Applied Ac Electric Field Research Articles

Disorder-Mediated Electron Valley Resonance in Carbon Nanotube Quantum Dots

We propose a scheme for coherent rotation of the valley isospin of a single electron confined in a carbon nanotube quantum dot. The scheme exploits the ubiquitous atomic disorder of the nanotube crystal lattice, which induces time-dependent valley mixing as the confined electron is pushed back and forth along the nanotube axis by an applied ac electric field. Using experimentally determined values for the disorder strength we estimate that valley Rabi oscillations with a period on the nanosecond time scale are feasible. The valley resonance effect can be detected in the electric current through a double quantum dot in the single-electron transport regime.

Converse magnetoelectric effect in nano-microscale lead-free multiferroic composite

Nontoxic lead-free multiferroic magnetoelectric composites were successfully prepared by incorporating the dispersed 0.15Ni 0.98Co 0.02Fe 2O 4 (NCF) ferromagnetic nanoparticles into 0.85(K 0.5Na 0.5)NbO 3–LiSbO 3 (KNN–LS) ferroelectric micromatrix. The composites show ferroelectric behaviors and magnetic characteristics. The converse magnetoelectric effect (CME) characteristics with the driving electric field, frequency and bias magnetic field ( H Bias) were investigated in detail by using double coils at room temperature. The CME behaviors are strongly dependent on the driving electric field, frequency and H Bias. Large CME coefficient (2.21 × 10 −10 s/m) was obtained at low frequency and low magnetic bias field (800 Oe). The induced saturation magnetization ( δM) has an excellent linear relationship with the applied ac electric field with amplitude varying from 7 to 73 V/cm. The CME coefficient increases initially with the increase in H Bias and then decreases with the further increase in the field.

Impacts of Temperature and Frequency on the Dielectric Properties for Insight into the Nature of the Charge Transports in the Tl2S Layered Single Crystals

Investigation of the electric properties of semi-conducting materials in an applied ac electric fields gives information about the nature of charge transport and localized states in the forbidden gap. Layered crystals usually contain structural defects, such as dislocations and vacancies that may form a high density of localized states near the Fermi level. So, the current study was carried out for insight into the dielectric Properties of Tl2S layered single crystals. These properties were studied using the ac measurements in the low temperatures ranging from 77 to 300 K. The real part of dielectric constant e?, imaginary part of dielectric constant e?, the dissipation factor tan δ and the alternating current conductivity σac were measured in an applied ac electric field of frequencies extending from 2.5 to 50 kHz. Based on the dependencies of these dielectric parameters on both the frequency and temperature, the dielectric properties of the crystals under investigation were elucidated and analyzed. The ac conductivity was found to obey the power law σac(ω) = Aωs with which the values of the exponent s were evaluated to be less than unity in the range 0.21 ≥ s ≥ 0.19. Furthermore, it was found that the temperature dependence of ac conductivity follows the Arrhenius relation via which the impact of temperature on the electrical processes in an applied ac electric field was illustrated and analyzed. The influences of temperature and frequency on both the exponent s and band gap were also discussed in this investigation.

Impacts of Temperature and Frequency on the Dielectric Properties for Insight into the Nature of the Charge Transports in the Tl2S Layered Single Crystals

Investigation of the electric properties of semi-conducting materials in an applied ac electric fields gives information about the nature of charge transport and localized states in the forbidden gap. Layered crystals usually contain structural defects, such as dislocations and vacancies that may form a high density of localized states near the Fermi level. So, the current study was carried out for insight into the dielectric Properties of Tl2S layered single crystals. These properties were studied using the ac measurements in the low temperatures ranging from 77 to 300 K. The real part of dielectric constant ε?, imaginary part of dielectric constant ε?, the dissipation factor tan δ and the alternating current conductivity σac were measured in an applied ac electric field of frequencies extending from 2.5 to 50 kHz. Based on the dependencies of these dielectric parameters on both the frequency and temperature, the dielectric properties of the crystals under investigation were elucidated and analyzed. The ac conductivity was found to obey the power law σac(ω) = Aωs with which the values of the exponent s were evaluated to be less than unity in the range 0.21 ≥ s ≥ 0.19. Furthermore, it was found that the temperature dependence of ac conductivity follows the Arrhenius relation via which the impact of temperature on the electrical processes in an applied ac electric field was illustrated and analyzed. The influences of temperature and frequency on both the exponent s and band gap were also discussed in this investigation.

