Excitation Voltage Research Articles

Enhancement of the carboxymethylation of corn starch via induced electric field

This study aimed to enhance the synthesis of carboxymethyl starch (CMS) by induced electric field (IEF). Corn starch was alkalized, pumped into IEF system, and then reacted with monochloroacetic acid at excitation voltages of 0–400 V. IEF enhanced the carboxymethylation by accelerating the rate of OH− and ClCH2COO− attacking starch particles and slightly intensifying the thermal effect by ~7.1 °C (30 min). Compared with the control (0 V), IEF increased the degree of substitution and reaction efficiency by 0.056–0.148 and 9.37–24.56 %, caused more destruction in starch granular and crystal structure, and thus increased its water solubility, swelling power, and paste transparency. Furthermore, some new crystals were formed during IEF treatment, which enhanced the thermostability of CMS, showing an increase of the maximum decomposition temperature by 16–26 °C. Overall, the results classified that IEF could improve the carboxymethylation and enhance the thermostability of products, which provided guides for the applications of electro-techniques in starch modification involving charged species.

Design and dynamic analysis of a novel compound bending hollow piezoelectric beam miniature rotary actuator

In this paper, a miniature hollow piezoelectric beam rotary actuator is proposed and designed based on the compound bending vibration modes. The structure body is designed as an elastic hollow square beam with symmetrical piezoelectric patches attached at both ends, which directly eliminates the step of the frequency tuning. A conical rotor is driven by the hollow piezoelectric beam through the elliptical motions of the points on its inner surface. Based on the Timoshenko beam theory and Lagrange equation, the numerical continuum model is established to analyze the working mechanism. A prototype of the miniature rotary actuator with a size of 50 × 6 × 6 mm (2 mm through-hole) is manufactured and its performance under various excitation parameters is characterized in rotor speed experiments. The experimental results show that the maximum speed of the conical rotor is 913 rpm at the excitation voltage of 400 V. With a maximum load of 70.31 mN, the spherical rotor can achieve a speed of 450 rpm. The numerical results are in great agreement with the experimental results, so the output characteristics of the rotary actuator can be estimated. The simulation and test results demonstrate that the proposed rotary actuator has outstanding output performance and controllability. In addition, the simple structure design is easy to realize the frequency tuning and miniaturization.

Characterization of DC corona discharge current pulses using high-frequency measurement techniques

This paper presents corona discharge current pulse characterization under positive and negative DC voltage excitations. Two electrode systems with three different gap spacings generated corona discharges. Different corona modes in atmospheric air were observed with voltage level changes. Commercial shunt resistors and a high-frequency current transformer (HFCT) captured corona current pulses. The appropriate resistor type and value were determined for the shunt resistor measurement. BNC terminator was proposed as a shunt resistor to detect corona discharge current pulses, and the availability of the shunt resistors and HFCTs for corona pulse detection was discussed. After gathering corona discharge pulse data, features from the pulses were extracted. The best features describing corona discharge types were specified using a recursive feature elimination method based on a decision tree estimator. The corona discharges were discriminated with an accuracy rate of 0.994.

The magnetic field design of a solenoid for the cold-cathode Penning ion source of a miniature neutron tube

A high-yield and beam-stable neutron tube can be applied in many fields. It is of great significance to the optimal external magnetic field intensity of the cold-cathode Penning ion source (PIS) and precisely controls the movement of deuterium (D), tritium (T) ions and electrons in the source of the neutron tubes. A cold-cathode PIS is designed based on the solenoidal magnetic field to obtain better uniformity of the magnetic field and higher yield of the neutron tube. The degree of magnetic field uniformity among the magnetic block, double magnetic rings and solenoidal ion sources is compared using finite element simulation methods. Using drift diffusion approximation and a magnetic field coupling method, the plasma distribution of hydrogen and the relationship between plasma density and magnetic field intensity at 0.06 Pa pressure and a solenoid magnetic field are obtained. The results show that the solenoidal ion source has the most uniform magnetic field distribution. The optimum magnetic field strength of about 0.1 T is obtained in the ion source at an excitation voltage of 1 V. The maximum average number density of monatomic hydrogen ions (H+) is 1 × 108 m−3, and an ion-beam current of about 14.51 μA is formed under the −5000 V extraction field. The study of the solenoidal magnetic field contributes to the understanding of the particle dynamics within the PIS and provides a reference for the further improvement of the source performance of the neutron tube in the future.

