Influence Of AC Electric Field Research Articles

High-field complex parameters characterization of PMN-PT single crystal/epoxy 1–3 composites (φ = 0.4) under a high AC electric field with a varied intensity

It is essential to characterize the high-field properties of piezoelectric composites for their applications in ultrasonic transducers. This study involved the development of an experimental characterization system of piezoelectric impedance spectra and mechanical quality factors under high-field conditions to analyze the properties of PMN-PT piezoelectric single-crystal composites. The impedance spectra and mechanical quality factors of a [001]c-poled 0.69PMN-0.31PT single crystal/epoxy 1–3 composite disk with filling ratio φ = 0.4 under thickness resonance mode were tested at different driving voltages ranging from 1 to 120 Vpp to explore the influence of AC electric field on the material properties. By utilizing a theoretical approach, an evaluation was conducted on the variations in the material properties such as stiffness, permittivity, piezoelectric coefficient, and electromechanical coupling factor, along with respective loss factors. Our results suggest that as the AC electric field increases, the elastic modulus c33D and the mechanical quality factor Qm decrease, while the piezoelectric strain coefficient d33 and the electromechanical coupling factor kt increase. However, the dielectric coefficient ε33X does not show an obvious change in this field range. Furthermore, the elastic loss factor tanϕ, the dielectric loss factor tanδ33′, the piezoelectric loss factor tanθ33′, and the electromechanical coupling loss factor tanχt all increase, indicating that the loss of the piezoelectric composite becomes more evident as the AC electric field grows.

Numerical investigation of electroosmotic mixing in a contraction–expansion microchannel

Electroosmotic micromixing is generally a highly desirable technique in microanalysis systems due to its ability to mix fluids at the microliter level. Herein, a contraction-expansion microchannel is used to conduct a numerical study on the mixing caused by AC electroosmotic. We investigate the flow and concentration field distributions in the microchannel and observe two circulation flows and four rotating vortices generated in the expansion chamber by the influence of AC electric fields. The generation of the rotating vortex is highly dependent on the relative magnitudes of the electroosmotic force and inertia force. Higher inertial force prevents vortex formation and significantly reduces the mixing quality under higher inlet velocity. We also explore the influence of inlet velocity, frequency, and voltage on the vortex formation and mixing performance. The best mixing quality (0.997) is obtained at the inlet velocity of 0.2 mm/s with 0.1 V voltage in a 70 μm length-channel and the pressure drop is only 1.58 Pa. The current micromixer provides a favorable method of mixing fluid based on electroosmotic and could improve the mixing quality in microfluidic analysis devices.

Entropy of AC electro-kinetics for blood mediated gold or copper nanoparticles as a drug agent for thermotherapy of oncology

Nanoparticles play a radical role in oncology treatment especially nanoparticles of gold (Au NPs). Among the substantial properties of Au NPs is the possession of a large atomic number, which helps in the treatment of tumors. Furthermore, it is employed to encapsulate large numbers of therapeutic compounds. Also, the alternating electric field therapy (AC electro-kinetics, called tumor treating fields TTF), is used in malignancy oncology therapy (MOT). The aim of this article is to investigate the blood flow characteristics under the influence of AC electric field and heat transfer in the presence of Au and Cu-NPs through a symmetric elastic sinusoidal channel. The governing equations of the Jeffrey fluid (blood model) along with total mass, thermal energy, and the electric potential equations are simplified by using the postulate of long wavelength approximation. The expressions of the axial velocity field, stream function, pressure gradient, the temperature distribution, and the electric potential field are obtained by using DSolve program in Mathematica software (version 10). Influence of the materialistic parameters like the Jeffrey parameter, volume fraction, Grashof number, and electric Rayleigh number on the velocity profile, temperature distribution, electrical potential, pressure gradient, pressure rise, and entropy generation are considered. Two different nanofluid suspensions are investigated (Au and Cu NPs). The results pointed out that the Au-NPs are efficacious for drug carrying and drug delivery systems, this is evidenced by the velocity in the case of Au-NPs greater than in the case of Cu-NPs. Also, when the electrical Raleigh number increases, an electric force is generated to reverse the wave propagation.