Effect of Application of AC Electric Field on Operation of a Phase-Separable Type Reaction Process Using Polyethylene Glycol

Effect of Application of AC Electric Field on Operation of a Phase-Separable Type Reaction Process Using Polyethylene Glycol

電界砥粒制御技術を適用したガラス基板の高効率研磨技術の開発

This paper deals with the development of a novel polishing technique for the glass substrate for electric devices by applying AC electric field. In order to grasp the movements of the slurry under AC electric field, we have observed slurry behaviors with an observation device we developed, and found that the slurry was smoothly led to the polishing area by AC electric field. Furthermore, effectiveness of the slurry distribution on the polishing area increased by 12%. Polishing rate also increased 22% compared to the conventional polishing when AC electric field was applied. This will contribute to the reduction of the consumption of the cerium oxide abrasives.

Electric-field-induced dielectric response and magnetization in nano–microscale lead-free multiferroic composite

A new kind of nano/microscale lead-free multiferroic composite with a formal of 0.4CoFe2O4–0.6[0.948(K0.5Na0.5)NbO3–0.052LiSbO3] was prepared. The electric-field-induced dielectric (EID) and magnetization (EIM) behaviors were systemically investigated for this 0–3-type structured multiferroic ME composite. Significant electric-field-induced effects were obtained with a high tunability and a large EIM coefficient, which the former has a value of K = 3.35% under the low dc electric-field of 2 kV/cm and the later is in excess of 2.15 × 10−10 s/m at a low frequency of 1.0 kHz with a low magnetic bias field of 2000 Oe for this composite. It is also proved that its EIM behavior is strongly dependent on the bias magnetic field HBias and the frequency of driving electric-field. The measured EIM has an excellent linear relationship with the applied ac electric-field with amplitude varying from 7.1 to 73.6 V/cm. The electric-field-induced effects indicate that the 0–3-type particulate ME composites not only have physical interest but also have potential practical use.

Numerical study of deformations induced by ac electric field in insulating flexoelectric nematic layers

AbstractThe influence of the frequency f of applied ac electric field on the time dependence of electric field induced deformations of homeotropic nematic layers is studied numerically. Three kinds of nematic liquid crystals were considered: non-flexoelectric nematic with negative dielectric anisotropy, Δɛ < 0dielectrically compensated nematic (Δɛ = 0) possessing flexoelectric properties determined by the positive sum of flexoelectric coefficients e = e11 + e33 > 0nematic characterised by both Δɛ < 0 and e > 0.It was found that at sufficiently low frequencies, the deformations varied with time. The deformations of purely dielectric nature had the period 1/(2f). When the frequency was increased, a stationary director distribution was achieved, determined by the rms value of the ac voltage. The time period of purely flexoelectric distortions was equal to 1/f. There was a well defined cut-off frequency above which these deformations vanished. In the case of dielectrically anisotropic and flexoelectric nematic, the flexoelectric contribution vanished above a critical frequency and the deformation of dielectric nature stabilized at high frequencies.

폴리에틸렌으로 피복된 전선화염의 전파에 교류전기장이 미치는 영향에 관한 실험적 연구

본 연구는 교류전기장이 인가된 전선에서의 화염전파특성에 전기장이 미치는 영향에 대한 실험적 연구이다. 폴리에틸렌으로 피복된 전선에서 인가된 교류전압과 주파수에 따라 화염전파율을 도출하였다. 그리고 화염전파는 선형적 화염 전파와 비선형적으로 가속된 화염 전파로 구분되어졌다. 이것은 전선에 인가된 교류전기장에 따라 형성된 전기장 세기의 축방향 분포가 원인이 된다. 그리고 기울어진 전선화염의 화염전파율이 상대적으로 높게 나타났다. 이러한 현상은 온도균형메커니즘으로 설명이 가능하다.

A new dispersion method for the preparation of polymer/organoclay nanocomposite in the electric fields

A new electric application method was developed to prepare epoxy/organoclay nanocomposite for the electrical insulation in the ac electric fields and it could be also used in the field of various viscous polymer/organoclay systems. The applied ac electric field condition was as follows; (1) inter-electrode distance: 40 mm, (2) application voltage: 3-11 kV, (3) frequency: 60-1,000 Hz, and (4) application time: 0-60 min. To characterize the epoxy/clay nanocomposite, WAXS and TEM analyses were performed. In order to explain how the organic modifier affects the exfoliation phenomena, a mechanism of the oscillating collision of the quaternary ammonium head was proposed and the effects of the ac voltage and frequency and the organoclay content were studied.