Characterisation of an independently controlled coaxial synthetic jet

This paper presents the hot-wire measurements to characterise the flow field of a novel coaxial synthetic jet (CSJ) actuator. The CSJ actuator is formed by positioning two single-acting synthetic jet (SJ) actuators coaxially (0° orientation angle) along with their own flow actuation mechanism (piezo-electric diaphragms). The CSJ is formed by the periodic suction and expulsion of the fluid into a quiescent medium employing the piezo diaphragms through the inner and annular openings (orifices), which have an equal hydraulic diameter (dh) of 3 mm. This novel configuration facilitates independent control of excitation voltage (V), frequency (f) for inner and annular jets, and additionally, various phase differences (∅s) between the inner and annular jets. The resonance frequency of both the inner and annular cavities are obtained separately as 350 Hz, and 320 Hz, respectively. The inner jet is operated at Reynolds number Re=1100 (V=50 V, and f=350 Hz), which remains fixed for all the test cases. The CSJ flow field is analysed for three mass flux ratios (Mrs) as 0.7, 1.0, and 2.0, which are achieved by operating both the diaphragms independently at various excitation voltages for a fixed f=350 Hz, and at various fs for a fixed excitation voltage of 50 V. Moreover, the effect of ∅s (range: 0° to 180° in the step of 45°) by leading the inner or annular jet is examined while the CSJ is operated at these Mrs. It has been observed that the strength and spreading of the CSJ can be enhanced by providing ∅s between the jets, without investing any additional power for flow excitation. It is important to notice that leading the weaker jet enhances its contribution to the creation of the CSJ, which improves the CSJ's strength and spread. The CSJ flow field is compared with that of the inner SJ, and annular SJ, operated individually, to illustrate the superior performance of the CSJ. The paper conveys that the CSJ’s strength and spreading can be manipulated significantly with the independent control facility, which is feasible with this configuration.

A method to evaluate the inductance properties of REBCO excitation process based on magnetic energy density and T–A formula

The REBCO high-temperature superconducting tape has a pronounced electromagnetic anisotropy. The critical current is strongly dependent on the value of the magnetic field, the magnetic field direction, the temperature, and the stress, and has a significant nonlinear relationship. It is also important to note that screening current effects in superconducting magnets at elevated temperatures lead to a non-uniform distribution of current densities, and thus the inductance of superconducting magnets at high-temperatures is calculated differently from that of normal magnets. This is essential for the design of superconducting energy storage magnets at high-temperatures, especially for the accurate evaluation of the inductance values. To further analyze the variation of the inductance value due to the REBCO screening current, the T–A formulation combined with the magnetic energy density is considered to evaluate the energy storage and inductance values during the excitation of the superconducting coil. The effect of excitation rate, operating temperature, and excitation current on the inductance value is analyzed based on the design of a 5 T insulating superconducting coil. The mathematical relation between excitation voltage, contact resistance, and inductance in the magnetic excitation experiment is presented, and the accuracy of the calculated method is verified by comparison with simulation results.

A resonant single-wing bionic piezoelectric motor based on a biasing self-clamping mechanism.

