Alternating Current Electric Field Research Articles

Propagation of periodic director and flow patterns in a cholesteric liquid crystal under electroconvection

The electroconvection of liquid crystals is a typical example of a dissipative structure generated by complicated interactions between three factors: convective flow, structural deformation, and the migration of charge carriers. In this study, we found that the periodic structural deformation of a cholesteric liquid crystal propagates in space, like a wave, under an alternating-current electric field. The existence of convection and charge carriers was confirmed by flow-field measurements and dielectric relaxation spectroscopy. Given that the wave phenomenon results from electroconvection, we suggest a possible model for describing the mechanism of wave generation. The validity of the model was examined using the Onsager variational principle. Consequently, it was suggested that wave generation can be described by four effects: the electrostatic potential, mixing entropy, anisotropic friction due to charge migration, and viscous dissipation of the liquid crystal.

Modulating droplet electrohydrodynamics via the interplay of extensional flow and an alternating current electric field

Electric fields can be used to exert controlled time-varying forces on a droplet under progressive stretching in an extensional flow, allowing for its precise manipulation in various industrial and scientific applications, including microfluidics, materials science, and biological studies. However, the interaction between the combined extensional flow field and electric field may trigger a complex electrohydrodynamic response, as determined primarily by the capillary and viscous forces and the convection of surface charge. Here, we theoretically and computationally analyze the deformation and breakup of a droplet subjected to an alternating current (AC) electric field and uniaxial extensional flow. Our asymptotic theory, applicable in the small-deformation limit, quantifies the contributions of each applied field to the shape oscillations. Numerical simulations are employed to explore the dynamical evolution of the droplet in the nonlinear regime of variation in the capillary number. Our theoretical and numerical results are in excellent agreement, demonstrating that an AC electric field can significantly alter transient deformation depending on its magnitude and frequency. We identify the threshold frequency, dependent on the ratios of electrical properties, which can induce periodic oblate-prolate shape transitions. The interaction between viscous and electric stresses driving these transients is discussed. Contrary to intuition, strong electric fields greatly suppress shape oscillations, leading instead to large continuous elongations that eventually result in an end-pinching breakup mode, forming elongated bulbous-ended droplets. The breakup state, characterized by droplet length and shape at the onset of breakup, is determined by the field parameters and the physical properties of the fluids. Notably, the breakup state length and total breakup time have a non-monotonic relationship with the applied electric field frequency. The insights gained into the physics of oscillatory stable deformation and non-oscillatory unstable deformation offer new means of droplet manipulation in droplet-based micro-mechano-electrical systems that remained unexplored thus far.

AC electric field-induced changes in viscosity of aqueous ceramic suspensions and tuning of freeze-cast microstructure and compressive strength

A systematic parametric study was conducted on alternating current (AC) electric field-assisted freeze-casting to enable a comprehensive understanding of tuning freeze-cast microstructure and compressive strength and provide insights into the role of AC field. A novel finding was that the AC field increased the viscosity of aqueous ceramic suspensions, where the viscosity increase was dependent on the ceramic loading of suspensions, dispersant concentration, and field duration. Viscosity increased with field duration for a fixed solid loading and dispersant concentration. It was suggested that AC field-induced dielectrophoretic (DEP) forces decreased interparticle distances and increased interparticle interactions in ceramic suspensions, hence viscosity. It was revealed that the increase in viscosity of ceramic suspensions due to the AC field could be reversed. It was demonstrated that simple magnetic stirring of the suspensions previously subjected to an AC field (which increased viscosity) reduced viscosity to the level of the as-prepared suspensions. For materials fabrication, an AC electric field was applied to aqueous ceramic suspensions for the desired duration, then turned OFF, followed by freeze-casting, which remarkably influenced freeze-cast sintered microstructure. The impact of the field on microstructure increased with solid loading, dispersant concentration, and field duration, and microstructure changes were associated with viscosity of suspensions prior to freeze-casting. With increasing viscosity, freeze-cast microstructure became increasingly dendritic, i.e., bridge density increased. A positive correlation was observed between bridge density and compressive strength for all the materials. Depending on the solid loading, dispersant concentration, and field duration, about 5- to 8-fold increase in strength was achieved.

