Alternating-current Field Research Articles

Ionic liquid-doped liquid crystal/polymer composite for multifunctional smart windows

In this work, a facile approach to fabricating multifunctional smart windows by employing an ionic liquid-doped liquid crystal (LC)/polymer composite was reported. The composite was prepared via an established method of polymerization-induced phase separation while a commercial ionic liquid was doped into the composite as a supporting electrolyte. The smart window, which was prepared by sandwiching the as-prepared composite in two indium tin oxide (ITO) glasses, can exhibit a multifunctional mode. Specifically, the light transmittance and the coloration of the windows were regulated by different external stimuli. The electrically switchable transmittance of the window was achieved by an alternating current (AC) electric field and the window transformed into a transparent state from an opaque state under the AC field. The temperature was also used to realize the heat controllable transmittance, in which the window was turbid at a lower temperature and transparent at a high temperature. The electrically induced coloration of the window was manipulated by a direct current (DC) electric field and the window was changed into a green state from a colorless state under the DC field. This work is expected to open avenues to achieve a promising candidate for multifunctional smart windows with practical applications.

Field-induced orientational switching produces vertically aligned Ti3C2Tx MXene nanosheets

Controlling the orientation of two-dimensional materials is essential to optimize or tune their functional properties. In particular, aligning MXene, a two-dimensional carbide and/or nitride material, has recently received much attention due to its high conductivity and high-density surface functional group properties that can easily vary based on its arranged directions. However, erecting 2D materials vertically can be challenging, given their thinness of few nanometres. Here, vertical alignment of Ti3C2Tx MXene sheets is achieved by applying an in-plane electric field, which is directly observed using polarised optical microscopy and scanning electron microscopy. The electric field-induced vertical alignment parallel to the applied alternating-current field is demonstrated to be reversible in the absence of a field, back to a random orientation distribution. Interdigitated electrodes with uniaxially aligned MXene nanosheets are demonstrated. These can be further modulated to achieve various patterns using diversified electrode substrates. Anisotropic electrical conductivity is also observed in the uniaxially aligned MXene nanosheet film, which is quite different from the randomly oriented ones. The proposed orientation-controlling technique demonstrates potential for many applications including sensors, membranes, polarisers, and general energy applications.

Travelling-Wave Electrophoresis, Electro-Hydrodynamics, Electro-Rotation, and Symmetry- Breaking of a Polarizable Dimer in Non-Uniform Fields.

A theoretical framework is presented for calculating the polarization, electro-rotation, travelling-wave dielectrophoresis, electro-hydrodynamics and induced-charge electroosmotic flow fields around a freely suspended conducting dimer (two touching spheres) exposed to non-uniform direct current (DC) or alternating current (AC) electric fields. The analysis is based on employing the classical (linearized) Poisson–Nernst–Planck (PNP) formulation under the standard linearized ‘weak-field’ assumption and using the tangent-sphere coordinate system. Explicit expressions are first derived for the axisymmetric AC electric potential governed by the Robin (mixed) boundary condition applied on the dimer surface depending on the resistance–capacitance circuit (RC) forcing frequency. Dimer electro-rotation due to two orthogonal (out-of-phase) uniform AC fields and the corresponding mobility problem of a polarizable dimer exposed to a travelling-wave electric excitation are also analyzed. We present an explicit solution for the non-linear induced-charge electroosmotic (ICEO) flow problem of a free polarized dimer in terms of the corresponding Stokes stream function determined by the Helmholtz–Smoluchowski velocity slip. Next, we demonstrate how the same framework can be used to obtain an exact solution for the electro-hydrodynamic (EHD) problem of a polarizable sphere lying next to a conducting planar electrode. Finally, we present a new solution for the induced-charge mobility of a Janus dimer composed of two fused spherical colloids, one perfectly conducting and one dielectrically coated. So far, most of the available electrokinetic theoretical studies involving polarizable nano/micro shapes dealt with convex configurations (e.g., spheres, spheroids, ellipsoids) and as such the newly obtained electrostatic AC solution for a dimer provides a useful extension for similar concave colloids and engineered particles.

