel analytic technique made it possible to determine the influence of bandgap narrowing (BGN) effects and Ge doping on the temperature behavior of SiGe transistors.

Alternating current investigation and modeling of the temperature and ozone effects on the grains and the grain boundary contributions to the WO 3 sensor responses

We report a parametric investigation of the electrical property evolution of WO 3 thin films in ozone. The effect of working temperature and ozone concentration on sensors' sensitivity has been studied by alternating current (AC) impedance spectroscopy. An electrical model of resistance and capacitor circuit was used to fit the experimental spectra. It was demonstrated that the best sensors' sensitivity is obtained in the working temperature range of 250 to 300 °C. A tentative interpretation of the sensors' response evolution has been made by modeling of the ozone concentration effect on the WO 3 sensitive layer impedances after obtaining additional AC measurements. The contributions of the grains and grain boundaries to the overall response of the WO 3 based sensors were dissociated.

Noise Reduction of Carbon Nanotube Field-Effect Transistor Biosensors by Alternating Current Measurement

We demonstrated a marked improvement of sensitivity (signal-to-noise ratio) in carbon nanotube field-effect transistor (CNTFET) sensors. The alternating current (AC) measurement with a lock-in amplifier, which suppresses the fluctuations in drain current in CNTFETs without decreasing the signal level, was adopted. The noise level of CNTFETs used in buffer solutions was greatly decreased by AC measurement. Furthermore, we investigated the sensing operations of CNTFET pH sensors and biosensors by AC measurement. The sensing performance of CNTFET sensors was markedly improved. The signal-to-noise ratio of pH sensors measured using AC was six times higher than that obtained by direct current (DC) measurement. A small amount of bovine serum albumin of 250 pM was effectively detected by CNTFET biosensors by AC measurement.

A study on ac and dc conductivity characteristics of Y-doped BaCeO 3 modified by Ar + ion beam

The effects of surface modification on electrical characteristics in bulk, grain boundary and interface (electrolyte/electrode) of BaCe 0.9Y 0.1O 3-δ were investigated. The surface modification was performed by means of two processes: specimen was firstly irradiated by 10 keV Ar + ion with dose of 1 × 10 18 ions/cm 2 and then exposed to air. The modified surface was investigated by elastic recoil detection analysis (ERDA) for quantitative analysis of hydrogen concentration on the surface and alternating current (AC) and direct current (DC) conductivity measurements, respectively. The ERDA results showed that hydrogen concentration and reaction rate on the modified surface increased. The increase of hydrogen concentration was explained in terms of the increase of proton due to interaction between oxygen vacancy formed by modification and H 2O. In AC and DC electrical conductivity measurements, it concluded that the proton and electronic carrier generated on the surface by modification attributed to the increase of bulk, grain boundary and interface conductivity.

Frequency Response of SWCNT Field-Effect Transistors with MWCNT Interconnects

Single-walled carbon nanotube field-effect transistors (SWCNT FETs) with multi-walled carbon nanotubes (MWCNTs) as interconnects were fabricated, and their field effect properties were measured and compared with those of the case with metal leads as interconnects. Both cases showed almost the same direct current (DC) response, while the MWCNTs interconnected case showed a little better alternating current (AC) properties. AC measurement showed that the MWCNTs interconnected SWCNT FETs worked well at frequency up to 20 MHz.

A method for determining electrophoretic and electroosmotic mobilities using AC and DC electric field particle displacements

We have developed a method for measuring the electrophoretic mobility of submicrometer, fluorescently labeled particles and the electroosmotic mobility of a microchannel. We derive explicit expressions for the unknown electrophoretic and the electroosmotic mobilities as a function of particle displacements resulting from alternating current (AC) and direct current (DC) applied electric fields. Images of particle displacements are captured using an epifluorescent microscope and a CCD camera. A custom image-processing code was developed to determine image streak lengths associated with AC measurements, and a custom particle tracking velocimetry (PTV) code was devised to determine DC particle displacements. Statistical analysis was applied to relate mobility estimates to measured particle displacement distributions.

