Alternating Current Voltage Research Articles

Resonant oscillation of droplets under an alternating electric field to enhance solute diffusion

This study investigates a novel microfluidic mixing technique that uses the resonant oscillation of coalescent droplets. During the vertical contact-separation process, solutes are initially separated as a result of the combined effects of diffusion and gravity. We show that the application of alternating current (AC) voltage to microelectrodes below the droplets causes a resonant oscillation, which enhances the even distribution of the solute. The difference in concentration between the top and bottom droplets exhibits frequency dependence and indicates the existence of a particular AC frequency that results in a homogeneous concentration. This frequency corresponds to the resonance frequency of the droplet oscillation that is determined using particle tracking velocimetry. To understand the mixing process, a phenomenological model based on the equilibrium between surface tension, viscosity, and electrostatic force was developed. This model accurately predicted the resonance frequency of droplet flow and was consistent with the experimental results. These results suggest that the resonant oscillation of droplets driven by AC voltage significantly enhances the diffusion of solutes, which is an effective approach to microfluid mixing.

DC vs AC Electrokinetics-Driven Nanoplasmonic Raman Monitoring of Charged Analyte Molecules in Ionic Solutions.

Electrokinetic surface-enhanced Raman spectroscopy (EK-SERS) is an emerging high-order analytical technique that combines the plasmonic sensitivity of SERS with the electrode interfacial molecular control of electrokinetics. However, previous EK-SERS works primarily focused on non-Faradaic direct current (DC) operation, limiting the understanding of the underlying mechanisms. Additionally, developing reliable EK-SERS devices with electrically connected plasmonic hotspots remains challenging for achieving high sensitivity and reproducibility in EK-SERS measurements. In this study, we investigated the use of two-tier nanolaminate nano-optoelectrode arrays (NL-NOEAs) for DC and alternating current (AC) EK-SERS measurements of charged analyte molecules in ionic solutions. The NL-NOEAs consist of Au/Ag/Au multilayered plasmonic nanostructures on conductive nanocomposite nanopillar arrays (NC-NPAs). We demonstrate that the NL-NOEAs exhibit high SERS enhancement factors (EFs) of ∼106 and can be used to modulate the concentration and orientation of Rhodamine 6G (R6G) molecules at the electrode surface by applying DC and AC voltages. We also performed numerical simulations to investigate the ion and R6G dynamics near the electrode surface under DC and AC voltage modulation. Our results show that AC EK-SERS can provide additional insights into the dynamics of molecular transport and adsorption processes compared to DC EK-SERS. This study demonstrates the potential of NL-NOEAs for developing high-performance EK-SERS sensors for a wide range of applications.

Enhancing hydrogen generation through advanced power conditioning in renewable energy integration

Producing hydrogen using renewable energy is a pivotal move towards cleaner and eco-friendlier energy generation, playing a vital role in safeguarding the environment. This method merges power electronic tools with electrolysers, which are key in enhancing hydrogen creation efficiency. Given that electrolysis operate on direct current (DC) voltage, there's a need for DC-DC or AC-DC converters to guarantee the right voltage and current for optimal electrolysis. This study aims to present a power regulation system tailored for hydrogen production powered by renewable resources. This system consists of two main stages: the matrix converter and the 12-pulse diode rectifier. The matrix converter ensures a controlled intake of current from the alternating current (AC) side, leading to a sinusoidal output with limited harmonic disruption. Additionally, it produces an AC voltage with a controlled magnitude and frequency, designed to suit the 12-pulse diode rectifier that follows. This meticulous voltage control is fundamental, granting enhanced operational adaptability and producing a high-quality waveform to support the electrolysis. Finally, the 12-pulse diode rectifier's task is to transform the AC from the matrix converter into a consistent DC voltage, crucial for effective hydrogen production.