AC Field Threshold Effect as a Key Factor toward the Efficient Heating of Fluids with NaFeO2 Magnetic Nanoparticles

AbstractPrincipal factors leading to the efficient alternating current (AC) field‐induced heating of magnetic fluids are determined based on the results of magnetic and calorimetric measurements on NaFeO2 nanoparticles and their fluids. Features of the magnetic behavior are singled out, and characteristic magnetic parameters, such as the Curie and blocking temperatures, are determined for the NaFeO2 nanoparticles. The dependence of the fluid caloric properties on the AC magnetic field amplitude and nanoparticle concentration is analyzed. It is shown that the heating efficiency of the weakly coercive NaFeO2 nanoparticles displays an amplitude threshold character, and the heating rate is critically dependent on the AC magnetic field amplitude.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Assembly of alumina particles in aqueous suspensions induced by high‐frequency AC electric field

AbstractThe role of high‐frequency alternating current (AC) electric field in the assembly of alumina particles in aqueous media was investigated. Field–particle interactions were in situ investigated for coarse and fine powder particles in very dilute suspensions. For both coarse and fine particles, AC field‐induced assembly led to the formation of chains of particles within a minute, which were aligned in the field direction. However, a much finer network of particle chains evolved in fine particle suspensions. Threshold field strength for chain formation was also lower for fine particles (28 V/mm) than for coarse particles (50 V/mm), suggesting stronger interactions for finer particles. Chain length increased with both field strength and field duration. Chain formation was attributed to mutual dielectrophoretic (DEP) interaction forces. Increase in DEP forces with field strength resulted in enhanced interactions. For finer particles, decreasing interparticle distance might have favored stronger interactions. Suspension microstructure was disrupted as soon as the field was removed. However, higher field duration was associated with an improved pattern stability and retention following the field removal. Finally, particle motion was studied in deliberately applied spatially nonuniform AC field, which revealed different mechanisms of chain formation for coarse (negative‐DEP) and fine (positive‐DEP) particles.

Analysis of Red Blood Cell Movement in Whole Blood Exposed to DC and ELF Electric Fields.

To evaluate hematological effects of direct current (DC) and alternating current (AC) extremely low frequency (ELF) electric field exposure, this study investigated red blood cell (RBC) movement in whole blood. Video images of RBCs were recorded under a microscope using specially designed electrode systems. Video analysis software was then used to measure the RBC velocity. The noise level and measurement system stability were confirmed based on results of a no‐field exposure experiment. Using the electrode system to produce a non‐homogeneous electric field, different movements were found to occur in DC and AC field exposure. The RBCs moved in the directions of the electric field and the gradient of field distribution, respectively, in the DC and AC fields. Dependences of the RBC velocity on the field strength were, respectively, linear and quadratic in the DC and AC fields. These results suggest that electrophoretic and dielectrophoretic movements were, respectively, dominant in the DC and AC fields. The magnitude of the electric field necessary to cause these effects was found to be 103–105 times greater than the internationally publicized guideline for human safety. © 2022 Bioelectromagnetics Society.

The influence of the processing parameters on the reactive flash sintering of ZrO2‐CeO2

AbstractReactive flash sintering (RFS) is a method that was recently developed to produce dense single‐phase bulk ceramic parts through solid‐state reactions in a single‐step that only takes a few minutes. The influence of the RFS parameters on the phase purity of a simple mixed oxide, (Zr0.8,Ce0.2)O2, was investigated. Parameters such as furnace temperature, furnace atmosphere, electric current density, and alternating current (AC) or direct current (DC) were examined. It was found that (Zr0.8,Ce0.2)O2 pellets with high densities, above 90% of its theoretical density, can be produced by RFS in a few minutes when RFS occurs under oxidizing atmospheres, AC fields with current densities of 100 mA·mm−2, and at a furnace temperature of 1200°C. Reducing conditions such as Ar‐H2 atmosphere and DC fields, low furnace temperatures, and low current densities resulted in phase impurities and poor reactions between the ZrO2 and the CeO2 powders. These results show that RFS is a useful method to produce mixed oxides, but it is very sensitive to the processing parameters. This is the first time that the influence of most of the RFS processing parameters has been studied systematically. Thus, the present work aims to provide guidelines on selecting the right processing parameters when exploring RFS.