Mechanisms of the structures and antioxidant activity of broad bean protein affected by AC electric field: changes in conformation and molecular interaction

SummaryThe hierarchical structure modification and antioxidant traits of broad bean protein (BBP) with low denaturation induced by alternating current electric field (ACEF) were examined. The ultraviolet, Fourier transform infrared, and Raman spectrometry showed that ACEF affected the tertiary and secondary structures of BBP, as evidenced by the significant increase in surface hydrophobicity, more β‐turns and random coils, fewer β‐sheets, and the variation of microenvironments of certain amino acid residues. X‐ray diffractometry revealed that ACEF reduced the relative crystallinity and granular size of BBP, increased lattice spacing, caused the weakening of intermolecular forces, and significantly decreased the compactness of spatial conformations in BBP. Furthermore, the antioxidant capacity of BBP increased following ACEF treatment and was influenced by voltage. This may be due to the BBP structure unfolding and the release of aromatic amino acids.

Effect of AC electric field on enhancing phytoremediation of Cd-contaminated soils in different pH soils

To increase the efficiency of phytoremediation to clean up heavy metals in soil, assisted with alternating current (AC) electric field technology is a promising choice. Our experiments utilized the hyperaccumulator Sedum alfredii Hance and the fast-growing, high-biomass willow (Salix sp.). We investigated the efficiency of AC field combined with S. alfredii—willow intercropping for removing Cd from soils with different pH values. In the AC electric field treatment with S. alfredii—willow intercropping, the available Cd content in acidic soil increased by 50.00% compared to the control, and in alkaline soil, the increase was 100.00%. Furthermore, AC electric field promoted Cd uptake by plants in both acidic and alkaline soils, with Cd accumulation in the aboveground increased by 20.52% (P < 0.05) and 11.73%, respectively. In conclusion, the integration of AC electric fields with phytoremediation demonstrates significant favorable effectiveness.

Electrothermosolutal convection in nanofluid

This article employs linear stability theory to investigate the thermosolutal instability phenomenon within a horizontal layer of nanofluid subjected to a vertical alternating current (AC) electric field while being heated from below. The model integrates the impacts of Brownian diffusion, thermophoresis, and electrophoresis into the nanofluid dynamics. Free-free boundary conditions are assumed at the upper and lower boundaries of the fluid layer. Employing the normal mode technique, the set of coupled differential equations is solved analytically for stress-free boundaries. The computed numerical values of the stationary thermal Rayleigh number are illustrated graphically. The conditions for nonexistence of overstability are also derived. The study focuses on stationary convection, examining the analytical and graphical implications of modified diffusivity ratio, AC electric Rayleigh number, solutal Lewis number, nanofluid Lewis number, solutal Rayleigh number, and nanoparticle Rayleigh number on the system dynamics. The analysis demonstrates that the nanofluid Lewis number and modified diffusivity ratio produce a stabilizing effect on the initiation of convection, notably delaying its onset. AC electric field and solutal Rayleigh number exhibit a destabilizing influence, notably accelerating the onset of convection.

Electro-Osmotic Flow and Mass Transfer through a Rough Microchannel with a Modulated Charged Surface.

In this paper, we investigate the electro-osmotic flow (EOF) and mass transfer of a Newtonian fluid propelled by a pressure gradient and alternating current (AC) electric field in a parallel microchannel with sinusoidal roughness and modulated charged surfaces. The two-wall roughness is described by in-phase or out-of-phase sine functions with a small amplitude δ. By employing the method of perturbation expansion, the semi-analytical solutions of the Poisson-Boltzmann (P-B) equation based on the Debye-Hückel approximation and the modified Navier-Stokes (N-S) equation are obtained. The numerical solution of the concentration equation is obtained by the finite difference method. The effects of sinusoidal roughness, modulated charged surface, and the AC electric field on the potential field, velocity field, and concentration field are discussed. Under the influence of the modulated charged surface and sinusoidal roughness, vortices are generated. The velocity oscillates due to the effect of the AC electric field. The results indicate that solute diffusion becomes enhanced when the oscillation Reynolds number is below a specific critical value, and it slows down when the oscillation Reynolds number exceeds this critical value.