Linear aggregation of spherical nanogolds in carbon nanotube suspension under influence of AC electric field

We reported a novel method to align spherical nanogolds into linear chains, mediated by induced-electric dipoles from carbon nanotubes in the suspension under AC field. Nanogolds were suspended along with carbon nanotube in water under an AC field of magnitude 100 volts/mm and frequency range of 25 - 1, 000 KHz. Typically the electric polarization of nanoparitcles are very small because of their small volume and we did not observe their dipole-dipole interaction forces under the presence of electric field. However, introducing carbon nanotubes into the suspension made the nanogolds interact with each other and form linear chains directed along the field line. We also found that linear chains can attract from the side and form fatter chains.

Influence of AC electric field on the charge generation in albumin solution in a flow-based AFM fishing system

In the present paper, the influence of AC electric field on charge accumulation in the measuring cell of a flow-based system for atomic force microscope (AFM) based fishing is considered. As a flow-based system, a device for AFM-based fishing of low-abundant proteins has been employed. The charge is generated in a femtomolar albumin solution during its flowing through an injector of this system. We have demonstrated that application of sinusoidal electric field (100 V, 50 Hz frequency) stimulates charge accumulation in the measuring cell upon the input of protein solution at 38°C. Taking this effect into account is of importance for the development of novel highly sensitive flow-based proteomic and diagnostic systems employing AFM-based fishing, for modeling the influence of electric field on hemodynamics, and also for the development of specified theoretical models describing physicochemical properties of water and aqueous solutions.

Discharge Characteristics of Short Air Gap and Insulation Surface Under Flame Conditions

An experimental study was conducted to investigate the discharge characteristics of short air gap and insulation surface under flame conditions. The influence of ac electric field on flame and the mechanism leading to the reduction of breakdown voltage under flame conditions are analyzed. Results show that under the ac electric field, the flame is deflected to the high voltage electrode, and compared with normal conditions (without flame), the breakdown voltage of the short air gap and the insulation surface is decreased by 74.4% and 70%, respectively. Besides, arc levitation appears at high probability under the flame conditions. Furthermore, the decrease of the breakdown voltage of short air gap and the flashover voltage of insulation surface under the flame conditions are mainly due to the increase of the air conductivity and the decrease of the air density. For the insulating dielectric, the change of the flashover path is also one of the main reasons for the decrease of the flashover voltage.

Electrostatic suppression of the Leidenfrost state using AC electric fields

The formation of a vapor layer at the solid-liquid interface at high temperatures (Leidenfrost phenomenon) degrades heat transfer substantially. Application of an electric field in this vapor layer can fundamentally eliminate the Leidenfrost state by electrostatically attracting liquid towards the surface. This study analyzes the influence of AC electric fields on electrostatic suppression of the Leidenfrost state; previous studies have only utilized DC electric fields. In particular, the influence of the frequency of the AC waveform on Leidenfrost state suppression is analyzed using high speed visualization of liquid-vapor instabilities and heat transfer measurements of evaporating droplets. It is seen that the extent of suppression is reduced with increasing AC frequency. At sufficiently high frequencies, the influence of an applied voltage is completely negated, and electrostatic suppression of the Leidenfrost state can be completely eliminated. A first-order electromechanical model is used to explain the frequency-dependent reduction in the electrostatic attraction force on the Leidenfrost droplet. Overall, this work highlights the importance of AC frequency as a tool to control the extent of suppression and the boiling heat transfer rate.

Novel effect of spin dynamics with suppression of charge and orbital ordering in Nd0.5Ca0.5MnO3 under the influence of ac electric field

Dynamics of spin ordering in the manganite Nd0.5Ca0.5MnO3 have been investigated in this paper. It was observed that the complex mixed magnetic ordering in pellets is comprised of antiferromagnetic ordering at 160K (TN) and complete charge ordering at 250K (TCO). Under ac field, appearance of unstable ferromagnetic correlations is observed above TCO, which is badly frustrated due to strong spin disorder induced by Jahn Teller distortions. Impedance measurements reveal the spin glass like scenario, suppressing the strong antiferromagnetic and charge ordering states below TN.