Effect of alternating current field on rheology of fresh cement-based pastes

In order to further control the rheological properties of fresh cement-based pastes on demand, this paper investigated the influences of alternating current (AC) field on yield stress, plastic viscosity and thixotropic properties of fresh cement-based paste without or with mineral admixtures (including fly ash, granulated ground blast furnace slag and silica fume) by serials experiments and theoretical analysis. The results show that the yield stress greatly increased after 20min, the plastic viscosity and thixotropic area of fresh paste greatly increased after 10min with the action of applied AC field, and the rheological parameters changed more significantly with the AC voltage enlarged from 30V to 40V. Especially, the yield stress of paste increased exponentially with time under the action of AC field. The changes of the temperature of pastes were raised by the Joule heating generated by the AC field, which is the main reason for the rheology change of paste. This achievement will provide a new technical support to prevent the segregation and improve the stability of fresh concrete after casting by application of AC field.

Bone Tumor Suppression in Rabbits by Hyperthermia below the Clinical Safety Limit Using Aligned Magnetic Bone Cement.

Demonstrating highly efficient alternating current (AC) magnetic field heating of nanoparticles in physiological environments under clinically safe field parameters has remained a great challenge, hindering clinical applications of magnetic hyperthermia. In this work, exceptionally high loss power of magnetic bone cement under the clinical safety limit of AC field parameters, incorporating direct current field-aligned soft magnetic Zn0.3 Fe2.7 O4 nanoparticles with low concentration, is reported. Under an AC field of 4 kA m-1 at 430kHz, the aligned bone cement with 0.2 wt% nanoparticles achieves a temperature increase of 30 °C in 180 s. This amounts to a specific loss power value of 327 W and an intrinsic loss power of 47 nHm2 kg-1 , which is enhanced by 50-fold compared to randomly oriented samples. The high-performance magnetic bone cement allows for the demonstration of effective hyperthermia suppression of tumor growth in the bone marrow cavity of New Zealand White Rabbits subjected to rapid cooling due to blood circulation, and significant enhancement of survival rate.

AC electric field-assisted fabrication of ice-templated alumina materials and remarkable enhancement of compressive strength

A novel methodology was developed that uniquely employs alternating current (AC) electric field to fabricate ice-templated ceramics. In the methodology, AC field was applied to an aqueous ceramic suspension, and then ice-templating was performed. Field application to an aqueous ceramic suspension resulted in a net motion of ceramic particles due to DC voltage generation. Suspension concentration increased near one of the electrodes, which was controllable through AC frequency and field duration. Density of the very bottommost regions in sintered materials increased with field duration, attributed to increased local suspension concentration. In sintered materials, the thickness of non-templated region increased with field duration, whereas templated microstructure turned increasingly dendritic with field duration, suggesting a strong influence of AC field on the growth characteristics of ice crystals. AC-field assisted materials exhibited remarkably enhanced compressive strength without any change in porosity. This work contributes to advancing the ice-templating technology using externally energized fields.

Human detection thresholds of DC, AC, and hybrid electric fields: a double-blind study

BackgroundIn the course of the ongoing transition of electric energy systems, transmission corridors are often upgraded to higher voltages and other technologies leading to another quality of human exposure. The study aims to determine human detection thresholds for direct current (DC), alternating current (AC), and hybrid electric fields (various DC; constant AC).MethodsA total of 203 participants were exposed to DC, AC, and hybrid electric fields (EFs) in a highly specialized whole-body exposure laboratory using a double-blind experimental setting. Additionally, the participants were exposed to ion currents in part of the DC and hybrid sessions. To investigate environmental influences, relative humidity was changed in two subgroups during EF perception. Methods derived from the signal detection theory and the adaptive staircase procedure based on the single interval adjustment matrix were used to assess individual sensitivity and detection thresholds, respectively.ResultsThe results indicated that detection thresholds of hybrid EF were lower compared to single EF presentation of DC or AC. Ion current exposure enhanced EF perception. High relative humidity facilitated DC EF perception, whereas low relative humidity reinforced the perception of AC EFs.ConclusionsWith this systematic investigation of human perception of DC, AC, and hybrid EFs, detection thresholds were provided, which can help improve the construction processes of energy transmission systems and the prevention of unwanted sensory perception by contributing to the determination of limit values.