Tailored micromixing in chemically patterned microchannels undergoing electromagnetohydrodynamic flow.

The study unveils a simple, non-invasive method to perform micromixing with the help of spatiotemporal variation in the Lorentz force inside a microchannel decorated with chemically heterogeneous walls. Computational fluid dynamics simulations have been utilized to investigate micromixing under the coupled influence of electric and magnetic fields, namely, electromagnetohydrodynamics, to alter the direction of the Lorentz force at the specific locations by creating the reverse flow zones where the pressure gradient, . The study explores the impact of periodicity, distribution, and size of electrodes alongside the magnitude of applied field intensity, the flow rate of the fluid, and the nature of the electric field on the generation of the mixing vortices and their strength inside the microchannels. The results illustrate that the wall heterogeneities can indeed enforce the formation of localized on-demand vortices when the strength of the localized reverse flow overcomes the inertia of the mainstream flow. In such a scenario, while the vortex size and strength are found to increase with the size of the heterogeneous electrodes and field intensities, the number of vortices increases with the number of heterogeneous electrodes decorated on the channel wall. The presence of a non-zero pressure-driven inflow velocity is found to subdue the strength of the vortices to restrict the mixing facilitated by the localized variation of the Lorentz force. Interestingly, the usage of an alternating current (AC) electric field is found to provide an additional non-invasive control on the mixing vortices by enabling periodic changes in their direction of rotation. A case study in this regard discloses the possibility of rapid mixing with the usage of an AC electric field for a pair of miscible fluids inside a microchannel.

The effect of non‐contact electro capacitive cancer therapy on DMBA‐induced rat breast tumor angiogenesis

Alternating Current‐Electric Field (AC‐EF) generated by non‐contact Electro Capacitive Cancer Therapy (ECCT) can inhibit breast tumor growth. However, its effect on breast tumor angiogenesis remains unclear. Since angiogenesis is involved in normal physiology and tumors, it is crucial to investigate the effect of ECCT on normal and breast tumor angiogenesis. Samples consisting of rat breast normal tissue and breast tumors were obtained from the biobank, with tumors induced by 7,12‐dimethylbenz (α) anthracene (DMBA) at 20 mg/kg BW 10 times over five weeks. Meanwhile, ECCT exposure of 150 kHz and 18 Vpp was conducted for 21 days at 10 hours/day. The qPCR method was used for gene expression analysis, while immunohistochemistry used antibody anti‐Vegfr2 that was used to detect Vegfr2 protein expression. Data were analyzed using one‐way ANOVA and t‐tests performed with GraphPad Prism ver.9.5.1 software. The results revealed no impact of ECCT exposure on normal breast tissue angiogenesis. Interestingly, there was a significant increase in the number of blood vessels following the upregulation of Vascular Endothelial Growth Factor Receptor‐2 (Vegfr2) as opposed to its primary signal, Vascular Endothelial Growth Factor‐A (Vegfa). Furthermore, gene expression of Hypoxia Inducible Factor‐1α (Hif1α) and Specificity Protein‐1 (Sp1) was similar to that of the control group, suggesting that Vegfr2‐dependent angiogenesis regulates ECCT‐treated breast tumor angiogenesis.

Enhancement of serrawettin W1-producing Serratia marcescens cell migration by resonant oscillation under alternating current electric field

Swarming migration is observed in flagellated bacteria on wet surfaces. As the secreted biosurfactant hydrates, friction between the cell and the wet surface is reduced, and weak flagellar movement appears to be a significant force for cell translocation. Developing an artificial swarming control method could greatly aid in establishing techniques for biofilm inhibition and detachment. In this study, the effect of forced cell vibration by an alternating current electric field (ACEF) on swarming motility was investigated using the serrawettin W1-producing Serratia marcescens strain. At frequencies close to the natural frequencies of microbial cells (12 MHz), swarming motion was effectively enhanced in biosurfactant-producing S. marcescens, but not in non-surfactant-producing Escherichia coli or non-flagellated Staphylococcus aureus. Electric field-assisted cell migration was significantly induced under swarming conditions with low friction resistance between the cell and gel surface. This finding suggests a direction for developing strategies to regulate biofilm formation and detachment using ACEF-assisted oscillation of cells attached to surfaces.