AC electric field controlled non-Newtonian filament thinning and droplet formation on the microscale.

Monodispersity and fast generation are innate advantages of microfluidic droplets. Other than the normally adopted simple Newtonian fluids such as a water/oil emulsion system, fluids with complex rheology, namely, non-Newtonian fluids, which are being widely adopted in industries and bioengineering, have gained increasing research interest on the microscale. However, challenges occur in controlling the dynamic behavior due to their complex properties. In this sense, the AC electric field with merits of fast response and easiness in fulfilling "Lab on a chip" has attracted our attention. We design and fabricate flow-focusing microchannels with non-contact types of electrodes for the investigation. We firstly compare the formation of a non-Newtonian droplet with that of a Newtonian one under an AC electric field and discover that viscoelasticity contributes to the discrepancies significantly. Then we explore the effect of AC electric fields on the filament thinning and droplet formation dynamics of one non-Newtonian fluid which has a similar rheological behavior to bio samples, such as DNA or blood samples. We investigate the dynamics of the thinning process of the non-Newtonian filament under the influence of an AC electric field and implement a systematic exploration of the non-Newtonian droplet generation influenced by parameters such as the flow conditions (flow rate Q, capillary number Ca), fluid property (Weissenberg number Wi), applied voltage (U) and frequency (f) of the AC electric field. We present the dependencies of the flow condition and electric field on the non-Newtonian droplet formation dynamics, and conclude with an operating diagram, taking into consideration all the above-mentioned parameters. Results show that the electric field plays a critical role in controlling the thinning process of the filament and the size of the generated droplet. Furthermore, for the first time, we quantitatively measure the flow field of the non-Newtonian droplet formation under the influence of an AC electric field, assisted by a high-speed micro particle imaging velocimetry (μPIV) system. The flow field distributions obtained using the correlation algorithm show that the electric field generated Maxwell stress deforms the interface, changes the flow recirculation pattern, stimulates the instability and hence reduces the size of the non-Newtonian droplet. Finally, we analyze the impact of Maxwell stress by means of the electric capillary number CaE. Our findings reveal the rich physics of non-Newtonian fluids and widen the applications of electric field in non-Newtonian environments, which could be critical for bioengineering.

Influence of AC electric field on conductor icing

Atmospheric icing of conductors is a major issue for the safety, design and operation of transmission lines. In the presence of an electric field on the surface of the conductor, ice accretion mechanism behaves differently compared to non-energized state. To investigate the influence of AC electric field on conductor icing, laboratory experiments were carried out in a cold climate room. The experiments dealt with hard rime and glaze ice because these two types of ice are among the most dangerous ones to a power system. The experimental results showed that the AC electric field has a significant influence on the ice weight, icicle spacing, length, and the deviation angle. Based on the experimental results, the influence of AC electric field on ice accretion of energized conductors was then analyzed and discussed.

Effect of interaction between AC electric field and phonon oscillation of metal cluster on tip-growth of carbon nanotube

The paper reports effect of interaction between AC electric field and metal cluster sitting at tip end of the carbon nanotube (CNT) on CNT tip-growth in CVD theoretically. For this purpose, a theoretical model based on phonon oscillations of the metal catalyst and influence of AC electric field on these oscillations is presented. Results show that there is an optimum AC electric field which optimizes growth of ultra-long CNTs. Then it is demonstrated that, in comparison with CNTs in the absence of field, CNTs under optimum electric field grow more. In addition, relation between optimum temperature and amplitude of AC electric field is investigated and it is shown that increasing electric field leads to higher optimum temperature. Finally, Investigation of effect of catalyst type on optimum electric field demonstrates the optimum field for various catalysts is different due to their different characteristics including van der Waals interaction with carbon, atomic mass and number of free charge carriers per each atom. All results are discussed and interpreted.

