Alternating Current Electric Field Research Articles

Driving Force of Plasma Bullet in Atmospheric-Pressure Plasma

When plasma is generated by applying high-voltage alternating current (AC), the driving force of the temporally and spatially varying electric field is applied to the plasma. The strength of the driving force of the plasma at each spatial position is different because the electrons constituting the atmospheric-pressure nonequilibrium (cold) plasma move at a high speed in space. If the force applied to the plasma is accelerated only by the driving force, the plasma will be accelerated infinitely. The equilibrium between the driving force and the restricting force due to the collision between the plasma and neutral particles determines the inertial force and the drift velocity of the plasma. Consequently, the drift velocity depends on the strength of the time-averaged AC electric field. The pressure applied by the AC electric field equilibrates with the plasma pressure. From the law of conservation of energy, the pressure equilibrium is maintained by varying the drift velocity of the plasma.

Electric-Field-Directed Parallel Alignment Architecting 3D Lithium-Ion Pathways within Solid Composite Electrolyte.

It is of great significance to seek high-performance solid electrolytes via a facile chemistry and simple process for meeting the requirements of solid batteries. Previous reports revealed that ion conducting pathways within ceramic-polymer composite electrolytes mainly occur at ceramic particles and the ceramic-polymer interface. Herein, one facile strategy toward ceramic particles' alignment and assembly induced by an external alternating-current (AC) electric field is presented. It was manifested by an in situ optical microscope that Li1.3Al0.3Ti1.7(PO4)3 particles and poly(ethylene glycol) diacrylate in poly(dimethylsiloxane) (LATP@PEGDA@PDMS) assembled into three-dimensional connected networks on applying an external AC electric field. Scanning electron microscopy revealed that the ceramic LATP particles aligned into a necklacelike assembly. Electrochemical impedance spectroscopy confirmed that the ionic conductivity of this necklacelike alignment was significantly enhanced compared to that of the random one. It was demonstrated that this facile strategy of applying an AC electric field can be a very effective approach for architecting three-dimensional lithium-ion conductive networks within solid composite electrolyte.

Effect of electric field induced alignment and dispersion of functionalized carbon nanotubes on properties of natural rubber

Abstract The original equipment and method for orienting multi-walled carbon nanotubes (MWCNTs) in natural rubber (NR) by alternating current (AC) electric field were reported in the present study. MWCNTs with various volume fractions were dispersed in the mixture latex which composed of natural rubber, additives and methylbenzene. The application of AC electric field during nanocomposites curing process was used to induce the formation of aligned conductive nanotube networks between the electrodes. The aligned MWCNTs in the composites have a better orientation performance and dispersion quality than these of random MWCNTs by analyzing TEM and SEM images. The effects of MWCNTs anisotropy on thermal conductivity, dielectric properties, and dynamic mechanical properties of NR were studied. The mean value of thermal conductivity of composites loading with aligned MWCNTs was 8.67% higher than that of composites with random MWCNTs due to the anisotropy of aligned MWCNTs. The compounds with aligned MWCNTs possessed low dielectric constant, loss tangents and conductivity, namely a good insulativity. The compounds loading with aligned MWCNTs had lower loss modulus and better dynamic mechanical properties than those with random MWCNTs. This method can make full use of the high thermal conductivity of MWCNTs axis, and expand the application areas of natural rubber like conducting heat in a certain direction with a high efficiency.

Electrical Behavior and Microstructural Features of Electric Field-Assisted and Conventionally Sintered 3 mol% Yttria-Stabilized Zirconia

ZrO2: 3 mol% Y2O3 (3YSZ) polycrystalline pellets were sintered at 1400 °C and by applying an alternating current (AC) electric field at 1000 °C. An alumina sample holder with platinum wires for connecting the sample to a power supply was designed for the electric field-assisted sintering experiments. The apparent density was evaluated with the Archimedes technique, the grain size distribution by analysis of scanning electron microscopy images, and the electrical behavior by the impedance spectroscopy technique. Sintering with the application of AC electric fields to 3YSZ enhances its ionic conductivity. An explanation is proposed, based on the dissolution back to the bulk of chemical species, which are depleted at the grain boundaries, leading to an increase in the oxygen vacancy concentration. For the enhancement of the grain boundary conductivity, an explanation is given based on the diminution of the concentration of depleted chemical species, which migrate to the bulk. This migration leads to a decrease of the potential barrier of the space charge region, known to be responsible for blocking the oxide ions through the intergranular region. Moreover, the heterogeneity of the distribution of the grain sizes is ascribed to the skin effect, the tendency of the AC current density to be largest near the surface, decreasing towards the bulk.