In this study, a resonant single-wing bionic piezoelectric motor based on a biasing self-clamping mechanism inspired by dragonfly flight was designed, assembled, and tested. The main mechanism of the designed piezoelectric motor includes a mover (including a vibrator, clamping foot, bionic pedestal, etc.), a stator, and other auxiliary components. The clamping foot of the mover contacts the side of the stator to form a biasing self-clamping mechanism, which can achieve a clamping effect within half a cycle of the vibrator's resonant vibration. The piezoelectric plate on the vibrator receives a single harmonic excitation from the signal generator, causing the base plate to bend and distort. The base plate drives the clamping foot to move regularly, causing the mover to perform a linear motion. Moreover, repeated single harmonic excitations can realize the continuous movement of the mover. The structure of the piezoelectric motor was optimized using COMSOL6.0, which is a finite element analysis software. The first-order bending vibration of the vibrator was chosen as the working mode through finite element simulation, and an experimental platform was built. The performance of the prototype piezoelectric motor was tested and verified on the experimental platform. The final experimental data show that under the conditions of 300Vp-p excitation voltage and 109Hz driving frequency, the maximum no-load speed of the prototype reaches 6.184 mm/s, and the maximum load of the motor is 4g.

Substitution Method for the Analysis of Systems Based on Two Nonlinear Resonators

Circuits containing two nonlinear resonators have recently been proposed for nonreciprocal isolators, robust wireless power transfer, and sensors. A fundamental characteristic is the presence of hysteresis, associated with points of infinite slope in the solution curves. However, the prediction of hysteresis in the presence of the two distinct resonators is not possible in default harmonic balance (HB) and the additional use of continuation techniques may not be exhaustive enough. Here, we present a novel substitution method, based on the use of two auxiliary generators (AGs), that enables the system control through a single excitation voltage. A simple condition is also provided to obtain all the existing loci of infinite-slope points. The methods, which are compatible with commercial HB, will be illustrated through their application to a Lorentzian–Fano nonlinear isolator.

Development of a resonant screw-driven piezoelectric motor operating in single-mode vibration.

A resonant screw-driven piezoelectric motor operating in single-mode vibrations is proposed, designed, manufactured, and studied. The motor is constructed with a stator and a threaded rotor. The stator consists of a hollow parallelogram metal elastomer and two piezoelectric ceramic plates. The motor is excited by a single-phase signal to produce two separate vibration modes: the first expansion mode (B1 mode) and the second expansion mode (B2 mode). Each mode drives the threaded rotor in one direction, and the bidirectional motion is achieved by switching the two modes. The construction is designed, and modal simulation is performed using finite element software to determine the structural parameters. A frequency-domain analysis is performed to obtain the frequency response characteristics, and the motion trajectories of the stator are obtained using transient analysis. Finally, a prototype is produced, and experiments are conducted. Experimental results indicate that the no-load speeds of the motor under the 200 Vp-p voltage excitation are 1.67 and 1.04 mm/s in the two modes, which correspond to maximum loads of 35 and 20mN, respectively.

A thin-film acoustic metamaterial absorber with tunable sound absorption characteristics.

A thin-film absorber with tunable acoustic properties over a wideband is designed based on the acoustic metamaterial theory. The thin-film acoustic metamaterial absorber (TFAMA) consists of a frame made of piezoelectric material and several flexible films with attached mass blocks (mass-spring vibration system). Based on the vibration mechanism of the mass-spring vibration system, a cellular model of local resonance form is established, and the material properties of negative effective mass are discussed. Combined with the vibration modal analysis of the coupling of mass block, elastic film, and piezoelectric material, the acoustic characteristics of the TFAMA under alternating voltage excitation are studied by finite element and experimental methods. The simulation and experimental results show that the sound wave can be well absorbed when it is incident on TFAMA to cause the membrane-cavity coupling resonance. By applying an alternating voltage to the TFAMA to excite the mass-spring vibration system to generate local resonance, the absorption of sound waves can be further enhanced in a relatively wide band near the excitation frequency. In view of the convenience of voltage parameter adjustment, the sound absorption band can be flexibly tuned in a wide range, including low frequency.