Couches minces diélectriques de phosphate d'aluminium

Aluminium phosphate thin films on silicium substrate have been carried out from tributylphosphate and aluminium acetylacetonate precursors in solution through the pyrosol process. It can be observed a large range of chemical analysis in terms of experimental conditions. These thin films have been characterized by X-ray diffraction and infrared spectrometry. Their electrical characteristics, defined from direct current and alternative current measurements, are quite different to those of the crystallized phosphate and can be explained by P-O and Al-O dangling bond existence

Alternating-current measurement and noninvasive data ring utilizing the Faraday effect in a closed-loop fiber magnetometer

A novel fiber-optic polarimetric configuration for a magnetometer utilizing the Faraday effect is described. The system is operated in a closed-loop mode using magneto-optic feedback through a simple current-driven solenoid to maintain the azimuth of the optical output from the polarimeter constant. In this mode of operation scale-factor errors due to changes in the Verdet constant of the fiber are effectively eliminated. The minimum detectable current was less than 1 mA, with linear operation up to several amperes. A multiplexed system was also demonstrated, with potential application as a multiaccess noninvasive data ring.

Some Measurements on the Validity of the Principle of Superposition in Solid Dielectrics

Alternating-current measurements in carnauba wax in the frequency range between 20 c/sec. and 20 Mc/sec. are reported and the correlation of the experimental data in terms of the principle of superposition is given.

Balance methods in alternating-current measurement

C. L. Fortescue: This question of Null measurement is one that has been discussed in the Institute in the past quite a good deal. I think that Null methods of calibrating current transformers are in general use now. We ourselves have used a method of calibrating current transformers which was described by me in the Institute JOURNAL some time ago, in which variable mutual inductances were used. At that time we used d'Arsonval portable type galvanometer, and a synchronous contactor. This method was quite satisfactory so long as the contactor was properly maintained; but as we were using this apparatus right on our test floor, with green operators from time to time, who had to be trained to use the device, it was difficult to get them familiar enough with it to be able to tell when it was working properly, and the results were sometimes erratic.

A dynamometrical comparator: A differential dynamometer for accurate comparison of alternating and direct-current strengths

IN a direct-current measuring instrument, the deflection is usually proportional to the strength of the current to be measured, and it is also proportional to the strength of a magnetic field, produced by permanent magnets. In the corresponding alternating-current instrument, the magnetic field must ordinarily be produced by the measured current itself, and the deflection will therefore be inherently quadratic with respect to the measured quantity. In a thermal instrument, the heating effect of the current is observed, and the scale is likewise quadratic. This correspondingly holds for electrostatic alternating-current instruments. With this inevitable second-power relation follows uneven scale divisions, and poor sensitivity at low values, two circumstances which have a decidedly detrimental effect upon the accuracy of alternating-current measurements. In work requiring a high degree of precision, some indirect method is therefore often employed, and the alternating-current measurement is reduced to a direct-current measurement by use of an intermediate apparatus, which may be generally called a comparator. By aid of the comparator some effect of the alternating current to be measured is either observed, through direct-current measurements, or neutralized by means of a direct current, the exact value of which may be determined with the extremely high accuracy of the direct-current potentiometer.

Bridge Methods for Alternating-Current Measurements

Bridge Methods for Alternating-Current Measurements

Bridge methods for alternating-current measurements

THE extension of the field of application of electric energy to human service requires more and more of measurements of electrical quantities, of varying grades of precision. Very prominent in the history of electrical measurements is the so-called “bridge” method, the fundamental principle of which is the equalizing of the potentials of two chosen points in a network of electric circuits. The original application of this principle was made by S. H. Christie in 1833 to the measurement of resistance to direct current in the arrangement long familiarly known as the Wheatstone Bridge. Numerous forms of Wheatstone Bridge for direct-current measurement have been developed. The conditions for its use have been investigated thoroughly and are well-known.

A study of electromagnet moving-coil galvanometers for use in alternating-current measurements

A study of electromagnet moving-coil galvanometers for use in alternating-current measurements