Applied AC Voltage Research Articles

Reentrant prewavy instability in competition between rising and twist modes in ac field-driven electroconvection.

We report on the prewavy (PW) instability in ac field-driven electrohydrodynamics that is induced in a nematic liquid crystal (NLC) sandwiched between parallel electrodes. The instability is characterized by a twist mode of the NLC director along the vertical orientation to the electrodes (i.e., the z axis), generating a periodic pattern having a large wavelength (λ_{PW}) in the xy plane. The PW periodic to the preferred director n_{0} of the NLC should be distinguished from well-known electroconvection (EC) such as normal rolls (NRs) and abnormal rolls (ARs) with similar wave vectors. A reentrant PW (PW2) was discovered by employing well-adjusted optical conditions and a dynamic image-process method. The wavelength λ_{PW2} of the PW2 accompanying turbulent EC was measured as functions of the applied ac voltage and frequency, which was distinguished from λ_{PW1} of the primary PW (PW1) separated from the NR. Moreover, the appearance, disappearance, and reappearance of the PW were investigated for five frequency regions classified in the ac field-driven EC; it was found that the high frequency and high voltage causes competition between the rising mode (θ, tilting angle to the xy plane) and twist mode (ϕ, in-plane angle to the x axis) of the director through electrohydrodynamic coupling between the director field and flows. We discuss how the PW2 can arise by considering another twist mode known as AR instability.

Observation and Simulation for the Movement of Metallic Particles in Flowing Transformer Oil under AC/DC and Combined Voltages

The movement of metallic particles in flowing transformer oil is observed under AC, DC and AC/DC combined voltages. It is found that the particles execute sedimentation followed by repeated up-down motions in the vertical direction, and meanwhile move along with the oil flow in the horizontal direction. The up-down motion is affected by applied voltage. With the application of AC voltage, the bounce height from the grounded electrode does not exceed the half of electrode separation. After the DC component is introduced, the particles can arrive at the high-voltage electrode. When the ratio of combined voltage between AC and DC components is 1:1, the particles drop slightly in the upward motion and rise slightly in the downward motion. As the ratio is reduced, no such slightly dropping or rising is observed. In order to analyze the experimental results, a simulation model about solid-liquid two-phase flow subjected to electric field is constructed. Simulated trajectories of particles are in good agreement with the experiments. Based on the model, the evolution of force condition exerted on a particle during its motion is analyzed, and the relationship between partial discharge (PD) frequency and particle movement is briefly discussed.

Monitoring of the Electrototation of Cells Stimulated By the Ionophore

Monitoring of the Electrototation of Cells Stimulated By the Ionophore

Soft bidirectional haptic I/O module based on bi-convex patterned PVC gel

In this paper, we propose a bidirectional soft haptic I/O module that not only senses the haptic force but also generates a mechanical vibrotactile sensation. Under external pressure, the distance between the moving plate and lower electrode layer decreases, and the bi-convex patterned poly vinyl chloride (bpPVC) gel gets compressed. These two motions make the capacitance of the proposed module change. Moreover, the application of external electric field (EF) creates an electrostatic force between the upper and lower electrode layers and generates the electric-field-induced deformation of the bpPVC gel simultaneously. As soon as the external EF disappears, the proposed module regains its original shape through the elastic restoring forces of the bpPVC gel and planar springs. Therefore, the applied AC voltage makes the proposed module vibrate. The dielectric and mechanical properties of the bpPVC gel are measured to investigate the optimal weight ratio of the PVC and plasticizers. Experiments are conducted to measure the haptic sensing and actuating performance of the proposed method. The capacitance of the proposed haptic I/O module increases from 17.4 pF to 54.8 pF when the external pressure varied from 0 kPa to 100 kPa. On the other hand, the haptic output of the proposed I/O module is observed as 0.81g (g = 9.8 m s−2) at 100 Hz. The results clearly indicate that the proposed haptic I/O module not only senses the static and dynamic pressure but also controls the amplitude of vibrotactile sensation. Owing to its mechanically soft structure, we expect that the proposed haptic I/O module has the potential to be applied or attached to various flexible/soft devices or the human body.