Co-fired lead-free piezoceramic multilayer actuators with ultrahigh electro-strain and remarkable comprehensive properties

Piezoceramic multilayer actuators (MLAs) offer remarkable advantages across various cutting-edge applications, yet the inferior piezoelectric strain and the confined assessment framework of lead-free MLAs constitute substantial obstacles to practical implementation. Herein, we judiciously introduce defect configurations into Ag/Pd co-fired potassium-sodium-niobate-based MLAs by tape-casting technique, achieving a large converse piezoelectric coefficient of 900 pm V−1 at 20 kV cm−1 for each layer, much superior than PZT-5 H counterparts. This lead-free MLA demonstrates fast response time, high temperature stability, impressive fatigue resistance, and good mechanical property. Unlike lead-based material suffering from abundant heat generated under alternating-current electric fields, the high-activated nanosized domains and higher thermal conductivity of this lead-free ceramic collaboratively minimize heat accumulation, presenting advancements for high-frequency utilizations. Moreover, experimental demonstrations reveal that the fast-steering mirror (FSM) apparatus equipped with the lead-free MLA showcases a rotational sensitivity comparable to PZT-based apparatus, exhibiting its extensive prospect for precise positioning and fast-response applications.

Comparisons of Rice Seed Growths Due to Alternating and Direct Current Electric and Magnetic Field Influences

It is commonly known that electric and magnetic fields of power transmission negatively and positively influence plants. Unfortunately, studies on these influences are minimal, particularly considering the comparison between magnetic field and electric field, on both DC (direct current) and AC (alternating current). This research aims to compare the influences of magnetic field and electric field, both on AC and DC, on rice plant growth. Firstly, prototypes, including the equipment, were constructed to generate AC and DC electric fields using parallel plates of a medium voltage transformer and Cockroft-Walton circuits. Meanwhile, the AC and DC magnetic fields were prepared using three different diameter current-injected coils. The rice seeds were exposed to electric and magnetic fields for one month, with plate distance and coil diameter variations. The results showed that the rice seeds grew differently according to the respective types and magnitudes of the fields. In the first two days, the rice seed growths exposed to electric and magnetic fields were higher than those without field exposures. However, since the thirteenth day, the rice growth rate with field exposure was lower than without. This study also shows that the influences of the DC electric and magnetic fields were more potent than the AC fields. The averages of rice seed growth decreasing rate for the AC and DC electric fields and AC and DC magnetic fields were 0.00827 cm/(kV/m), 0.01167 cm/(kV/m), -0.13267 cm/mT and 1.99005 cm/mT, respectively. As a general suggestion in sites, rice plants should be avoided from a transmission line due to high voltage direct current (DC) rather than that alternating current (AC).

Dielectric and pseudo-dielectric heating effects in a dual-frequency liquid crystal cell

The dielectric heating (DH) effect is a common phenomenon observed in dual-frequency liquid crystal (DFLC) cells. The heating is caused by dielectric loss resulting from the hindered reorientation about the short molecular axes of the permanent dipoles under an alternating-current (AC) electrical stimulus. Recently, we have confirmed that pseudo-dielectric heating (PDH), in association with the pseudo-dielectric relaxation, occurs readily in a sandwiched LC cell with indium–tin-oxide (ITO) electrodes. This very heating effect, primarily originating from the nonnegligible resistivity of the electrode material, has long been misinterpreted as DH governed by the intrinsic dielectric property of the LC in an AC electric field. Since previous studies have suggested the presence of only DH in DFLC cells, the clarification and differentiation of PDH are highly desired. Providing compelling evidence for the independent existence of both the intrinsic DH and less-known PDH effects, this letter represents a pioneering study to demonstrate that the two heating effects exhibiting dissimilar behaviors can be unambiguously distinguished in a sandwich-type DFLC cell.