Effect of AC electric fields on the stabilization of premixed bunsen flames

The stabilization characteristics of laminar premixed bunsen flames have been investigated experimentally for stoichiometric methane–air mixture by applying AC voltage to the nozzle with the single-electrode configuration. The detachment velocity either at blowoff or partial-detachment has been measured by varying the applied voltage and frequency of AC. The result showed that the detachment velocity increased with the applied AC electric fields, such that the flame could be nozzle-attached even over five times of the blowoff velocity without having electric fields. There existed four distinct regimes depending on applied AC voltage and frequency. In the low voltage regime, the threshold condition of AC electric fields was identified, below which the effect of electric fields on the detachment velocity is minimal. In the moderate voltage regime, the flame base oscillated with the frequency synchronized to AC frequency and the detachment velocity increased linearly with the applied AC voltage and nonlinearly with the frequency. In the high voltage regime, two different sub-regimes depending on AC frequency were observed. For relatively low frequency, the flame base oscillated with the applied AC frequency together with the half frequency and the variation of the detachment velocity was insensitive to the applied voltage. For relatively high frequency, the stabilization of the flame was significantly affected by the generation of streamers and the detachment velocity decreased with the applied voltage.

Separation of viable and nonviable animal cell using dielectrophoretic filter

Selective separation of cells using dielectrophoresis (DEP) has recently been studied and methods have been proposed. However, these methods are not applicable to large-scale separation because they cannot be performed efficiently. In DEP separation, the DEP force is effective only when it is applied close to the electrodes. Utilizing a DEP filter is a solution for large-scale separation. In this article, the separation efficiency for viable and nonviable cells in a DEP filter was examined. The effects of an applied AC electric field frequency and the gradient of the squared electric field intensity on a DEP velocity for the viable and nonviable animal cells (3-2H3 cell) were discussed. The frequency response of the DEP velocity differed between the viable and the nonviable cells. We deducted an empirical equation that can be used as guiding principle for the DEP separation. The results indicate that the viable and the nonviable cells were separated using the DEP filter, and the best operating conditions such as the applied voltage and the flow rate were discussed.

Orientation and Dynamics of ZnO Nanorod Liquid Crystals in Electric Fields

ZnO nanorod polymer hybrids (i.e., ZnO nanorods coated with a block copolymer with a short anchor block (dopamine) and a longer solubilizing block of polystyrene (PS)) form liquid crystalline (LC) phases if they are dispersed at high concentration e.g., in a PS oligomer matrix. Due to the high mobility of the low T(g) -matrix the nanorod polymer hybrids show a switching behavior under an applied AC electric field. Hence, the orientation of the nanorod mesogens can be changed from planar (parallel to the substrate) to homeotropic (perpendicular) in full analogy to the switching of low molecular liquid crystals in an electric field. Dielectric measurements show that such a switching is mainly due to the cooperative LC behavior, because the rods themselves exhibit only a very small effective dipole moment. The process can be investigated by polarizing microscopy. SEM images show the orientations of the individual nanorods, which correspond to the Fredericks transition well known for liquid crystals aligned in an electric field. This was the first time such a transition could be visualized by electron microscopy due to the large nanorod mesogens. The observation is interesting to orient nanorods perpendicular to an electrode and can help to improve optoelectronic devices.

Mechanism for giant electro-optic response of porphyrin J-aggregates in polymer film and aqueous solution

We report the dependence of the polarizability difference Δα on the orientational distribution of porphyrin J-aggregates. For quasi-one-dimensionally oriented aggregates in a polymer film, the red shift in Y ∥ F configuration was about 2 to 3 times smaller than that in Y ∥ F configuration, where Y is the orientational direction of the J-aggregates and F is the applied AC electric field vector. For an aqueous solution where J-aggregates were three-dimensionally oriented, the exciton band showed an electric-field-induced broadening. In addition, a red-shifted signal for two-dimensionally oriented aggregates in the polymer film was reduced by one order of magnitude at 77K compared with that at room temperature. These results were explained reasonably well by the molecular rearrangement model, which was applied to a variety of orientational distributions.