Convergence effect of droplet coalescence under AC and pulsed DC electric fields

The coalescence behaviors of two neutral droplets suspended in silicone oil under the alternating current (AC) and pulsed direct current (DC) electric fields are investigated by experiments and numerical simulations. The distribution evolutions of electric force and velocity field during the droplet coalescence under the AC and pulsed DC electric fields are analyzed. The relationship between electric field excitation and droplet interface response is illustrated. The equivalent response mechanism of droplets under the high-frequency AC and pulsed DC electric fields and under the DC electric fields is revealed. The relationship of droplet dynamic behaviors under the DC electric field and under the AC and pulsed DC electric fields are established. The critical electric field frequencies above which the shortest distance curves no longer change under the AC and pulsed DC electric fields are obtained. These new findings are significant for the optimization of electrostatic coalescence.

Spark Plasma Sintering of LiFePO4: AC Field Suppressing Lithium Migration.

Our work proposes a comparison between Spark Plasma Sintering of LiFePO4 carried out using an Alternating Current (AC) and Direct Current (DC). It quantifies the Li-ion migration using DC, and it validates such hypothesis using impedance spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma optical emission spectroscopy. The use of an AC field seems effective to inhibit undesired Li-ion migration and achieve high ionic conductivity as high as 4.5 × 10−3 S/cm, which exceeds by one order of magnitude samples processed under a DC field. These results anticipate the possibility of fabricating a high-performance all-solid-state Li-ion battery by preventing undesired Li loss during SPS processing.

Alignment dynamics of single-wall carbon nanotubes under electric field in different surfactant solutions

The dynamics of metallic single-wall carbon nanotube (SWCNT) alignment inside various viscous media under electric field is investigated in this simulation work for the manifestation of macroscale aligned SWCNT films. An alternating current (AC) electric field was applied to the liquid solution of several surfactants (DIW, DMF, CHEX, SDS, and DOC) containing SWCNTs. The time required for the SWCNTs to get aligned to the applied AC electric field was simulated for different initial conditions for all the surfactants. An analytical model based on dielectrophoresis induced torque was employed. The model considers the viscosity and conductivity of the surrounding medium. The influence of SWCNT length, SWCNT radius, and frequency of the AC field on the assembly of SWCNTs were studied. Our analysis showed that a longer and narrower SWCNT prompts faster assembly to an aligned SWCNT aggregation. Furthermore, the effect of the concentration of SDS and the effect of electric field strength for DIW surfactant were also investigated. Viscosity plays a significant role in the alignment process. Slower SWCNT alignment is caused by a medium of higher viscosity.

Ultra-high dynamic range quantum measurement retaining its sensitivity

Quantum sensors are highly sensitive since they capitalise on fragile quantum properties such as coherence, while enabling ultra-high spatial resolution. For sensing, the crux is to minimise the measurement uncertainty in a chosen range within a given time. However, basic quantum sensing protocols cannot simultaneously achieve both a high sensitivity and a large range. Here, we demonstrate a non-adaptive algorithm for increasing this range, in principle without limit, for alternating-current field sensing, while being able to get arbitrarily close to the best possible sensitivity. Therefore, it outperforms the standard measurement concept in both sensitivity and range. Also, we explore this algorithm thoroughly by simulation, and discuss the T−2 scaling that this algorithm approaches in the coherent regime, as opposed to the T−1/2 of the standard measurement. The same algorithm can be applied to any modulo-limited sensor.