Charging potential measurement of floating electrode modeled on the arc shield of vacuum interrupter under AC voltage application

AbstractA charging potential of a floating electrode modeled on vacuum interrupter was measured under unipolar AC voltage application using a surface potential meter. As a result, when a lower voltage was applied to the samples, only an induced potential depending on the electrostatic capacities of the sample and surrounding objects around the sample was measured from the floating electrode. However, in the case of high voltage application, not only induced voltage but also a positive charging potential was observed from the floating electrode which was enough to change the potential of the floating electrode. This is due to the field electron emission from the floating electrode itself.

Charging Potential Measurement of Floating Electrode Modeled on the Arc Shield of Vacuum Interrupter under AC Voltage Application

Charging Potential Measurement of Floating Electrode Modeled on the Arc Shield of Vacuum Interrupter under AC Voltage Application

Electrochemical top-down synthesis of C-supported Pt nano-particles with controllable shape and size: Mechanistic insights and application

In this work, we demonstrate the power of a simple top-down electrochemical erosion approach to obtain Pt nanoparticle with controlled shapes and sizes (in the range from ~ 2 to ~ 10 nm). Carbon supported nanoparticles with narrow size distributions have been synthesized by applying an alternating voltage to macroscopic bulk platinum structures, such as disks or wires. Without using any surfactants, the size and shape of the particles can be changed by adjusting simple parameters such as the applied potential, frequency and electrolyte composition. For instance, application of a sinusoidal AC voltage with lower frequencies results in cubic nanoparticles; whereas higher frequencies lead to predominantly spherical nanoparticles. On the other hand, the amplitude of the sinusoidal signal was found to affect the particle size; the lower the amplitude of the applied AC signal, the smaller the resulting particle size. Pt/C catalysts prepared by this approach showed 0.76 A/mg mass activity towards the oxygen reduction reaction which is ~ 2 times higher than the state-of-the-art commercial Pt/C catalyst (0.42 A/mg) from Tanaka. In addition to this, we discussed the mechanistic insights about the nanoparticle formation pathways.

A MEMS-based methodology for measurement of effective density and viscosity of nanofluids

Due to the importance of the usage of nano-technology based fluids in several industrial processes, the presented research deals with mathematical modeling of a comb-drive MEMS-based sensor for determinations of the physical properties of nanofluids. The proposed sensor is made up of a driving comb, sensing comb, and a sensing plate. It is actuated longitudinally via the electrostatic force created by applying an AC voltage to the driving section of the sensor. The coupled equations of the vibration of the lumped dynamic mass and the nanoscale fluid field have been derived and solved simultaneously. Frequency analysis of the dynamic model indicates that a nanofluid has inertial and damping effects on the longitudinal vibration of the structure. Therefore, the viscosity and density of a nanofluid can be measured simultaneously via the detection of the resonance frequency and resonance amplitude changes of the structure. The practical restrictions of the applied AC voltage for the linear dynamic behavior of the structure have also been presented.

Local piezoelectric properties in Na-flux GaN bulk single crystals

The local piezoelectricity of a Na-flux GaN crystal grown on a multipoint-seed-GaN template is investigated using piezoresponse force microscopy. The piezoresponse is critically dependent on two types of growth regions that are dominantly formed in the Na-flux GaN crystal: the c-growth sector (cGS), which is grown on top of the point-seed GaN surface with a growth front of (0001) planes, and the facet-growth sector (FGS), which is grown on the side of cGS with {101¯1} facets. Quantitative analyses reveal the GaN surface displacements at cGS that result from the piezoresponses increase with the applied AC voltage: the measured values well reflect the piezoelectric constant of d33 in GaN. The piezoresponses at the FGS and the boundary between the cGS and FGS are less sensitive than that at the cGS. A combination of cathodoluminescence and multiphoton excitation photoluminescence techniques clarifies that a local reduction of the piezoresponse observed in cGS is attributed to microscale FGSs that exist randomly in cGS. The dependence of the piezoresponse on the growth regions is quantitatively discussed from three possible viewpoints that potentially affect the polarization properties of GaN: residual strain, local crystallographic tilting, and inherent carrier distribution. As a result, a carrier screening effect is the most probable candidate to induce reduction of the piezoresponse in the FGSs of GaN crystals.

Multifunctionalities of 2D MoS2 self-switching diode as memristor and photodetector

Self-switching diodes (SSD) were fabricated at the wafer level on a 2D few-layer MoS 2 thin film (7 monolayers) grown on a 4-inch Al 2 O 3 /high-resistivity silicon wafer via Chemical Vapor Deposition (CVD). We report here that MoS 2 behaves as a transparent piezoelectric material in the near infrared spectral region and as a strain-induced ferroelectric material with a measured d 33 piezoelectric coefficient of 3–10 pm/V depending on the applied AC voltage. Moreover, we demonstrate experimentally that the SSDs behave as lateral memristors and as photodetectors in the visible spectrum, with responsivities as high as 17 A/W.