Study on the partial discharge characteristics induced by the motion of cellulose particles in transformer oil

AbstractCellulose particles present a significant concern within the oil‐paper insulation of transformers, posing potential risks to insulation performance. Under the influence of the electric field, the movement of cellulose particles can compromise the transformer's insulation, leading to potential failure. An experimental platform was established to synchronously record particle motion images, partial discharge (PD) pulses, and electric voltage waveforms in oil, aiming to observe the PD characteristics resulting from particle motion under alternating current (AC) voltage and investigate the relationship between different particle motion modes, motion positions, and PD signals. The findings reveal that the phase distribution of PD signals is correlated with the particle motion mode. Specifically, the phase distribution of PD pulses during the back‐and‐forth motion mode is between 4°–94° and 182°–275°. In the suspended oscillation motion mode, the PD pulses phase is concentrated between 20°–84° and 203°–268°. The generation of PD pulses is closely linked to the particle's motion position. PD pulses occur when the particle remains on the electrode during the back‐and‐forth motion mode, generally, PD pulses rarely occur during the jumping process between the two electrodes. In the suspended oscillation motion mode, PD pulses occur when the particle moves upward, but generally do not occur during downward movement. Furthermore, the Pulse Sequence Analysis technique was used to employ the PD characteristics caused by particle motion in transformer oil. The simulation calculations of the electric field distribution for two different particle motion modes show that the particle's motion can cause distortion of the electric field distribution, leading to the generation of PD. The study of the PD characteristics at different particle motion modes and positions obtained contributes to a deeper understanding of the PD induced by cellulose particle motion under AC voltage and provides a reference for the insulation evaluation of transformers.

One-Shot Remote Integration of Macromolecular Synaptic Elements on a Chip for Ultrathin Flexible Neural Network System.

The field of biomimetic electronics that mimicsynapticfunctionshas expanded significantly to overcome the limitationsofthevon Neumann bottleneck. However, the scaling down of the technology has led to an increasingly intricate manufacturing process. To address the issue, this work presents a one-shot integrable electropolymerization (OSIEP) method with remote controllability for the deposition of synaptic elements on a chip by exploiting bipolar electrochemistry. Condensing synthesis, deposition, and patterning into a single fabrication step is achieved by combining alternating-current voltage superimposed on direct-current voltage-bipolar electropolymerization and a specially designed dual source/drain bipolar electrodes. As a result, uniform 6 × 5 arrays of poly(3,4-ethylenedioxythiophene) channels are successfullyfabricatedon flexible ultrathin parylene substrates in one-shot process. The channels exhibited highly uniform characteristics and are directly used as electrochemical synaptic transistor with synaptic plasticity over 100 s. The synaptic transistors have demonstrated promising performance in an artificial neural network (NN) simulation, achieving a high recognition accuracy of 95.20%. Additionally, the array of synaptic transistor is easily reconfigured to a multi-gate synaptic circuit to implement the principles of operant conditioning. These results provide a compelling fabrication strategy for realizing cost-effective and disposable NN systems with high integration density.

Research on double resonant excitation in a triangular electrode ion trap with asymmetric geometry.

The triangular electrode linear ion trap with asymmetric geometry has been reported to possess a high ion unidirectional ejection efficiency and a reasonable mass resolution. To further improve its performance, a double resonant excitation method involving a dipolar and a quadrupolar resonant excitation was applied here. The dipolar excitation method was carried out by applying a supplementary alternating voltage out of phase to one pair of the electrodes, whereas the quadrupolar excitation (QE) method was carried out by adding a supplementary alternating voltage in phase to another pair of electrodes. Numerical simulations were performed to explore the impact of the frequency difference between the alternating current (AC) and the QE voltage (∆ω), the frequency of the AC voltage (ωAC), and the QE voltage amplitude (VQE). The mass resolution could be improved to ~4700 , which was approximately twice compared to that with only dipolar resonant excitation, and the ion unidirectional ejection efficiency could be improved to 97%. Even with a high scan rate of 6000 Da/s, there was minimal loss of mass resolution caused by increased scan rate in double resonant excitation mode. By employing the double resonant excitation method, the mass resolution could be further increased while maintaining a considerably high ion unidirectional ejection efficiency, which might be a simple and practical approach for developing a high-performance miniature ion trap mass analyzer.