Variation of (001) surface structures of strontium titanate single crystals caused by flash event under direct/alternative current electric fields

Flash events, which are electric power spikes occurring under an electric field and temperature above the threshold, can significantly accelerate mass diffusion over short periods of time. This study investigated the surface structure of the (001) surface of strontium titanate single-crystal treated by flash events caused by direct current (DC) and alternating current (AC) electric fields from a viewpoint of surface-related mass diffusion. The surface structuring caused by flash events was significantly different among DC and AC electric fields. The DC-flash event destabilized surface steps, causing them to wander and form surface mounds with a height of several tens of nanometers. In addition, numerous two-dimensional (2D) nuclei with a size of several nanometers are formed on the terraces. In contrast, the AC-flash event stabilized surface steps without the formation of surface mounds, causing them nearly straight with uniform terrace width at approximately 500 nm. 2D nuclei with a size of a few 10 nm were formed at the step edges with round shapes. Both methods were confirmed as evidenced by the formation of two-dimensional nuclei on the surface after the flash events, to enhance surface-related mass diffusion.

Structural transition of a nanodroplet under an alternating electric field: Understandings and predictions from a dynamic density functional theory

Alternating current (AC) electric field is an efficient means in controlling the nanostructure of a material but the mechanism is not so clear in many systems. We introduced a dynamic density functional theory (DDFT) to mimic the formation and evolution of a nanodroplet/nanocluster under an AC electric field. The prediction from DDFT is qualitatively consistent with real-world experiments and molecular simulations. The influence from the AC electric field is summarized into a diagram and the transition line can be fitted into an empirical function. It seems the crystallization mechanism is different at high and low temperatures, in which the AC electric field is a favorable and unfavorable condition for crystallization, respectively. The crystallization can be divided into two steps which corresponds to the change of order parameter and free energy, respectively. Additionally, different AC waves results in similar nanostructures and the pulse wave has the highest order parameter.

Alternating Current-Electric Field Inducing Chorio Allantoic Membrane (CAM) Angiogenesis through Exogenous Growth Factor Intervention

Angiogenesis is widely used in various therapies by promoting or inhibiting the formation of new blood vessels. The use of Alternating Current-Electric Fields (AC-EF) in Electro-Capacitive Cancer Therapy (ECCT) showed its potential as an anti-cancer device, and is characterized by its anti-proliferative and pro-apoptotic effects. However, the role of AC-EF in angiogenesis remains unclear. To investigate the effects of AC-EF on CAM angiogenesis, we used the ex ovo culture method of chorioallantoic membrane (CAM). A basic fibroblast growth factor (bFGF) dose of 30 ng/µL was administered as an exogenous growth factor. The ECCT device, generating AC-EF of 150 kHz and 18 Vpp, was exposed to the CAMs. Subsequently, the 24 CAMs of chick embryo were divided into four groups. Two groups were non-bFGF-induced CAM, while the other two were bFGF-induced CAM, and each group was exposed either with or without AC-EF. The vascularization was evaluated through macroscopic observation, while vascular endothelial growth factor A (VEGFA) gene expression was measured using qPCR. The data were statistically analyzed using ANOVA with GraphPad Prism 9.5. The results showed that an AC-EF exposure had no effects on normal CAM angiogenesis (P&gt;0.05). Moreover, VEGFA gene expression did not show significant upregulation (P&gt;0.05) in the bFGF-induced CAM with or without AC-EF exposure. Interestingly, the number of new blood vessels was significantly higher (P&lt;0.05) in the bFGF-induced with AC-EF exposure than in the non-bFGF-induced group. In conclusion, AC-EF of ECCT did not affect normal angiogenesis. AC-EF may trigger CAM angiogenesis with bFGF induction. This observation suggested that AC-EF of intermediate frequency could enhance angiogenesis by administration of external growth factors, offering a potential avenue for addressing obstructive vascular conditions.

Electrical Conduction Mechanisms in Ethyl Cellulose Films under DC and AC Electric Fields.