Effect of core metal on flame spread and extinction for horizontal electrical wire with applied AC electric fields

The effect of metal core on flame spread behavior over polyethylene (PE)-insulated electrical wire was experimentally investigated by varying applied AC voltage (VAC) and frequency (fAC). The present experimental results with Cu-core were compared with those conducted previously with NiCr-core. Flame spread rate (FSR) with Cu-core for the baseline case with no electric field was larger than that with NiCr-core. Both FSR and flame size were appreciably influenced by applied AC electric fields and behaved differently for Cu- and NiCr-cores. For Cu-core, FSR behavior could be classified into four regimes as fAC increases: increasing FSR (regime I), decreasing FSR (II), and again increasing FSR (III) and decreasing FSR (IV). While for NiCr-core, it has been categorized into two regimes I and II. FSR behavior was qualitatively similar to that of flame width in regimes I, II, and IV. While such a relationship was not satisfied in regime III, which can be attributed to the formation of molten PE film in the burnt wire side as well as the formation of globular molten PE in front of spreading flame edge, emphasizing the important role of complex molten PE behavior. Molten PE dripping was observed for NiCr-core, while for Cu-core, such dripping was not observed. Electrospray and di-electrophoresis phenomena occurred with Cu-core along with a formation of molten PE film on the burnt wire side via continuous di-electrophoresis phenomenon from molten PE droplet. When the frequency was excessive, flame extinction occurred via two routes: appreciable reduction of flame size (both for Cu- and NiCr-cores) and detachment of molten PE (for Cu-core). These extinction frequencies were correlated well with the voltage.

Influence of Ge4+ doping on photo- and electroluminescence properties of ZnGa2O4

Nanocrystalline ZnGa2O4 samples doped with varying concentrations of Ge4+ ions were prepared and their photo- and electroluminescence properties were investigated in detail before and after annealing at 900 °C. X-ray diffraction (XRD) studies confirmed that Ge4+ doping even to a level of 0.5 at.% at the expense of Ga3+ in ZnGa2O4, leads to incorporation of significant extent Ga3+ ions (∼29%) at Zn2+ site (tetrahedral site) in ZnGa2O4 lattice thereby increasing relative extent of distorted gallium-oxygen (GaOx) structural units. XRD, UV-Visible optical reflectance and lifetime measurements confirmed that a maximum of 0.65 at.% Ge4+ is doped in nanocrystalline ZnGa2O4. Observed blue shift in photoluminescence maximum and decrease in line width with Ge4+ doping is explained based on increased electro-negativity of Ge4+ compared to Ga3+ and lack of formation of oxygen vacancies particularly for 900 °C annealed samples. Lack of oxygen vacancies in Ge4+ doped annealed samples facilitates selective excitation of regular GaO6 and GaOx structural units, upon application of AC voltages, leading to around 50% reduction in line width of electroluminescence peak from doped sample compared to undoped one. Observed variation in electroluminescence properties between doped and undoped samples have been understood based on difference in nature of defects generated in the lattice.

Dynamic Response of Alternating-Current-Driven Light-Emitting Diodes Based on Hybrid Halide Perovskites

In this work, we report the dynamic response of alternating-current-driven light-emitting diodes based on a range of hybrid halide perovskites. Electroluminescence (EL), which appears only in the positive section of a dc voltage, arises in both cycles under a sinusoidal ac voltage. Appearance of EL emission in negative cycles of the ac voltage is explained in terms of available residual charges injected in the previous positive cycle of the sinusoidal voltage; the relative intensity of EL emission in the negative cycle can be correlated to the ambipolarity of charge carriers in the ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{Pb}\mathrm{Br}}_{x}{\mathrm{I}}_{3\text{\ensuremath{-}}x}$ series. At low frequencies of the ac voltage, the dynamic response of EL emission in any cycle is in phase with the applied ac voltage; interestingly, the EL emission starts to lag the sinusoidal voltage at higher frequencies. The phase lag also has a correlation to the ambipolarity of the active perovskite material. Finally, the frequency dependence of EL emission under an ac voltage provides the limiting frequency of device operation (\ensuremath{-}3 dB frequency) and thereby the effective carrier mobility in the active heterostructure.