A Dual-Frequency-Detuning Method for Improving the Coupling Tolerance of Wireless Power Transfer

This letter proposes a dual-frequency-detuning method for wireless power transfer systems to gain a smooth power profile in large coupling variation ranges. The application of the detuning method in the dual-frequency resonant network is explored to adjust the equivalent impedance of each frequency channel at different coupling conditions. Accordingly, the proposed method can freely regulate the voltage gain and output power curves even under a square-wave voltage excitation with high-order harmonic components. By designing the system properly, both the fundamental and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> frequency channels alternately serve as the main power transfer channel under strong and weak coupling conditions, so less power fluctuation over a large coupling variation is realized. A 130W prototype is developed, and the experimental results show that the maximum power fluctuation is less than 6.8% against coupling coefficient variations from 0.35 to 0.74.

Research on the Directional Adaptability of a Self-Adaptive Energy Harvester.

With the continuous development of wireless sensor networks (WSNs), multi-directional energy harvesting technology has received widespread attention from scholars. In order to evaluate the performance of multi-directional energy harvesters, this paper uses a directional self-adaptive piezoelectric energy harvester (DSPEH) as an example, defines the direction of the excitation in three-dimensional space, and studies the influence of excitations on the key parameters of the DSPEH. The rolling angle and pitch angle are used to define complex excitations in three-dimensional space, and the dynamic response of the excitation changes in a single direction and multiple directions is discussed. It is noteworthy that this work presents the concept of "Energy Harvesting Workspace" to describe the working ability of a multi-directional energy harvesting system. The workspace is expressed by the excitation angle and voltage amplitude, and energy harvesting performance is evaluated by the volume-wrapping method and area-covering method. The DSPEH exhibits good directional adaptability in two-dimensional space (rolling direction); in particular, when the mass eccentricity coefficient is r = 0 mm, 100% of the workspace in two-dimensional space is obtained. The total workspace in three-dimensional space depends entirely on the energy output in the pitch direction.

Identification of Electrical Tree Aging State in Epoxy Resin Using Partial Discharge Waveforms Compared to Traditional Analysis.

Electrical treeing is one of the main degradation mechanisms in high-voltage polymeric insulation. Epoxy resin is used as insulating material in power equipment such as rotating machines, power transformers, gas-insulated switchgears, and insulators, among others. Electrical trees grow under the effect of partial discharges (PDs) that progressively degrade the polymer until the tree crosses the bulk insulation, then causing the failure of power equipment and the outage of the energy supply. This work studies electrical trees in epoxy resin through different PD analysis techniques, evaluating and comparing their ability to identify tree bulk-insulation crossing, the precursor of failure. Two PD measurement systems were used simultaneously-one to capture the sequence of PD pulses and another to acquire PD pulse waveforms-and four PD analysis techniques were deployed. Phase-resolved PD (PRPD) and pulse sequence analysis (PSA) identified tree crossing; however, they were more sensible to the AC excitation voltage amplitude and frequency. Nonlinear time series analysis (NLTSA) characteristics were evaluated through the correlation dimension, showing a reduction from pre- to post-crossing, and thus representing a change to a less complex dynamical system. The PD pulse waveform parameters had the best performance; they could identify tree crossing in epoxy resin material independently of the applied AC voltage amplitude and frequency, making them more robust for a broader range of situations, and thus, they can be exploited as a diagnostic tool for the asset management of high-voltage polymeric insulation.