AC Electrophoresis; Deposition of Ceramic Nanaoparticles on In-plane Electrodes at Low Frequencies (RESEARCH NOTE)

Deposition of ceramic nanoparticles (dispersed in a non-aqueous suspension) on in-plane electrodes and under the influence of AC electric fields in the frequency range of 0.01 Hz - 10 kHz is investigated. Analysis of the particle response to the applied field is a difficult task due to the mutual effect of electric- and hydrodynamic force which are present in the system. In this work, however, we show the possibility of dividing the frequency range into four domains with four distinct governing mechanisms. Possible mechanisms are suggested and dominant forces are determined for each domain. In situ optical microscopy observations as well as numerical calculations are used for three dimensional visualization of nanoparticles´ movement dispersed in liquid medium. New applications such as micro-patterning and sorting ceramic particles are introduced for the first time.

The mechanisms of heat transfer during convective boiling under the influence of AC electric fields

In this investigation the local heat transfer coefficients along the top and bottom of a horizontal tube heat exchanger within which convective boiling of HFE7000 is occurring are measured. Of particular focus is the influence of Electrohydrodynamics (EHD) on the flow regimes and associated heat transfer. To achieve this, thermocouples are embedded into the walls of a transparent sapphire tube coated with a transparent yet electrically conductive layer of Indium Tin Oxide (ITO). The ITO layer allows visual access to the two phase flow while at the same time acts as an electrical heater element for the heat transfer and electrical ground for establishing the electric field. Tests have been performed for a fixed mass flux of G=100kg/m2s, inlet quality of x=3% and applied heat flux of q″=12.4kW/m2. An AC 60Hz high voltage was applied across the fluid up to 8kV in increments of 1kV. The results show that, for the conditions tested, the application of EHD substantially increases the heat transfer coefficient at all measurement locations on the heat exchanger. Near the entrance, the top surface heat transfer enhancement reached over 7.2-fold and this decreased monotonically to 2.4-fold at the exit region. The bottom enhancement was more uniform along the heat exchanger ranging between approximately 3 and 4-fold at the highest applied voltage tested. The mechanisms responsible for the observed enhancement levels are discussed in the context of the flow regimes observed using high speed videography.

AC Electrophoresis, a New Technique for Deposition of Ceramic Nanoparticles; Introduction, Application and Mechanism

Deposition of ceramic nanoparticles (dispersed in non-aqueous suspension) on in-plane electrodes and under the influence of AC electric fields in the frequency range of 0.01 Hz - 10 kHz is investigated. Analysis of the particle response to the applied field is a difficult task due to the mutual effect of electric and hydrodynamic forces which are present in the system. In this work, however, we show the possibility of dividing the frequency range into four domains with four distinct governing mechanisms. Possible mechanisms are suggested and dominant forces are determined for each domain. In situ optical microscopy observations are used for visualization of nanoparticles´ movement dispersed in liquid medium. These observations show that applying AC electrophoresis at frequencies below 10 kHz is an effective way for manipulating ceramic nanoparticles and device fabrication.

Influence of AC Electric Field on Macroscopic Network of Carbon Nanotubes in Polystyrene

CVD‐grown multiwall carbon nanotubes are dispersed in styrene monomer. During the polymerization of styrene, an AC electric field is applied to induce the CNTs to align along the electric field line to form a macroscopic nanotube network in polystyrene matrix. The dielectrophoresis force and the electric field redistribution at the CNTs apexes are responsible for alignment of the CNTs as well as bonding between the CNTs. Parameters such as field strength and nanotube weight fraction are varied. The results indicate that the macroscopic CNTs alignment along electric field direction can be observed only if the AC voltage reaches or is higher than certain values, and the higher the electric field frequency is, the more uniformly the CNTs align along electric field direction. In addition, nanotube concentration also affects the alignment of CNTs. According to the results of this study, the CNTs will align into a developed network in polystyrene matrix under a proper combination of three parameters of the electric field voltage, frequency, and the CNTs concentration.

The influence of ac electric field on the domain growth and alignment of the ferroelectric liquid crystal cell with N*–SmC* phase transition

The mechanisms of domain growth and the formation of alignment of the ferroelectric liquid crystal (FLC) were investigated under an applied alternating current (ac) electric field during N*–SmC* phase transition. Varying the frequency of the ac electric field allowed for the domain size and average dynamic molecular axis of a FLC cell to be controlled. In addition, the mechanism of alignment in the FLC cell with an ac electric field, which is applied to the FLC cell during N*–SmC* phase transition, was clarified.