Parameter characterization of variable bending stiffness module with electrostatic layer jamming based on giant electrorheological fluid

Soft grippers exhibit good adaptability, but their grasping performance is limited. Variable-stiffness technology has been applied to soft grippers to address this problem. Therefore, a variable bending stiffness module (VBSM) with electrostatic layer jamming based on a giant electrorheological fluid (ELJ-GERF) for soft robots is proposed in this study, which exhibits a faster response time and a wider range of stiffness variation. A VBSM prototype is fabricated, and a theoretical model is established. The stiffness is mainly affected by the electrode quantity, overlapping area of electrode plates, insulator and conductive layers’ thickness, medium thickness and the exciting voltage. Direct current (DC) voltage experiments and alternating current (AC) voltage experiments were conducted on the test samples of filled with air (ELJ-AIR), silicone oil (ELJ-OIL), and ELJ-GERF. The experimental result show that stiffness-regulation of the VBSM can be achieved by adjusting the exciting voltage, and AC voltage being more suitable for regulating the stiffness of the VBSM than DC voltage. For AC voltage, the stiffness of ELJ-GERF increases to 53.5 times when a 4 kV voltage is applied. The stiffness variation range is about 2 to 3 times greater than that of ELJ-AIR or ELJ-OIL. Through the stiffness characterization experiment, the stiffness of the VBSM in this study is influenced by the viscosity of the GERF and the gap between the electrode plates. Through the capacitance test, the VBSM exhibits self-sensing ability. Finally, the VBSM is applied to a soft gripper, the vibration performance and variable stiffness performance in its application are verified.

Time-resolved laser-induced fluorescence spectroscopy using CW diode laser for diagnostics of argon-ion velocity distribution near AC-biased electrode.

Controlling the ion velocity in an ion sheath by applying an alternating current (AC) voltage to an electrode and/or a substrate is critical in plasma material processes. To externally control the velocity distribution of incident ions on a substrate, the application of tailored-waveform AC voltages instead of sinusoidal voltages has garnered interest in recent years. In this study, to investigate temporal changes in ion-velocity distributions, we developed a time-resolved laser-induced fluorescence spectroscopy (LIF) system using a continuous-wave diode laser as an excitation-laser source. A time-resolved LIF system entails the capture of temporally continuous and spectrally discrete LIF spectra during an AC voltage cycle. By measuring temporal changes in the LIF signal intensity at various excitation-laser wavelengths, the argon-ion velocity distribution near the electrode following the AC voltage can be characterized. The results of applying sinusoidal, triangular, and rectangular bias waveforms indicate that the LIF measurement scheme proposed herein can be used to investigate the dynamic behavior of ion-velocity distributions controlled by tailored-waveform AC voltages.

Characterization of electric field distribution in valve-side casing of 500 kV converter transformer considering AC and DC mixed voltage

The converter transformer, as one of the indispensable core devices in the ultra-high voltage direct current (UHVDC) transmission system, exhibits highly complex electric field distribution characteristics within the valve-side bushing. In-depth research into the electric field distribution characteristics and variation patterns of the valve-side bushing under both alternating current (AC) and direct current (DC) voltage conditions is crucial for ensuring the reliable operation of the transmission system. This study focuses on investigating the electric field distribution of the valve-side bushing under AC and DC voltage excitations. A full-scale finite element model of the valve-side bushing of the converter transformer is constructed using finite element simulation software for modeling and research purposes. The results indicate that the internal electric field distribution of the bushing is generally similar under both AC and DC voltage excitations. However, in the SF6-filled region, a steeper voltage drop is observed under DC excitation compared to AC. The space charges generated in the DC electric field due to field polarization have a significant impact on the distortion of the electric field on the inner and outermost layer electrode plates. These conclusions provide theoretical guidance for the insulation design of the valve-side bushing in converter transformers at the 500 kV voltage level and similar ratings.

Structure and electrochromic properties of polypyrrole films synthesized by AC electrochemical impedance spectroscopy under different amplitude

Alternating current (AC) electrochemical impedance spectroscopy (EIS) was employed to synthesize polypyrrole (PPy) electrochromic films on fluorine-doped tin oxide (FTO) transparent conductive glasses. When depositing the PPy films, a fixed initial voltage was 700 mV and AC of different amplitudes was applied. The influence of AC voltage amplitude on the structure and electrochromic performance of PPy films was investigated. Scanning electron microscope (SEM) observation reveals that the PPy films prepared under AC are composed of uniform-distributed nanospheres when the AC amplitude is below 400 mV, which is different from the submicron structure displayed by PPy films prepared under direct current (DC). This kind of nanospherical structure is helpful to ion transport, resulting in improved electrochromic properties of the PPy films prepared under AC compared with the PPy film prepared under DC. In particular, the PPy film prepared under 100 mV amplitude AC shows ideal electrochromic properties, with an ion diffusion coefficient of 8.13 × 10−10 cm2·s−1, a coloring efficiency of 137.4 cm2·C−1, quick coloration and bleaching switching times of 5.0 s and 6.5 s, respectively, and retains 65.7% of its optical modulation after 100 cycles.