Analysis and Design of a Double Fuzzy PI Controller of a Voltage Outer Loop in a Reversible Three-Phase PWM Converter

Aiming at the application of a reversible three-phase pulse width modulation (PWM) converter with a wide range of AC side voltage and DC side voltage, a double fuzzy proportional integral (PI) controller for voltage outer loop was proposed. The structures of the proposed controller were motivated by the problems that either the traditional PI controller or single fuzzy PI controller cannot achieve high performance in a wide range of AC and DC voltage conditions. The presented double fuzzy controller studied in this paper is a sub fuzzy controller in addition to the traditional fuzzy PI controller; in particular, the sub fuzzy controller can get the auxiliary correction of PI control parameters according to the AC side voltage and the DC side given voltage variation of PWM converter after the reasoning of the sub fuzzy controller, while the traditional fuzzy PI controller outputs the correction of PI control parameters according to the DC voltage error and its error change rate. In this paper, the traditional fuzzy PI controller can be called the main fuzzy controller, and the adaptive adjustment of PI control parameters of the voltage outer loop is the sum of the PI parameter correction output by the main fuzzy controller and the auxiliary PI parameter correction output by the sub fuzzy controller. Finally, the experimental results show that the reversible three-phase PWM converter can achieve excellent dynamic and static performance in a wide range of AC voltage and DC voltage applications by using the proposed double fuzzy PI controller.

Characterization of Human Glioblastoma versus Normal Plasma-Derived Extracellular Vesicles Preisolated by Differential Centrifugation Using Cyclical Electrical Field-Flow Fractionation.

Although many properties for small extracellular vesicles (sEVs, formerly termed "exosomes") isolated at ∼100 000g are known, a wide range of values are reported for their electrophoretic mobility (EM) measurements. This paper reports for the first time the effect of dilution on the EM of U87 glioblastoma cell-derived and plasma-derived sEVs and medium size EVs (mEVs, commonly termed "oncosomes") preisolated by differential centrifugation. Furthermore, the effect of resalting on the EM of sEVs and mEVs was evaluated. The EM of U87 sEVs and U87 mEVs showed an increase as the salt concentration decreased to 0.005% of the initial salt concentration. However, for the plasma sEVs and plasma mEVs, the electrophoretic mobility increased as the salt concentration decreased to 0.01% of the initial salt concentration and then increased to its initial value when the salt concentration decreased to 0.005% of the initial salt concentration. For both U87 and plasma sEVs and mEVs, the EM remained almost constant when the concentration of the particles changed and the salt concentration was kept the same as its initial value. This indicates that the EM of EVs is only a function of the salt concentration of the buffer and is independent of the concentration of the particles. The sEVs and mEVs were separated with cyclical ElFFF for the first time. The results indicate that ElFFF was able to fractionate the EVs, and a crescent-shaped trend was found for the retention time when the applied AC voltage was altered (increased).

Alignment Effect on the Piezoelectric Properties of Ultrathin Cellulose Nanofiber Films.

This study aims at evaluating the piezoelectric property of an ultrathin cellulose nanofiber (CNF) film in a thickness direction. Cellulose is known to have piezoelectric properties. However, its measurement is not easy. By making an ultrathin CNF film and eliminating space charges, the pure piezoelectric property of CNF is intended to be measured. A 600 nm thick ultrathin CNF film was prepared using a microfabrication process. The effect of alignment methods on the piezoelectric property of the ultrathin CNF film in the thickness direction was investigated with the three alignment methods: corona poling, electrical in-plane alignment, and high magnetic field (HiMA) alignment. Piezoresponse force microscopy (PFM) was utilized to analyze the piezoelectric property. By applying AC voltages using PFM, the vertical displacement on the ultrathin CNF film surface was recorded and converted into the piezoelectric coefficient, d33. The aligned ultrathin CNF films show different piezoelectric coefficients. The corona-poled ultrathin CNF film shows the largest piezoelectric coefficient among the three alignment methods. Water contact angle measurement proves that the piezoelectric constant in the thickness direction is associated with hydroxyl groups in cellulose chains appearing on the surface of the ultrathin CNF films.