Coalescence behavior of two water drops in viscous oil under an AC electric field

ABSTRACTElectric coalescence in alternating current (AC) electric field is one of the important electrical dehydrate technologies. In this study, the coalescence behavior of two water drops in an AC electric field was studied experimentally using a high-speed camera. There is a critical electric field strength above which the two drops would not coalescence. Such coalescence behavior was supposed to be depended on the electric field strength and the frequency. Lower electric field strength, lower frequency and smaller size would facilitate the coalescence of drops. The understanding of the electric coalescence could be helpful to advance the design of the electrocoalescencers.

Orienting lipid-coated graphitic micro-particles in solution using AC electric fields: A new theoretical dual-ellipsoid Laplace model for electro-orientation

Graphitic micro-particles are commonly coated with thin layers to generate stable aqueous dispersions for various applications. Such particles are technologically interesting as they can be manipulated with electric fields. Modeling the electrical manipulation of submerged layered micro-particles analytically or numerically is not straightforward. In particular, the generation of reliable quantitative torque predictions for electro-orientation experiments has been elusive. The traditional Laplace model approximates the coated particle by an ellipsoid with a confocal ellipsoidal layer and solves Laplace's equation to produce convenient analytical predictions. However, due to the non-uniformity of the layer thickness around the ellipsoid, this method can lead to incorrect torque predictions. Here we present a new theoretical dual-ellipsoid Laplace model that corrects the effect of the non-uniform layer thickness by calculating two layered ellipsoids, each accounting for the correct layer thickness along each relevant direction for the torque. Our model describes the electro-orientation of submerged lipid-coated graphitic micro-particles in the presence of an alternating current (AC) electric field and is valid for ellipsoids with moderate aspect ratios and coated with thin shells. It is one of the first models to generate correct quantitative electric torque predictions. We present model results for the torque versus frequency and compare them to our measurements for lipid-coated highly ordered pyrolytic graphite (HOPG) micro-flakes in aqueous NaCl solution at MHz frequencies. The results show how the lipid shell changes the overall electrical properties of the micro-flakes so that the torque is low at low frequencies and increases at higher frequencies into the MHz regime. The torque depends critically on the lipid-shell thickness, the solution conductivity and the shape of the particle, all of which can be used as handles to control the response of the particles. Our model is useful to predict the frequencies at which electro-orientation can be observed in dilute dispersions and the reduction in torque caused by the shell.

Phase equilibrium and protein partitioning in aqueous two-phase systems containing imidazolium ionic liquids and surfactant at low voltage levels

In this paper, the binodal data of aqueous two-phase system (ATPS) containing imidazolium-based ionic liquids (chlorinated 1-ethyl-3-methylimidazole, [Emim]Cl), and a non-ionic surfactant (octylphenol polyethoxylene, Triton X-100) was obtained by means of the cloud point method in the temperature intervals T=(288.15–308.15) K. It was found that the [Emim]Cl/Triton X-100 ATPS was sensitive to temperature and had a long phase segregation time. Screening experiments of various additives showed that adding 7% of sodium dodecyl sulfate (SDS) to the total mass of surfactants (w/w) reduced the temperature sensitivity, and improved the phase separation rate of the system. The liquid-liquid equilibrium (LLE) data of [Emim]Cl/Triton X-100 ATPS without additive and containing 7% SDS at 298.15K was further studied according to the cloud point method. To further shorten the long phase disengagement time, a low-voltage alternating current (AC) electric field was added to the [Emim]Cl/surfactant ATPS. Through the optimization of AC electric field conditions (such as electric field type, frequency and duty ratio), a relatively fast and stable [Emim]Cl/surfactant ATPS was established. In 0.67V/cm field strength, 1000Hz frequency and 50% duty ratio of impulse waveform, the phase splitting time is shortened by 2–3 times. With and without electric field, protein partitioning of cytochrome c (Cyt-c), bovine serum albumin (BSA) and lysozyme (Lys) in [Emim]Cl/surfactant ATPS indicated that Cyt-c and BSA tended to distribute in the bottom phase, while Lys was inclined to distribute in the top phase. The application of the AC electric field can still decrease the phase separation time in the protein distribution process, and has no significant effect on the distribution behavior of proteins. Furthermore, Lys activity in the top phase of ATPS was significantly enhanced, which could be caused by the low concentration of Triton X-100 in the top phase based on the comparison of Lys fluorescence spectra analysis in aqueous solution, in the top phase and in the bottom phase of [Emim]Cl/surfactant ATPS.

