Square-wave Electric Field Research Articles

High thermal conductivity composite h-BN/EP obtained by pulsed square-wave electric field induction

Electric fields are effective in inducing the orientation of highly thermally conductive fillers in polymers to improve the thermal conductivity of composites. However, the study of the effect of pulsed square wave electric field on thermal conductivity of composites is relatively rare. In this paper, the effect of electric field strength, frequency, and application time of pulsed square-wave electric field on the thermal conductivity of composites is investigated by utilizing the pulsed square-wave electric field to induce the orientation arrangement of h-BN in epoxy resin (EP). The results show that the thermal conductivity of the composites increases with the increase of the electric field strength and the decrease of the frequency, and does not change significantly with the application time. The highest thermal conductivity of 0.453 W/(m·K), which is 3.24 times higher than that of the epoxy resin, was obtained for the composites by applying a pulsed square-wave electric field of 200 V/mm at 0.001 Hz for 1 h with 10 wt% load. It is 1.94 times higher than that of the sample without electric field induction at the same load. This paper also establishes a mathematical relationship between the degree of orientation of h-BN and the thermal conductivity of the composite material, which expands the scope of application of the thermal conductivity model and increases the accuracy of the model calculation. The method is simple in process and suitable for a wide range of high thermal conductivity composite applications with great potential for development.

Tunable Memory and Activity of Quincke Particles in Micellar Fluid

Memory can remarkably modify the collective behavior of active particles. We show that, in a micellar fluid, Quincke particles driven by a square-wave electric field exhibit a frequency-dependent memory. Upon increasing the frequency, a memory of directions emerges, whereas the activity of particles decreases. As the activity is dominated by interaction, Quincke particles aggregate and form dense clusters, in which the memory of the direction is further enhanced due to the stronger electric interactions. The density-dependent memory and activity result in dynamic heterogeneity in flocking and offer a new opportunity for research of collective motions.

Simultaneous enhancement of the electrocaloric effect and electrostrain via exploiting the reversible polarization rotation

Self-actuating ferroelectric cooling technology have drawn increasing attention for its extensive application prospect, where simultaneous enhancement of electrocaloric effects (ECE) and electrostrain (ES) in ferroelectric materials is necessary prerequisites for the efficient operation of the cooling system. In this work, we proposed a self-actuating dual cooling cycle system combining the positive and negative ECE/ES effect, and further confirmed its feasibility in 0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-30PT) single crystal via bipolar electric field regulation. A suitable reverse electric field can generate negative ECE and ES simultaneously due to the reversible polarization rotation, whereas a high reverse electric field will lead to a serious perform loss as a result of emergent irreversible polarization jumping. The optimal reverse electric field (-Eop) can enhance the total ECE and ES by 31% and 17% respectively, whose effective combination can significantly improve the cooling capacity of the self-actuating cooling system. Moreover, compared to traditional P-E and/or I-E measurements, we proposed a more applicable and precise method to determine the -Eop under square-wave DC electric field, i.e. capacitance-voltage measurement. Our work not only provides new ideas for improving the ECE and ES of the ferroelectric materials, but also promotes the design of ferroelectric cooling systems.

Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure and macroscopic polarization

The twist-bend nematic (Ntb) phase is a recent addition to the family of nematic (N) phases of liquid crystals (LCs). A net polar order in the Ntb phase under an external electric field is interesting and it was predicted in several recent theoretical studies. We investigated the field-induced polarization behaviour, dielectric, and electro-optic properties of a bent LC dimer CB7CB in the N and Ntb phases. A threshold-dependent polarization current response was obtained in both the phases under triangular and square-wave input electric fields, existing till frequencies as high as 150 Hz. The polarization switching times were found in ∼1 ms region, especially in the N phase. In the Ntb phase, electric field-induced deformation of the helical structure was observed, like ferroelectric LCs. Dielectric measurements revealed the presence of cybotactic clusters via collective relaxations. The dielectric anisotropy (Δϵ) is negative at the frequencies of polarization measurements. The net polarization resulted from field-induced reorientation of cybotactic clusters and additionally from the field-induced deformation of helical structures in the Ntb phase. We explored the possibility of ionic contributions to the net polarization by synthesizing TiO2 nanoparticles (NPs) dispersed CB7CB LC nanocomposite. Incorporation of the NPs resulted in reduction of the collective order, increase in the ionic impurity content and conductivity, but an extinction of the field-induced polarization response. Our results demonstrate that the net polarization has competing contributions from both ferroelectric-like and ionic origin (up to ∼10 Hz) in the LC phases, but it becomes dominantly ferroelectric-like at higher frequencies.