Signal Characterization in the Design of Triac and Microcontroller Based Domestic Alternating Current (AC) Voltage Stabilization System

Fluctuation in sinusoidal mains voltage is nothing but the change in magnitude of voltage, which normally exceed or goes below the steady state voltage range prescribed by some standards. This work proposes to achieve AC voltage stabilization by using feed-forward technique to apply directly the characterized mains sensor voltage which, is representative of the mains AC voltage fluctuation of 80-280V, to PIC16F877A microcontroller. The key innovation of the network is the novel ability to infer and select the triac that is connected to one of the auto-transformer tapings with an AC voltage of approximately 220V across it, as the output voltage of the stabilizer. Besides, the system also has a protective mechanism to de-select all the triacs in under/over voltage situations of 78V and 282V respectively. Comprehensive simulation and real-time results demonstrate that the proposed model achieves state-of-the-art performance on 80-280V range mains voltage fluctuations.

Formation of polymerizable layer on a photo-alignment layer of liquid crystal cell and its image sticking characteristics

The effect for polymerizable layer on a vertical-type photo-alignment layer was investigated from the point of image sticking characteristics. Fabrication process of the polymerizable layer is followings; photo-alignment treatment is firstly carried out by exposing polarized ultraviolet (UV) from the oblique direction. After construction of the liquid crystal (LC) cell, the LC material including monomers is injected, and unpolarized UV is exposed for formation of the polymerizable layer. For avoiding pretilt angle shift during the exposure, fast rate constant of polymerization is necessary, and mixed monomers 4,4’-dimethacryloyl-oxy-biphenyl (4,4’-DMABiph) and 4,4’-dimethacryloyl-oxy-benzilketal (4,4’-DMABzk) are appropriate for obtaining small level of image sticking parameters. As the image sticking parameters, residual direct current voltage (V rDC) and difference in pretilt angle (Δtilt) before and after application of alternate current voltage were evaluated, and the results of V rDC and Δtilt indicated that 6% 4,4’-DMABzk in the mixed monomers 4,4’-DMABiph and 4,4’-DMABzk would be useful for obtaining the small level of image sticking.

Label-Free Neuropeptide Detection beyond the Debye Length Limit.

Biosensors with high selectivity, high sensitivity, and real-time detection capabilities are of significant interest for diagnostic applications as well as human health and performance monitoring. Graphene field-effect transistor (GFET) based biosensors are suitable for integration into wearable sensor technology and can potentially demonstrate the sensitivity and selectivity necessary for real-time detection and monitoring of biomarkers. Previously reported DC-mode GFET biosensors showed a high sensitivity for sensing biomarkers in solutions with a low salt concentration. However, due to Debye length screening, the sensitivity of the DC-mode GFET biosensors decreases significantly during operation in a physiological fluid such as sweat or interstitial fluid. To overcome the Debye screening length limitation, we report here alternating current (AC) mode heterodyne-based GFET biosensors for sensing neuropeptide-Y (NPY), a key stress biomarker, in artificial sweat at physiologically relevant ionic concentrations. Our AC-mode GFET biosensors show a record ultralow detection limit of 2 × 10-18 M with an extensive dynamic range of 10 orders of magnitude in sensor response to target NPY concentration. The sensors were characterized for various carrier frequencies (ranging from 30 kHz to 2 MHz) of the applied AC voltages and various salt concentrations (10, 50, and 100 mM). Contrary to DC-mode sensing, the AC-mode sensor response increases with an increase in salt concentration in the electrolyte. The sensor response can be further enhanced by tuning the carrier frequency of the applied AC voltage. The optimum response frequency of our sensor is approximately 400-600 kHz for salt concentrations of 50 and 100 mM, respectively. The salt-concentration- and frequency-dependent sensor response can be explained by an electrolyte-gated capacitance model.