A public data-set for synchronous motor electrical faults diagnosis with CNN and LSTM reference classifiers

In the last two decades, motor operation monitoring tools have become a necessity, and many studies focus on the detection and diagnosis of motor electrical faults. However, at present, a core obstacle that prevents the direct comparison of such classification techniques is the lack of a standard database that can be used as a benchmark. In view of this, we offer here a public experimental data-set that has beendesigned specifically for the comparison of synchronous motor electrical fault classifiers. The data-set comprises five types of motor electrical faults: open phase between inverter and motor; short circuit/leakage current between two phases; short circuit/leakage current in phase-to-neutral; rotor excitation voltage disconnection; and variation of rotor excitation current. In addition, each fault has been recorded as a four-dimensional signal: three phase voltages; three phase currents; motor speed; and motor current. The package includes two deep-learning reference classifiers that are based on a convolutional neural network (CNN) and long short term memory (LSTM). Due to the good performance of these classifiers, we suggest that they can be used by the community as benchmarks for the development of new and better motor electrical fault classification algorithms. The database and the reference classifiers are examined and insights regarding different combinations of features and lengths of recording points are provided. The developed code is available online, and is free to use.

IMPROVEMENT OF THE ENERGY PERFORMANCE OF ASYMMETRIC EXCITORS OF SYNCHRONOUS MACHINES IN VOLTAGE FORCING MODES

The main mode of operation of synchronous machines in electric drives of industrial plants is the mode in which a static load moment close to the nominal is applied to the shaft. If the synchronous machine works as a generator, when consumers of comparable power are connected to the stator to stabilize the output voltage of the generator, forcing of the excitation voltage is applied by influencing the control angles of the thyristors of the controlled rectifier. In the nominal mode, the control angles of the thyristors of the exciter are significant, which makes it possible to ensure a sufficient multiplicity of the voltage during forcing. But with significant thyristor opening angles, the controlled rectifier consumes significant reactive power, which reduces the power factor of the rectifier bridge. In addition, forcing the excitation voltage is necessary for synchronous motors when a significant load is applied to the shaft and when voltage drops in the power supply network.&#x0D; It is widely used to connect capacitors in parallel to the windings of the power transformer, or to use two zero diodes that are connected in series and connected to the output of the exciter to improve its energy performance. A significant improvement in the power factor can be achieved by using forced capacitive switching nodes. However, the improvement of energy indicators by turning on zero diodes and capacitors leads to a significant change in the harmonic composition of the excitation voltage. In the work, a research of the harmonic composition of the excitation voltage of synchronous machines with asymmetric bridge rectifiers using artificial commutation circuits was carried out. &#x0D; To research the harmonic composition, experimentally obtained dependences of the forced excitation voltage, which are decomposed into a trigonometric series, are used. Calculated amplitude spectra of the excitation voltage during natural and forced switching of thyristors. The above calculations show that the coefficient of ripples of the output voltage of the thyristor exciter when using a rectifier with forced commutation is more than two times less (5.4 %) than the coefficient of ripples of the output voltage of a rectifier with natural commutation (11.2 %). The conducted experiments and the results of their analysis proved the expediency of using the developed exciter with forced capacitive commutation.

Experimental Study on Downhole Acoustic Wave Propagation Characteristics in Curved Drill String

Aiming at the problem of the unclear sound wave attenuation in the signal transmission of the load-bearing drill string, an experimental device for the sound wave propagation characteristics in the curved drill string was set up. The influence of the drill string structure and acoustic excitation parameters on the sound propagation characteristics in the drill string under different loads is different. The results show that the curvature of the drill string has an influence on the propagation of the sound wave in the drill string, and its rule is related to the curvature of the drill string and the frequency of the sound wave. The pulse repetition rate, excitation voltage, and pulse width only affect the passband amplitude, and the effect is significantly greater than the curvature of the drill string. The main influencing factor of its sound transmission characteristics is the degree of drill string curvature. The low-frequency signal should be preferentially selected as the carrier of downhole information transmission after considering the influence of drill string bending on acoustic transmission.

Imaging of Fiber Waviness in Thick Composites with Unknown Material Properties Using Probability-Based Ultrasound Non-Reciprocity.