Power dissipation in magnetic nanoparticles evaluated using the AC susceptibility of their linear and nonlinear responses

The heat dissipated by magnetic nanoparticles may be used as a heat source for hyperthermic treatment of cancer and it can be estimated based on the magnetic susceptibility when an alternating current (AC) magnetic field is applied. Here, the frequency dependence of the magnetization of magnetic nanoparticles is measured for different AC fields. This is used to examine the AC susceptibility of linear and nonlinear magnetization responses. Two methods were used to evaluate the AC susceptibility based on measured magnetization properties. The first used the static susceptibility and phase delay associated with magnetic relaxation, and the second used the area under the AC magnetization curve to derive the imaginary part of the susceptibility. When the field intensity was low, the estimated AC susceptibilities were comparable. However, when the field intensity was high, the first method predicted a lower value because it did not consider the nonlinearity of the magnetization response. To optimize the material and the applied field conditions for hyperthermia it is important to understand the difference between the two methods. The intrinsic loss power and specific loss power of the magnetic nanoparticles were also evaluated. A liquid sample and a solid sample with an oriented easy axis provided high heat dissipation.

Comparative study of AC and DC fields on wound healing

The present study was conducted with an objective to observe the wound healing capacity under the influence of alternating current (AC) and direct current (DC) fields. To fulfil the aim of the study rats and rabbits were taken as experimental animals. These animals were divided into two groups i.e. experimental and control. Equal strength of animals were taken in each of the groups. During the study period It was observed that the surface area of the DC stimulated wound healed faster in comparison to AC stimulated wound. It was also found that the volume of AC stimulated wound healed faster than DC stimulated wound. Eventually, it was observed that stimulated wound healed rapidly in experimental animals in comparison to control group.

High transparency induced by electric fields using KTN crystals

Potassium tantalate niobate, KTa1-xNbxO3 (KTN), exhibits a giant electro-optic effect with unique features. However, its relatively-low optical transmittance limits its practical applications in functional devices. Here, we report the observation of high optical transparency induced by either alternating current (AC) or direct current (DC) electric fields. The AC field induces a rapid phase transition to the paraelectric phase in KTN which has much high optical transmittance compared to its initial ferroelectric phase. On the other hand, the DC electric field causes effective alignment of all dipolar clusters to form a uniform monodomain ferroelectric state, enabling high optical transparency without any optical scattering. More importantly, the high optical transparency in this monodomain ferroelectric phase can be preserved extremely well in a certain period even after turning off the applied DC voltage. We further study the effect of KTN bandgap on the optical transmittance with and without the electric fields. It is interesting that the bandgap energy with the AC electric field is less than that with the DC electric field. Our results are important for better understanding the phase-transition mechanism under electric fields. Also, high optical transparency is much desired for device applications with improved performances.

AC/DC Fields Demodulation Methods of Resonant Electric Field Microsensor.

Electric field microsensors have the advantages of a small size, a low power consumption, of avoiding wear, and of measuring both direct-current (DC) and alternating-current (AC) fields, which are especially suited to applications in power systems. However, previous reports were chiefly concerned with proposing new structures or improving the resolution, and there are no systematic studies on the signal characteristics of the microsensor output and the demodulation methods under different electric fields. In this paper, the use of an improved resonant microsensor with coplanar electrodes, and the signal characteristics under a DC field, power frequency field, and AC/DC hybrid fields were thoroughly analyzed respectively, and matching demodulation methods derived from synchronous detection were proposed. We theoretically obtained that the frequencies of the detectable electric fields should be less than half of the resonant frequency of the microsensor, and that the sensitivities of the microsensor were identical for AC/DC hybrid fields with different frequencies. Experiments were conducted to verify the proposed demodulation methods. Within electric field ranges of 0–667 kV/m, the uncertainties were 2.4% and 1.5% for the most common DC and 50 Hz power frequency fields, respectively. The frequency characteristic test results of the microsensor were in agreement with those of the theoretical analysis in the range of 0–1 kHz.