Influence of voltage amplitude parameters on the electrocaloric response in ferroelectric materials

Direct electrocaloric effect of BaTiO3-based ceramic materials was measured during poling and partial reverse poling using a square-wave electric field. A strong influence of the amplitude of the reverse bias field on the electrocaloric response was found. With increasing amplitude of the reverse bias field, the electrocaloric response was suppressed depending on the coercive field of the material and nature of the ferroelectric-to-paraelectric phase transition.

Simulation Study of In-Phase and Out-Phase Enhanced Absorption of Graphene Based on Parity–Time Symmetry One-Dimensional Photonic Crystal Structure

In the field of modern optical communication systems and photoelectric detection, new components with complex functions and excellent performance are urgently needed. In this paper, a graphene-based parity–time (PT) symmetry structure is proposed, which is achieved by preparing the graphene layer on the top of a PT-symmetry photonic crystal. The transfer matrix method was used to calculate the absorptance of graphene, and a unique amplified absorption effect was found. Meanwhile, the peak value and wavelength position of the absorption can be modulated via the applied electric field. The results show that by adjusting the negative square-wave electric field from −3.5 × 10−5 to −13.5 × 10−5 V/nm (or the positive square-wave electric field from 2 × 10−5 to 11 × 10−5 V/nm), the proposed structure can achieve in-phase (or out-phase) enhanced absorption for the communication wavelength 1550 nm, with the absorption of graphene from 17 to 28 dB (or 30 to 15 dB) corresponding to the square-wave modulation electric field change. The modulable absorption properties of graphene in the structure have potential in optoelectronic devices and optical communication systems.

Actuation Properties of Paper Actuators Fabricated Using PEDOT/PSS Electrode Films.

The development of actuators for power sources is essential for the efficient manipulation of fluids in microfluidics systems. In this work, a capacitor-type three-layer paper actuator was fabricated by sandwiching a polyelectrolyte layer between two films of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS). The paper actuator exhibited stable large electromechanical deformations in bilateral symmetry under alternating square-wave electric field. The actuation properties were examined in a function of voltage (±0.5, ±1, ±1.5, ±2, and ±2.5 V) and frequency (1, 0.5, 0.2, and 0.05 Hz). In addition, the PEDOT/PSS electrode films with different thicknesses were prepared, and the effects of actuator thickness on actuation properties were examined. As a result, it was found that the actuator displacement increased considerably with reducing actuator thickness. In addition, the actuator with a thickness of 48 μm demonstrated a maximum displacement of 5.8 mm at a voltage of 1.5 V and a frequency of 0.05 Hz. The proposed actuator can be potentially used in the development of power sources for micropumps and check valves of microfluidic devices.

Alignment and counting of mitochondria based on capillary electrophoresis

The mitochondria are referred to as the ‘power houses’ of the cell. The number of mitochondria is considered to be related to various diseases (e.g., obesity, degenerative diseases, and aging), and thus counting the number of mitochondria in per cell is helpful for the elucidation of the rare cells. Here, we report a mitochondria-aligning system that can realize mitochondrion counting based on capillary electrophoresis technology. By electrophoresis of fluorescent microsphere in a capillary with internal diameter approximated to the size of mitochondrion (0.5–1.5 μm), we find that the microsphere aggregated under DC voltage mode, corresponding to the peak intensity appeared much larger than that of one microsphere. After applying square-wave pulsed electric field, the fluorescence signal from one microsphere immediately appeared, indicating that the microsphere aligned one-dimensionally and migrated through a narrow capillary. Based on the above phenomenon, we evaluated the mitochondria in per cell of COS-1, NIH3T3, brown fat precursor cell, and brown fat cell, respectively.