This work reports the dielectric behavior of the biopolymer ethyl cellulose (EC) observed from transient currents experiments under the action of a direct current (DC) electric field (~107 V/m) under vacuum conditions. The viscoelastic response of the EC was evaluated using dynamic mechanical analysis (DMA), observing a mechanical relaxation related to glass transition of around ~402 K. Furthermore, we propose a mathematical framework that describes the transient current in EC using a fractional differential equation, whose solution involves the Mittag-Leffler function. The fractional order, between 0 and 1, is related to the energy dissipation rate and the molecular mobility of the polymer. Subsequently, the conduction mechanisms are considered, on the one hand, the phenomena that occur through the polymer-electrode interface and, on the other hand, those which manifest themselves in the bulk material. Finally, alternating current (AC) conductivity measurements above the glass transition temperature (~402 K) and in a frequency domain from 20 Hz to 2 MHz were carried out, observing electrical conduction described by the segmental movements of the polymeric chains. Its electrical properties also position EC as a potential candidate for electrical, electronics, and mechatronics applications.

Surface-enhanced Raman spectroscopy with single cell manipulation by microfluidic dielectrophoresis.

When exposed to an alternating current (AC) electric field, a polarized microparticle is moved by the interaction between the voltage-induced dipoles and the AC electric field under dielectrophoresis (DEP). The DEP force is widely used for manipulation of microparticles in diverse practical applications such as 3D manipulation, sorting, transfer, and separation of various particles such as living cells. In this study, we propose the integration of surface-enhanced Raman spectroscopy (SERS), an extremely sensitive and versatile technique based on the Raman scattering of molecules supported by nanostructured materials, with DEP using a microfluidic device. The microfluidic device combines microelectrodes with gold nanohole arrays to characterize the electrophysiological and biochemical properties of biological cells. The movement of particles, which varies depending on the electrical properties such as conductivity and permittivity of particles, can be manipulated by the cross-frequency change. For proof of concept, Raman spectroscopy using the DEP-SERS integration was performed for polystyrene beads and biological cells and resulted in an improved signal-to-noise ratio by determining the direction of the DEP force applied to the cells with respect to the applied AC power and collecting them on the nanohole arrays. The result illustrates the potential of the concept for simultaneously examining the electrical and biochemical properties of diverse chemical and biological microparticles in the microfluidic environment.

The influence of frequency and gravity on the orientation of active metallo-dielectric Janus particles translating under a uniform applied alternating-current electric field.

Theoretical and numerical models of active Janus particles commonly assume that the metallo-dielectric interface is parallel to the driving applied electric field. However, our experimental observations indicate that the equilibrium angle of orientation of electrokinetically driven Janus particles varies as a function of the frequency and voltage of the applied electric field. Here, we quantify the variation of the orientation with respect to the electric field and demonstrate that the equilibrium position represents the interplay between gravitational, electrostatic and electrohydrodynamic torques. The latter two categories are functions of the applied field (frequency, voltage) as well as the height of the particle above the substrate. Maximum departure from the alignment with the electric field occurs at low frequencies characteristic of induced-charge electrophoresis and at low voltages where gravity dominates the electrostatic and electrohydrodynamic torques. The departure of the interface from alignment with the electric field is shown to decrease particle mobility through comparison of freely suspended Janus particles subject only to electrical forcing and magnetized Janus particles in which magnetic torque is used to align the interface with the electric field. Consideration of the role of gravitational torque and particle-wall interactions could account for some discrepancies between theory, numerics and experiment in active matter systems.

Applying an alternating current to strontium titanate minimizes the change in oxidation state caused by flash sintering

This study estimated the amount of oxygen deficiency in SrTiO3 polycrystals that were flash sintered under direct current (DC) and alternating current (AC) electric fields, mainly by using the fine structural change of the Ti L23-edges collected by electron energy-loss spectroscopy. The DC electric field corresponded to formation of the maximum amount of oxygen deficiency at approximately δ = 0.07 as SrTiO3−δ, which corresponds to a lattice expansion of roughly 0.1% as a lattice constant of SrTiO3. Furthermore, the oxygen deficiency was distributed unevenly. The formation of dislocation networks in DC-flash-sintered SrTiO3 polycrystals might be related to the lattice strain field caused by this nonuniform oxygen deficiency. In contrast, an AC electric field did not correspond to the oxygen deficiency of SrTiO3, which is similar to the results in thermally sintered SrTiO3 polycrystals.