Structure and Dynamics of the Electrical Double Layer during the Rapid Alternating Polarity Electro-Synthesis

Conventional electrochemical organic synthesis uses direct current (DC) condition, where the electrode polarity is not changed during the operation. Unlike DC, alternating current (AC) introduces two more tunable parameters into the potential or current profile: frequency and waveform, allowing new possibilities for modulating reaction efficiency and selectivity. Several very recent AC electrosynthesis examples have shown that the AC can lead to enhanced chemoselectivity that cannot be reproduced by their DC counterparts1–3. For instance, Hayashi et al. presented a highly selective and easily scalable Birch-type reduction of heteroarenes by rapid alternating polarity (rAP) waveform3. AC voltage transforms the reaction kinetics presumably by affecting the mass transfer of reactive species both in the bulk solution and the electrical double layers (EDL). However, the mechanistic origin of the unique reactivity in AC electrosynthesis is underexplored. Molecular-level details are still in lack to possibly guide the rational design of AC reaction parameters.In this study, we have chosen the rAP heteroarene reduction as the example system and employed classical molecular dynamics (MD) simulations to reveal the liquid structure and dynamics in bulk and interfacial electrolyte. To capture the electrode-electrolyte interfaces, a slab-geometry simulation cell was used, where a 10 nm thick liquid electrolyte is sandwiched between two oppositely charged graphene surfaces. The multicomponent electrolyte was composed of ethanol and tetrahydrofuran (THF) as the co-solvent, [(CH3)4N]+[(BF4)]- as the salt, and a heteroarene substrate. Based on the charge distribution function statistics, the EDL layer was about 1 nm thick, so if any of the oxygen atom in the ethanol or THF is within 6 Å to the electrode surface, they are considered to be within the EDL. Under both AC and DC, the ethanol to THF ratio was higher than that in the bulk electrolyte due to stronger ion-ethanol attraction. The EDL structure responded to electric field polarity change at different time scales. First, the molecule orientation would flip also within the picosecond time scale after the polarity switch. By tracking the number of molecules in the EDL, we have found that the compositional fluctuation in the EDL converges in about 40 ps. Although it is the ion migration that gets directly affected by the alternating electric field, diffusion of charge-neutral molecules was also found to be accelerated under AC, according to the higher mean squared displacement calculated from the movement of all molecules of each species in the simulation box. This accelerated diffusion spans a larger length and longer time scales. A multi-scale model is proposed to describe both reaction kinetics and liquid structure dynamics simultaneously.

Distributed Characteristics of Free Metallic Particles in Flowing Transformer Oil Under DC and AC Voltages

Transformer oil is inevitably contaminated by metallic particles during manufacturing and operation, which will accumulate in the oil gap and poses a serious threat to the oil insulation in power transformer. However, the distributed characteristics of particles in oil channels will be influenced by oil flow. In this paper, a circulation flow device of transformer oil was established and the distributed characteristics of metallic particles in flowing oil were obtained under DC (direct current) and AC (alternative current) voltages respectively. It was found that particle counts between parallel plate electrodes and rod-plane electrodes would decrease monotonously with increasing flow velocities under DC application, whereas the concentration between spherically capped electrodes would increase slightly first and then decline. When the electrodes were energized by AC voltage, the reduction of the particle concentration was more significant with the addition of flow velocities. What’s more, the temporal changes of particle amount under different conditions were obtained. Then the impacts of flow velocities and applied voltages on particle distribution were discussed based on the force analysis on metallic particles.

High-Temperature Partial Discharge Characteristics of Power Module Packaging Insulation Under Square Pulse With High Dv/Dt Based on Down-Mixing Method

Partial discharge (PD) in the high voltage packaging insulation under square pulse with a high slew rate (SR or dV/dt) is one of the main causes of the power module failure, especially for wide bandgap (WBG) devices. But PD under fast square pulse at high temperatures is rarely studied and one of the critical reasons is the lack of an effective PD detection method under fast square pulses. In addition, the existing PD standard defines the PD criterion under sinusoidal alternating current (AC) situations, which is not the actual working condition of the power module. To address that, this paper proposes a down-mixing PD detection method and explores the influence of temperature on the PD characteristics of the power module packaging insulation. The results show that the partial discharge inception voltage (PDIV) decreases as the temperature increases. The PDIV under square pulse is always higher than that under AC voltage. The less the SR and the greater the pulse width (PW) of the square pulse, the lower the PDIV. Physical-based models for PDIV estimation concerning SR, PW, and temperature are proposed for industrial reference. Moreover, statistical analysis of PD magnitude, number, and occurrence phase under square pulse indicates that PD number decreases but PD magnitude increases with the increase in temperature. Higher temperature leads to PDs with large magnitudes, which may accelerate the degradation of packaging insulation.