Monosex-Male Sex Reversal of Nile Tilapia Eggs Using Pulse-Electric Field Inductions

This work proposes an alternative technique of monosex-male reversal for Nile tilapia (O.niloticus) using transient pulse-electric fields to minimize time consumption of the sex reversal treatment and androgen hormone dose instead of 28-days conventional feed-fry treated and immersion techniques which uses very large amounts of 17-methyltestosterone (MT) hormone. Electrical model of nonspherical fish’s egg was developed to evaluate the induced transmembrane potential using an RCmodel to correct the ambiguities about the shell thickness and the estimated dielectric properties of the egg membrane for inductions. The parallel-plate electrode equipped with a sequential signal pulse-generator (SPG) (to be patented) has been developed. The eggs of O.niloticus (2‐3 days postfertilization) were carefully induced in square-wave electric fields of 0.25‐87.50 kV ·m −1 .W e experimentally optimized induction of O.niloticus’s egg by adjusting the number of 1‐5 square wave pulses and 5‐10 s pulse durations. The suspending medium of electroporation (EPM) was prepared by mixing HEPES buffer with the minimized concentration of MT. Verifications of sex reversal of the induced eggs have been carried out with autopsies of 2 months old of sex-reversed fry by using the aceto-carmine stain technique. The optimized conditions were 3 square wave pulses of 87.50 kV ·m −1 electric fields but a 89.25% sex reversal of eggs was achieved with less than 25% egg death. The prototype of the electrode equipped with the controlled SPG for on-site inductions could operate with 50 eggs of O.niloticus for each induction with the rapid time consumption.

Charged dendrimers under the action of AC electric fields: breathing characteristics of molecular size, polarizations, and ion distributions.

Langevin dynamics simulations are performed to study the response of charged dendrimers in alternating current electric fields in 3:1 salt solutions. Time evolutions of molecular size show breathing characteristics which take saw-tooth-like patterns in square-wave electric fields and undulated sine-function ones in sine-wave fields. Detailed study reveals how the dendrimer and condensed ions oscillate in the electric fields, which result in polarization of the molecule. To effect a significant deformation of the dendrimer, the applied field amplitude must be larger than some critical strength Ecrit and the field frequency smaller than a threshold fcrit. The response behavior is characterized by two relaxation times in square-wave fields, both of which decrease linearly with the strong field strength larger than Ecrit. In sine-wave fields, the molecular size exhibits interesting hysteretic behavior in plotting the curves with the field variation. A Maxwell-Wagner type polarization theory is derived and proved by simulations, which connects fcrit with the strength of the applied electric field.

Dipolar response and hydrogen-bond kinetics in liquid water in square-wave time-varying electric fields

Non-equilibrium molecular dynamics simulations of liquid water have been performed at 298 K in the presence of external time-varying electric fields, approximating a square wave, of varying peak intensity (0.005–0.1 V/Å) in the microwave to far-infrared frequency range (20–500 GHz). Significant non-thermal field effects were noted in terms of dipolar response and acceleration of hydrogen-bond kinetics. The coupling between the total dipole moment and the external field has been investigated and autocorrelation functions (ACFs) of both the total dipole moment and the average of the individual molecular dipole moment along the laboratory axis of the applied fields exhibited coupling, with the former showing a stronger coupling and the latter showing coupling to lower magnitude fields. The maximum alignment achieved has been computed as a function of field intensities and frequencies: the lower frequencies show a greater maximum alignment as the system had more time within each field cycle to respond. The normalised probability distribution and the hydrogen-bond ACFs have been computed: the ACF showed a clear effect over shortening the hydrogen-bond relaxation time. The field effects over the molecules’ transitions from four to five hydrogen bonds have been computed. There was an enhancement of fewer molecules undergoing transitions and a dampening for a larger proportion of molecules, depending on the external fields’ periods.