AC-Bipolar Anodization of Aluminum: Effects of Frequency on Thickness of Porous Alumina Films

The formation of porous alumina films using bipolar electrochemistry under alternating current (AC) electric fields without a direct electrical connection (“wireless treatment”) was investigated. The effect of frequency on the thickness of the films was evaluated using spectrophotometric analysis of dyed specimens and field-emission scanning electron microscopy. A film formation was simultaneously achieved on both sides of a high-purity aluminum electrode in oxalic acid under an AC electric field. A film formed at 150 Hz was thicker than those formed at other frequencies even in the same reaction time. Although the growth of non-uniform films were observed for AC-bipolar anodization, the morphology of the obtained films was roughly the same as those formed using conventional AC anodization with a direct connection, suggesting a similar oxide formation mechanism. Moreover, the dependence of film thickness on frequency was almost in agreement with the tendency observed for conventional AC anodization reported previously. The main disadvantage of AC-bipolar anodization lies in the decrease of the efficiency of film formation. From the application standpoint, however, the wireless treatment can introduce new possibilities for electrochemical surface treatment of small conductive materials that require a specific manipulation for a direct electrical connection.

Prevention of Evaporation Caused by a Rapid Immunohistochemistry Method Applying Non-contact Alternating-Current Electric-Field Mixing

It is widely recognized that pathology is the most important factor for staging and selecting effective chemotherapy for patients with cancer. Immunohistochemistry (IHC) is a reliable screening method, but intra-operative diagnosis by frozen section with IHC is not possible because IHC takes approximately 6 hours. We recently developed a rapid-IHC method that makes use of an alternating current (AC) electric field to facilitate the antigen-antibody reaction, and reported its usefulness for detection of lung cancer and breast cancer. The antibody is mixed within microdroplets as the voltage is switched on and off at specific intervals. The resultant Coulomb force stirs the diluted solution on the sections, which increases the opportunity for contact. The rapid-IHC device reduces the time required for IHC as well as the amount of antibody required for analyses. The device may also be applied for in situ hybridization (ISH); however, ISH requires a warm temperature, such as 37℃, and a longer processing time than the rapid-IHC method. Consequently, evaporation can be a problem during ISH. The aim of the present study was to evaluate the utility and reliability of an oil cover and cover cap made of polyethylene terephthalate (PET) for preventing evaporation due to the AC electric field applied to facilitate the antigen-antibody reaction. We have shown that both the oil cover and PET cover cap prevented evaporation when using the rapid-IHC device.

Electric field-induced alignment of nanofibrillated cellulose in thermoplastic polyurethane matrix

Nanofibrillated fibers (NFC) has been largely used as reinforcing filler to improve the properties of polymer matrix because of their unique properties such as high aspect ratio, good aqueous stability, high specific strength and stiffness. However, the full potential of NFC as reinforcing agent has not been realized because of its poor dispersion and random distribution in polymer matrix. In this work, we demonstrate the importance of alignment of NFC to determine the mechanical properties of polymer via applying alternative current (AC) electric field and using thermoplastic polyurethane (TPU) as the matrix. The TPU/NFC nanocomposites were prepared via solution casting method and the effect of parameters of the applied electric field (amplitude, frequency as well as the duration of application) on the orientation degree of NFC and the final properties of TPU/NFC nanocomposites are systematically investigated. It was found that NFC could be easily oriented under effect of AC due to electric induced polarization. The prepared anisotropic TPU/NFC composites exhibit 2.07 and 1.82 times increase of tensile strength and elongation at break in the parallel direction than that in the vertical direction for the anisotropic samples, respectively. It was also interesting, to find that the samples with aligned NFC exhibit an increased dielectric constant with lower dielectric loss, which could provide an idea to fabricate high performance dielectric materials.

Dielectric Spectroscopy of Localized Electrical Charges in Ferrite Thin Film

A thin film of Gd-doped Mn-Cr ferrite has been prepared by pulsed laser deposition from a bulk sample of the same ferrite prepared by the conventional double sintering ceramic technique. The charge localization and surface conduction in the ferromagnetic thin film were studied. The relaxation of the dielectric dipoles after exposure to an external alternating-current (AC) electric field was investigated. The effect of charge localization on the real and imaginary parts of the dielectric modulus was studied. The charge localization in the thin film was enhanced and thereby the Maxwell–Wagner-type interfacial polarization. The increase in interfacial polarization is a direct result of the enhanced charge localization. The sample was characterized in terms of its AC and direct-current (DC) electrical conductivity, and thermally stimulated discharge current.