Controlling the rf phase error induced micromotion in Paul trap

Excess micromotion of trapped ions leads to several adverse effects, such as modulating the absorption spectrum, shifting the transition frequency, and causing extra motional heating of ions. Moreover, it is hard to deal with, if there is no rf null point in a Paul trap. In this paper, two methods are proposed to control these adverse effects introduced by excess micromotion. The first method can eliminate the spectral modulation effect while keeping the micromotion unaffected by phase modulating the related laser. The second one can control the amplitude of micromotion or compensate it completely to remove the frequency shift effects by applying ac voltage to the dc electrodes. With these two methods, we are not only able to control the micromotion amplitude in a Paul trap without rf null point, but also to realize effective sideband cooling and quantum state manipulating when ions still undergo large excess micromotion.

Characteristics of the Partial Discharge in the Development of Conductive Particle-Initiated Flashover of a GIS Insulator

Conductive particles are one of the most important defects which can greatly degrade the performance of gas-insulated metal-enclosed switchgear (GIS). Many efforts have been made to clarify the influence on the withstand voltage, understand the flashover mechanism, and build a comprehensive model to describe the particle-initiated flashover. In this study, a partial discharge (PD) signal detected through a photomultiplier (PMT) and recorded by a high-speed data acquisition (DAQ) system was used to analyze the discharge development of a conductive particle-contaminated GIS insulator under constant high AC voltage. An additional PMT was used as a reference to eliminate the dark count of the PMT and the data collection method of a DAQ system was optimized to capture the pulse waveform of each PD to obtain detailed physical information. Spectra of the PD pulse amplitude over pulse width, PD counts within various amplitude ranges over time and phase resolved partial discharge (PRPD) patterns of the PDs in different stages are obtained through the captured PD waveforms. Characteristics of the PDs from the application of the high AC voltage up to the flashover of the insulator were then analyzed, and it was found that the features of the PDs in the near-flashover stage were significantly different to the previous stages.

Scalable Parallel Manipulation of Single Cells Using Micronozzle Array Integrated with Bidirectional Electrokinetic Pumps.

High throughput reconstruction of in vivo cellular environments allows for efficient investigation of cellular functions. If one-side-open multi-channel microdevices are integrated with micropumps, the devices will achieve higher throughput in the manipulation of single cells while maintaining flexibility and open accessibility. This paper reports on the integration of a polydimethylsiloxane (PDMS) micronozzle array and bidirectional electrokinetic pumps driven by DC-biased AC voltages. Pt/Ti and indium tin oxide (ITO) electrodes were used to study the effect of DC bias and peak-to-peak voltage and electrodes in a low conductivity isotonic solution. The flow was bidirectionally controlled by changing the DC bias. A pump integrated with a micronozzle array was used to transport single HeLa cells into nozzle holes. The application of DC-biased AC voltage (100 kHz, 10 Vpp, and VDC: −4 V) provided a sufficient electroosmotic flow outside the nozzle array. This integration method of nozzle and pumps is anticipated to be a standard integration method. The operating conditions of DC-biased AC electrokinetic pumps in a biological buffer was clarified and found useful for cell manipulation.

Electrical modeling of dielectric barrier discharge considering surface charge on the plasma modified material**Project supported by the National Key R&D Program of China (Grant No. 2018YFB0904400), the National Natural Science Foundation of China (Grant No. 51977187), the “Science and Technology Innovation 2025” Key Project of Ningbo City, China (Grant No. 2018B10019), the Natural Science Foundation of Zhejiang Province, China (Grant

We present the variations of electrical parameters of dielectric barrier discharge (DBD) when the DBD generator is used for the material modification, whereas the relevant physical mechanism is also elaborated. An equivalent circuit model is applied for a DBD generator working in a filament discharging mode, considering the addition of epoxy resin (EP) as the plasma modified material. The electrical parameters are calculated through the circuit model. The surface conductivity, surface potential decay, trap distributions and surface charge distributions on the EP surface before and after plasma treatments were measured and calculated. It is found that the coverage area of micro-discharge channels on the EP surface is increased with the discharging time under the same applied AC voltage. The results indicate that the plasma modified material could influence the ignition of new filaments in return during the modification process. Moreover, the surface conductivity and density of shallow traps with low trap energy of the EP samples increase after the plasma treatment. The surface charge distributions indicate that the improved surface properties accelerate the movement and redistribution of charge carriers on the EP surface. The variable electrical parameters of discharge are attributed to the redistribution of deposited surface charge on the plasma modified EP sample surface.