Fine-Tuning the Characteristic of the Applied Potential To Improve AC-iEK Separations of Microparticles.

There is an immediate need for the development of rapid and reliable methods for microparticle and cell assessments, and electrokinetic (EK) phenomena can be exploited to meet that need in a low cost and label-free fashion. The present study combines modeling and experimentation to separate a binary mixture of microparticles of the same size (5.1 μm), shape (spherical), and substrate material (polystyrene), but with a difference in particle zeta potentials of only ∼14 mV, by applying direct current (DC)-biased low-frequency alternating current (AC) voltages in an insulator-based-EK (iEK) system. Four distinct separations were carried out to systematically study the effect of fine-tuning each of the three main characteristics of the applied voltage: frequency, amplitude, and DC bias. The results indicate that fine-tuning each parameter improved the separation from an initial separation resolution Rs = 0.5 to a final resolution Rs = 3.1 of the fully fine-tuned separation. The separation method exhibited fair reproducibility in retention time with variations ranging from 6 to 26% between experimental repetitions. The present study demonstrates the potential to extend the limits of iEK systems coupled with carefully fine-tuned DC-biased low-frequency AC voltages to perform discriminatory micron-sized particle separations.

Semiconductor Alternating-Current Voltage Stabilizers Designed to Improve the Quality of Electricity in 0.4-kV Digital Power-Distribution Networks

Semiconductor Alternating-Current Voltage Stabilizers Designed to Improve the Quality of Electricity in 0.4-kV Digital Power-Distribution Networks

Desain dan Simulasi Konverter Tiga Fasa AC – DC pada Pico Hydro

Pico hydropower plant is a generator engaged in the field of renewable energy, in general, the power system uses a 3-phase synchronous generator with AC voltage, in its development it can be used as a converter, by converting AC voltage to DC voltage. One of the uses of DC voltage is as so that it can be used as a battery charger or battery discharger. An AC-DC converter, also known as a rectifier, is a device for converting alternating current (AC) to direct current (DC). In general, many technologies in the industrial world utilize converters. In this paper, a simulation design of an AC-DC converter system will be made with a 230 Volt AC input with a DC voltage output. The manufacture of the converter is carried out with different gate values on the thyristors which are simulated using Simulink in MATLAB. The results of this study are in the form of analysis and mathematical calculations of the output of the AC-DC converter where from the simulation results that AC voltage can be converted to DC voltage with the working principle of the thyristor, thus the converter output results can be used in battery chargers and battery dischargers

EFFECT OF TEMPERATURE AND SOLAR IRRADIANCE ON THE PERFORMANCE OF 50 HZ PHOTOVOLTAIC WIRELESS POWER TRANSFER SYSTEM

A wireless power transfer (WPT) system transfers an alternating current (AC) power from a TC (transmitter coil) to a RC (receiver coil), using an electromagnetic field concept. Several previous reports on WPT systems were able to transmit this power, although their AC frequencies were high in some kilohertz or megahertz (kHz or MHz). These frequencies were unable to be applied directly on the AC loads or only administered to the direct current (DC) energy after rectification through a rectifier circuit. In the receiver phase, the AC power was also very low, due to the minimum voltage and current on the RC. Therefore, this study aims to determine the effects of temperature and solar irradiance on the performance of the 50 Hz photovoltaic wireless power transfer (PVWPT) system. This system is constructed by some PV modules in series connection, to achieve a required DC voltage level on the DC-DC converter and receiver phase. It also converts DC to AC voltages on the TC (transmitter coil) of an H-bridge inverter, with a receiver circuit and a magnetic relay coil positioned between the TC and RC (transmitter and receiver coil). The results showed that solar irradiance and temperature affected the performances of the PV module and PVWPT system. This indicated that higher solar irradiance increased the performance of the PVWPT system, whose maximum efficiency was achieved by positioning the magnetic relay coil between the TC and RC.