Fiber waviness and voids may be produced in thick composites due to improper manufacturing conditions and consequently pose a risk of structural failure. A proof-of-concept solution for imaging fiber waviness in thick porous composites was proposed from both numerical and experimental studies, via calculating ultrasound non-reciprocity along different wave paths in a sensing network constructed by two phased array probes. Time-frequency analyses were conducted to reveal the cause of ultrasound non-reciprocity in wavy composites. Subsequently, the number of elements in the probes and excitation voltages was determined for fiber waviness imaging using the ultrasound non-reciprocity with a probability-based diagnostic algorithm. The fiber angle gradient was observed to cause ultrasound non-reciprocity and fiber waviness in the thick wavy composites were successfully imaged regardless of presence of voids. This study proposes a new feature for the ultrasonic imaging of fiber waviness and is expected to contribute to processing improvement in thick composites without prior knowledge of material anisotropy.

Nonlinear vibrations of a dielectric elastomer cantilever combined-stepped-plate actuator

A dielectric elastomer (DE) cantilever combined-stepped-plate actuator is proposed and its nonlinear vibration enhancement behaviors are investigated. The irregular geometry of the actuator is transformed into a rectangular computational domain with the ideal of the iso-parametric element transformation; then the governing equations describing the nonlinear vibration of the actuator are formulated by the variational method. The nonlinear periodic responses are solved through the harmonic balance method and the arc-length continuation method. The results indicate that the single side (upper or lower) voltage excitation is more efficient in the actuating performance. The asymmetrical combined plate presents a better motion performance comparing with the symmetrical one. Not only can more drive modes be achieved (For instance, both symmetrical flapping mode and asymmetrical torsional mode can be excited by changing the voltage frequency), but also higher responses can be obtained. Additionally, isolated responses are found for some particular dimension parameters, which provides a potential design strategy to regulate the frequency domain of significant responses. This research concludes that, the asymmetrical combined plate subjected to an asymmetrical voltage loading would show a more efficient locomotion performance, which can provide an insight into the structural design and the excitation strategy for DE actuators.

Numerical Simulation Research on Partial Discharge of Particle Defects at Epoxy Interface Excited by High-Frequency Sinusoidal Voltage.

In order to improve the effectiveness of partial discharge detection in attached metal particle insulators, this paper proposes a partial discharge detection method for particle defects in insulators under high-frequency sinusoidal voltage excitation. In order to study the development process of partial discharge under high-frequency electrical stress, a two-dimensional plasma simulation model of partial discharge with particle defects at the epoxy interface is established under plate-plate electrode structure, which realizes the dynamic simulation of particulate defect partial discharge. By studying the microscopic mechanism of partial discharge, the spatial and temporal distribution characteristics of microscopic parameters such as electron density, electron temperature, and surface charge density are obtained. Based on this simulation model, this paper further studies the partial discharge characteristics of epoxy interface particle defects at different frequencies, and verifies the accuracy of the model from two aspects of discharge intensity and surface damages through experimental means. The results show that with the increase in the frequency of applied voltage, the amplitude of electron temperature shows an increasing trend. However, the surface charge density gradually decreases with the increase in frequency. These two factors make partial discharge severest when the frequency of the applied voltage is 15 kHz.

Nonlinear bifurcations of a circular dielectric-elastomer resonator based on a modified incremental harmonic balance method

When dielectric-elastomer (DE) resonators are operated under large alternating voltage excitations, strong geometric and material nonlinearities can significantly affect the dynamic performance. Based on the virtual work principle, a dynamic model of a circular DE resonator is established in this work. Static analysis is conducted to study the impacts of the control voltage on the strain and natural frequency of the DE resonator at equilibrium. A modified Incremental Harmonic Balance and arc-length methods are used to obtain dynamic responses of the system excited by alternating voltages, and stability analysis is conducted using the Floquet theory. The effects of the mechanical parameters are studied, and period-doubling bifurcations are observed, which are produced by the parametric excitation of the voltage. The bifurcation phenomenon is comprehensively investigated through analysis of the voltage, stress, and damping coefficient, which provides design guidance for DE resonators.