Electrodeformation of multi-bilayer spherical concentric membranes by AC electric fields

It is now well established that external stresses alter the behaviour of cells, where such alterations can be as profound as changes in gene expression. A type of stresses of particular interest are those due to alternating-current (AC) electric fields. The effect of AC fields on cells is still not well understood, in particular it is not clear how these fields affect the cell nucleus and other organelles. Here, we propose that one possible mechanism is through the deformation of the membranes. In order to investigate the effect of AC fields on the morphological changes of the cell organelles, we modelled the cell as two concentric bilayer membranes. This model allows us to obtain the deformations induced by the AC field by balancing the elastic energy and the work done by the Maxwell stresses. Morphological phase diagrams are obtained as a function of the frequency and the electrical properties of the media and membranes. We demonstrate that the organelle shapes can be changed without modifying the shape of the external cell membrane and that the organelle deformation transitions can be used to measure, for example, the conductivity of the nucleus.

Effects of electric field and bias voltage on corrosion behavior of tin under a thin electrolyte layer

The effects of electric field and bias voltage on corrosion behavior of tin under a thin electrolyte layer (TEL) were investigated by electrochemical and surface techniques. The results indicated that the order of the corrosion rate of tin under different electric fields with the same electric field gradient was as follows, square wave alternating current electric field (ACEF)>sinusoidal wave ACEF>direct current electric field (DCEF)>blank. Moreover, the corrosion rate of tin increased with increased direct current bias voltage under different electric fields. The contributions of electric field gradient and leakage current to the corrosion rate of tin were quantified under different electric fields with different bias voltages.

Emitter Spacer Layers Influence on the Dynamic Characteristics of Resonant-Tunneling Diode

Within the framework of the coherent quantum-mechanical model, which is based on the solution of the time-dependent Schrodinger equation with exact open boundary conditions, we have numerically analyzed the behavior of the InGaAs/AlAs resonant-tunneling diode (RTD) in an alternating-current electric field in the presence of spacer layers. It is shown that the interaction of the energy levels in a quantum well of the RTD, and the same in a quantum well of the emitter spacer, leads to splitting of these levels, which sharply increases the active current of RTD. In this case, the value of the active current at the finite frequencies may exceed the active current within the low-frequency limits. For RTD, heterostructure considered active current at frequency 1.77 THz takes its maximum value at the thickness of the emitter spacer equals to 6.5 nm exceeding the corresponding value in the absence of the spacer by the factor of 32. The results obtained in this paper may be useful to improve the frequency characteristics of resonant-tunneling nanostructures.

Dynamics of a Leidenfrost Droplet Modulated by Electrowetting

Leidenfrost phenomenon is closely related to film boiling and the critical heat flux (CHF) limit of boiling heat transfer. Understanding the mechanisms of Leidenfrost phenomenon and devising effective ways to suppress it is of great interest to the heat transfer enhancement community. In this work, a synchronized high-speed optical imaging and infrared (IR) thermography approach was employed to investigate the dynamics of a Leidenfrost droplet under the influence of electrowetting (EW). The Leidenfrost droplet was produced by dispensing a water drop on a Teflon-coated silicon wafer maintained at a wall temperature of Twall = 200 °C. Both direct-current (DC) and alternating-current (AC) electric fields were applied to induce EW effect to suppress the Leidenfrost state. The interfacial instabilities of the Leidenfrost droplet were observed, and the instantaneous temperature and heat flux distributions on the heating surface were measured. The results suggest that the electrical forces destabilize the liquid-vapor interface and cause the vapor film that insulates the heating surface from the droplet to collapse. Re-establishment of the liquid-solid contact helps to drastically improve the heat transfer, as evidenced by the reduced surface temperature and the enhanced heat flux.

Electric-Field Assisted Assembly of Colloidal Particles into Ordered Nonclose-Packed Arrays.

Nonclose-packed colloidal arrays have many potential applications ranging from plasmonic sensors, light trapping for photovoltaics, to transparent electrodes. However, scalable fabrication of those structures remains a challenge. In this Article, we investigate the robustness of an electric-field assisted approach systematically. A monolayer of nonclose-packed crystalline array is first created under a low-frequency alternating-current electric field in solution. We then apply a sequence of direct-current pulses to fix the particle array onto the substrate so that it remains intact even after both field removal and solvent evaporation. Key process parameters such as the alternating-current field strength, direct-current magnitude, particle concentration, and solvent-evaporation rate that affect both ordering and fixing of colloidal particles have been studied systematically. We find that direct currents with an intermediate magnitude induce electrophoretic motion of particles toward the substrate and facilitate their permanent adhesion on the substrate due to strong van der Waals attraction. A higher current, however, causes lateral aggregation of particles arising from electroosmotic flow of solvent and destroys the periodic ordering between particles. This approach, in principle, can be conveniently adapted into the continuous convective assembly process, thus making the fabrication of nonclose-packed colloidal arrays scalable.