Translational and rotational diffusive motion in liquid water in square-wave time-varying electric fields

Non-equilibrium molecular dynamics (NEMD) simulations of liquid water have been performed at 298K in external square-wave electric fields. Significant non-thermal field effects were noted for coupling of rotational and translational motion with marked increases in diffusion. Non-linear field effects were evident above around 0.05VÅ−1, with enhancements in translational and rotational motion. Translational and librational modes orthogonal to the field’s direction were promoted in higher- and lower-frequency fields, respectively, owing to respective coupling of field periods with dipolar and hydrogen bonding relaxation timescales and promotion of libration about a more ‘stationary’ dipolar alignment for more sustained periods.

Water film washers and mixers: their rotational modes and electro-hydrodynamical flows induced by square-wave electric fields

Our study indicates suspended water films, driven by crossed square-wave electric fields, may act as “washers”, “centrifuges” and “mixers”. Based on our recent model successfully describing experimentally observed electro-hydrodynamical flows in water films, we derive conditions for generating specific rotational flows. Our main findings, which are advantageous for microfluidic devices and basic research, are as follows: (1) the film’s rotational patterns depend on the phase difference $$\Updelta\varphi$$ and frequencies f of the applied fields. (2) For $$\Updelta\varphi=\pi/2$$ and $$f\sim10^{-1}-10^{0}$$ Hz, the film exhibits symmetrical reciprocating rotations, i.e. it constitutes a washer. (3) For $$\Updelta\varphi=0$$ and any f, it exhibits an ordinary anticlockwise (or clockwise) rotation, i.e. it constitutes a centrifuge or motor. (4) For $$\Updelta\varphi$$ with other values and f below 1 Hz, it exhibits asymmetrical reciprocating rotations, it constitutes an asymmetrical mixer.

Optimization of a diverging micromixer driven by periodic electroosmotics

In this study, we investigate the mixing performance of a diverging microchannel driven by periodic electroosmotics. Applying two square-wave electric fields to the two inlets, the influences of the half-angle of the diverging section and the phase difference of the two actuating voltages are explored using different voltage configurations and superimposed pressure heads. Based on the analysis and flow visualization results, we find that two mixing mechanisms are present in the diverging micromixer driven by periodic electroosmotics: flow instability and fluid lamination. Furthermore, both the alternation of electric field and conductivity gradient present in the fluid may contribute to the onset of flow instability. On the other hand, mixing is enhanced by fluid lamination when the actuating voltages are not in-phase. For ź ź 0, fluid tends to flow first from one inlet directly into the other before moving to the opposite side of the diverging section in the following cycle to form fluid striations. As the phase difference increases, mixing is improved due to a longer active duration of this mechanism. We find that the mixing performance always peaks at a phase difference of 0.75ź, and a diverging micromixer with a half-angle larger than 35° is preferred. Comparing to the unipolar actuation, bipolar actuation strengthens fluid lamellae and hence leads to higher mixing efficiency. Increasing the superimposed pressure head, on the other hand, weakens molecular diffusion and deteriorates mixing performance drastically.

Effect of Destroying High Pulsed Electric Field to Ascaris Suum Eggs

In order to investigate the effect of high power square-wave pulsed electric field (HPEF) on parasite eggs, Ascaris suum eggs are selected as an example. By changing the voltage, frequency, acting time of the pulse, electrode shape, and living environment of Ascaris suum eggs, this paper discusses the relationship between parameters of HPEF and the effect of destroying Ascaris suum eggs. Then the direct smear for microscopic examination is adopted for counting the death rate of Ascaris suum eggs. The research result shows that with fixed experiment conditions the death rate of Ascaris suum eggs increases with the increase of electric field voltage and acting frequency. Furthermore, the acting time has weak effect to the death rate, and the death rate with pin-pin electrode is the highest. When pulsed voltage is fixed and higher than 60kV with pin-pin electrode, the death rate is always higher than 80%. However, the death rate in pin-board electrode is inconsistent. The experiment results indicate that HPEF has effective impact on Ascaris suum eggs while feasible processing parameters are selected, so it can be used in destroying Ascaris suum eggs and some other parasite eggs.