Influence of AC Electric Field on Dispersion of Carbon Nanotubes in Liquids

Production processes for carbon nanotubes commonly produce mixtures of solid morphologies that are mechanically entangled or that self‐associate into aggregates. The entangled or aggregated carbon nanotubes often need to be dispersed in liquids for further applications. The authors propose an innovative dispersion method for carbon nanotubes by which an AC electric field is applied to suspensions of carbon nanotubes. The dispersion status of carbon nanotubes in liquid media is evidently improved by an AC electric field and is strongly dependent on the magnitude, the frequency, and the exerting time of the applied electric field. Fine carbon nanotube dispersion is achieved with an AC electric field of high voltage, low frequency, and proper exerting time. A certain relation between the dispersion status and the current between the metal electrodes through the carbon nanotube suspension is also observed. The dispersion of carbon nanotubes is ascribed to the AC electric field induced simple harmonic motions with different amplitudes of different carbon nanotubes.

Effect of electric fields on reattachment and propagation speed of tribrachial flames in laminar coflow jets

The effects of electric fields on the reattachment of lifted flames have been investigated experimentally in laminar coflow jets with propane fuel by applying high voltages to the fuel nozzle. In case of AC, the frequency has also been varied. Results showed that reattachment occurred at higher jet velocity when applying the AC voltages, thus the stabilization limit of attached flames was extended by the AC electric field. Higher voltage and lower frequency of the AC were found to be more effective. On the contrary, the effect of DC was found to be minimal. To understand the early onset of the reattachment with the AC, occurring at higher jet velocity, the influence of AC electric fields on the propagation speed of tribrachial flame edge was investigated during the transient reattachment processes. The propagation speed increased reasonably linearly with the applied AC voltage and decreased inversely to the distance between the flame edge and the nozzle electrode. Consequently, the enhancement in the propagation speed of tribrachial flame edge was correlated well with the electric field intensity, defined as the applied AC voltage divided by the distance.

Numerical solution of the dielectrophoretic and travelling wave forces for interdigitated electrode arrays using the finite element method

AC electrokinetics is the study of the movement of polarisable particles under the influence of AC electric fields. The fields are applied to a suspension of particles by planar microelectrode structures and one particular design, the interdigitated bar electrode has been used in both dielectrophoretic (DEP) field flow fractionation and travelling wave dielectrophoresis. This paper presents, numerical solutions of the DEP and travelling wave forces for an interdigitated electrode array energised with either a 2- or 4-phase signal. The electrorotational torque experienced by the particle in the 4-phase travelling wave array is also calculated. The solutions are compared with previous results.

Pitting mechanism on lubricated surface of babbitt alloy/bearing steel pair under ac electric field

The mechanism of electrical pitting on the lubricated surface of babbitt alloy/steel pair is investigated, and the threshold condition to avoid the occurrence of electrical pitting is also established by using a static electrical pitting tester with high precision under the influence of ac electric field. According to the SEM micro-graph and EDS analysis are, the mechanism of electrical pitting is significantly influenced by the interface power and the oil film thickness. At the smaller oil film thickness, the eroded surface of babbitt alloy exhibits a concave crater with a few micro-porosity in the vicinity of center region with a plateau on its surrounding, especially at high supply current. The polished track can be observed at the plateau. A large amount of tin element transfers to the steel ball surface because the molten tin contacts the ball. At the higher oil film thickness, only a little amount of metal element transfers to each other. The major pitting area of the babbitt alloy is caused at the initial stage of the arc discharge. With increasing arc discharge time, the pitting area increases slowly, and finally reaches a saturated value. When the electrical pitting occurs, correlation formula for the electrical pitting area in terms of interface power and melting point of material has been established. It is found that the higher interface power and the lower melting point of material, the higher electrical pitting area. Two electrical pitting regimes are found, namely, pitting and no-pitting regimes. The boundary between the pitting and no-pitting regimes is called the threshold voltage. Correlation formula for the threshold voltage in terms of oil film thickness and melting point of material is derived.