AC Electroluminescent Processes in Pr3+-Activated (Ba0.4Ca0.6)TiO₃ Diphase Polycrystals.

We investigated the properties of alternating current (AC)-driven electroluminescence from (Ba0.4Ca0.6)TiO3:Pr3+ diphase polycrystal-based device. The results of crystal phases and micrographs, and the symmetrical dual emissions in one AC cycle, indicate the spontaneous formation of a dielectric/phosphor/dielectric sandwich microstructure in (Ba0.4Ca0.6)TiO3:Pr3+. The electroluminescent device emits a red light of 617 nm, which is attributed to the 1D2-3H4 transition of Pr3+ in the phosphor phase. At a fixed AC frequency, the intensity of electroluminescence exhibits a steep enhancement when applying an increased driving electric field that is beyond a threshold. In a fixed driving electric field, the intensity of electroluminescence shows a rapid rise at low frequencies, but reaches saturation at high frequencies. Based on a double-injection model, we discussed systematically the electroluminescent processes in a whole cycle of AC electric field, which matched well with the experimental data. Our investigation is expected to expand our understanding of such a diphase electroluminescent device, thereby promoting their applications in lighting and displays.

A theory of the inverse magnetoelectric effect in layered magnetostrictive–piezoelectric structures

A theory of the inverse magnetoelectric effect in layered structures has been presented. The theory is based on solving the equations of elastodynamics and electrostatics separately for the magnetostrictive and piezoelectric phases, taking into account the conditions at the interface between the phases. Expressions for the coefficient of inverse magnetoelectric conversion through the parameters characterizing the magnetostrictive and piezoelectric phases have been obtained. Theoretical dependences of the inverse magnetoelectric conversion coefficient on the frequency of the alternating-current electric field for the three-layer PZT–Ni–PZT structure and the two-layer terfenol-D–PZT structure have been calculated. The results of the calculations are in good agreement with the experimental data.

Capacitive DNA sensor for rapid and sensitive detection of whole genome human herpesvirus-1 dsDNA in serum.

This work presents a rapid, highly sensitive, low-cost, and specific capacitive DNA sensor for detection of whole genome human herpesvirus-1 DNA. This sensor is capable of direct DNA detection with a response time of 30s, and it can be used to test standard buffer or serum samples. The sensing approach for DNA detection is based on alternating current (AC) electrokinetics. By applying an inhomogeneous AC electric field on sensor electrodes, positive dielectrophoresis is induced to accelerate DNA hybridization. The same applied AC signal also directly measures the hybridization of target with the probe on the sensor surface. Experiments are conducted to optimize the AC signal, as well as the buffers for probe immobilization and target DNA hybridization. The assay is highly sensitive and specific, with no response to human herpesvirus-2 DNA at 5ng/mL and a LOD of 1.0pg/mL (6.5 copies/μL or 10.7aM) in standard buffer. When testing the double stranded (ds) DNA spiked in human serum samples, the sensor yields a LOD of 20.0pg/mL (129.5 copies/μL or 0.21 femtomolar (fM)) in neat serum. In this work, the target is whole genome dsDNA, consequently the test can be performed without the use of enzyme or amplification, which considerably simplifies the sensor operation and is highly suitable for point of care disease diagnosis.

Fibrillar disruption by AC electric field induced oscillation: A case study with human serum albumin

The effect of oscillation induced by a frequency-dependent alternating current (AC) electric field to dissociate preformed amyloid fibrils has been investigated. An electrowetting-on-dielectric type setup has been used to apply the AC field of varying frequencies on preformed fibrils of human serum albumin (HSA). The disintegration potency has been monitored by a combination of spectroscopic and microscopic techniques. The experimental results suggest that the frequency of the applied AC field plays a crucial role in the disruption of preformed HSA fibrils. The extent of stress generated inside the droplet due to the application of the AC field at different frequencies has been monitored as a function of the input frequency of the applied AC voltage. This has been accomplished by assessing the morphology deformation of the oscillating HSA fibril droplets. The shape deformation of the oscillating droplets is characterized using image analysis by measuring the dynamic changes in the shape dependent parameters such as contact angle and droplet footprint radius and the amplitude. It is suggested that the cumulative effects of the stress generated inside the HSA fibril droplets due to the shape deformation induced hydrodynamic flows and the torque induced by the intrinsic electric dipoles of protein due to their continuous periodic realignment in presence of the AC electric field results in the destruction of the fibrillar species.