Elecrohydrodynamical characteristics of liquid film motor driven by a square-wave electrophoresis electric field

Liquid film motor as a novel experimental device will play an important role in basic research and technology applications. In-depth theoretical studies on its electro-hydrodynamics (EHD) motions under various conditions are of great significance. In current paper, the dynamical characteristics of the liquid film motor driven by a square-wave electrophoresis electric field perpendicular to a uniform constant external electric field are investigated. Space-time dependence of the film's rotation linear velocity is derived analytically. The theoretical results indicate that a symmetrical reciprocating rotation in the film gradually converts to a vibration as the frequency of the electrophoresis electric field increases. This not only helps us understand the physical origin of the vibration of the liquid film motor, but also provides a new option to design a liquid film mixer in the application.

Comment on “Universal yield stress equation for transient response of zeolite based electrorheological fluid”

We comment on the transient process of an electrorheological (ER) fluid under square-wave electric field excitation by analyzing its electric field-induced stable shear stress at a different shear rate. Using a critical electric field in the ER system, we find that the universal yield stress equation collapses the reported experimental data onto a single curve very well.

Chaotic mixing in microchannels via low frequency switching transverse electroosmotic flow generated on integrated microelectrodes

In this paper we present a numerical and experimental investigation of a chaotic mixer in a microchannel via low frequency switching transverse electroosmotic flow. By applying a low frequency, square-wave electric field to a pair of parallel electrodes placed at the bottom of the channel, a complex 3D spatial and time-dependence flow was generated to stretch and fold the fluid. This significantly enhanced the mixing effect. The mixing mechanism was first investigated by numerical and experimental analysis. The effects of operational parameters such as flow rate, frequency, and amplitude of the applied voltage have also been investigated. It is found that the best mixing performance is achieved when the frequency is around 1 Hz, and the required mixing length is about 1.5 mm for the case of applied electric potential 5 V peak-to-peak and flow rate 75 microL h(-1). The mixing performance was significantly enhanced when the applied electric potential increased or the flow rate of fluids decreased.

Measurement of Structural Changes in Tetragonal PZT Ceramics under Static and Cyclic Electric Fields Using a Laboratory X-ray Diffractometer

In situ structural characterization techniques that are capable of characterizing piezoelectric ceramics under different electrical loading conditions are important to understand the behavior of materials during their use. In this work, we report the use of a laboratory X-ray diffractometer for the measurement of various structural changes in tetragonal La-doped lead zirconate titanate (PZT) ceramics under the application of static and cyclic electric fields. The changes in the volume fractions of the 90 degrees domains parallel to the electric field direction are calculated from the intensities of the {002} diffraction peaks. In addition, the components of lattice strains are monitored from the changes in the (111) crystallographic planes. It is observed that, under the application of static electric fields, both 90 degrees domain switching and the 111 lattice strains showed similarity with the macroscopic strain-electric field hystersis loop. To measure the structural changes under cyclic electric fields, a time-resolved X-ray diffraction technique was used. Under application of a square-wave electric field of amplitude +/-650 V/mm and frequency 0.3 Hz, a change of approximately 5% in the volume fraction of the 90 degrees domains and approximately 0.07% strain of the 111 lattice planes are observed. Both the amount of 90 degrees domain switching and the 111 lattice strains are observed to increase with an increase in the amplitude of the cyclic electric field. The implications of the measured structural changes for the macroscopic piezoelectric properties of ceramics are discussed.

Electromechanical identification of molecules adsorbed on microcantilevers

An alternating current was applied to a gold-coated silicon microcantilever in a sodium chloride solution. The electric field applied through the gold layer attracts oppositely charged ions onto the cantilever, and the resulting variation of surface charges induces changes in the surface stress that result in oscillation of the cantilever. The bending profiles of cantilevers coated with 1-mercaptoethanol, 1-mercaptopropanol, and 1-mercaptohexanol excited by a square-wave electric field depended on the chain lengths of the layers: a layer comprising longer hydrocarbon chains more strongly hinders ions from being adsorbed on the gold layer, resulting in the cantilever bending more slowly.