Room temperature electrocaloric effect on PbZr0.8Ti0.2O3 thin film

A phase field model based on the time-dependent Ginburg–Landau equation (TDGL) is developed to investigate the electrocaloric effect (ECE) of PbZr0.8Ti0.2O3 (PZT) thin film with a multidomain structure. The rhombohedral domain morphology is obtained through numerically solving the TDGL equation with periodic boundary conditions at room temperature. Then the ECE of PZT thin film is investigated by the thermodynamics analysis. It is shown that a great ECE exists with an applied ac electric field at room temperature. The magnitude of ECE greatly depends on the external applied electric field and becomes a periodic time-dependent quantity. The theoretical calculations also reveal that both compressive and tensile misfit strains caused by the mismatch between the film and the substrate can largely affect the electrocaloric properties. It reveals that the compressive substrate strain enhances the ECE of PZT thin film while the tensile substrate strain suppresses it.

Mesoscopic relaxation time of dynamic image correlation spectroscopy

Dynamical images contain useful information of how the objects behave in time and space. When the system is in biological fluids, the motion of the object is much over-damped; the relaxation time is the characteristics in a diffusive time scale. We have found dynamical states of melting and forming of small nematic domains (10—30 μm) that are exhibited in the suspensions of fd-viruses under applied AC electric field amplitude at low frequency. Dynamic image correlation function is used for extracting the mes- oscopic relaxation times of the dynamical states, which can be employed as an application to other dynamic imaging process of biologically relevant soft condensed matter and biomedical systems.

Modeling the effects of microencapsulation on the electro-optic behavior of polymer cholesteric liquid crystal flakes

A method for modeling the effect of microencapsulation on the electro-optical behavior of polymer cholesteric liquid crystal (PCLC) flakes suspended in a host fluid is introduced. Several microencapsulation configurations in an applied ac electric field are investigated using COMSOL MULTIPHYSICS software in combination with an analytical model. The field acting on the flakes is significantly altered as various encapsulant materials and boundary conditions are explored. The modeling predicts that test cells with multiple materials in the electric field path can have a wide range of electro-optic responses in ac electric fields. Both theoretical predictions and experimental evidence show that for PCLC flake reorientation to occur due to Maxwell–Wagner polarization, a reasonably strong electric field must be present along with at least moderately dissimilar PCLC flake and host fluid material dielectric constants and conductivities. For materials with low dielectric constants, electrophoretic behavior is observed under dc drive conditions at high field strengths for all evaluated microencapsulation configurations. This modeling method is shown to be a useful predictive tool for developing switchable particle devices that use microencapsulated dielectric particles in a host fluid medium.

Nonlinear Conductivity and Permittivity Spectra of Ion Conducting Glasses

Abstract We have measured third-order conductivity and permittivity spectra of a Li2O · Al2O3 · 4 SiO2 glass and of a 0.15 Na2O · 0.85 GeO2 glass by applying ac electric fields up to 100 kV cm−1. For the application of these high fields, the glass samples are interfaced with highly conductive liquid electrolyte solutions. In this field range, the electrical response due to ion dynamics in the bulk of a glass sample is weakly nonlinear, while the electrical reponse due to ion transport across the interface between glass sample and liquid electrolyte is strongly nonlinear. For both glasses, the real part of the third-order conductivity is characterised by a change in sign in a frequency range where the diffusive bulk ion dynamics passes over into the subdiffusive bulk ion dynamics. On the other hand, the real part of the third-order permittivity spectra is characterised by a change in sign at lower frequencies where ion transport across the glass / liquid electrolyte interface passes over into the bulk ion transport. We show that these changes in sign can be rationalised by considering an equivalent circuit for a disordered solid ion conductor interfaced with a highly conductive liquid. In this circuit, the bulk and interfacial resistances are assumed to decrease with increasing voltage.

Enhancement of electrokinetically driven microfluidic T‐mixer using frequency modulated electric field and channel geometry effects

This study reports improved electrokinetically driven microfluidic T-mixers to enhance their mixing efficiency. Enhancement of electrokinetic microfluidic T-mixers is achieved using (i) an active approach of utilizing a pulsating EOF, and (ii) a passive approach of using the channel geometry effect with patterned blocks. PDMS-based electrokinetic T-mixers of different designs were fabricated. Experimental measurements were carried out using Rhodamine B to examine the mixing performance and the micro-particle image velocimetry technique to characterize the electrokinetic flow velocity field. Scaling analysis provides an effective frequency range of applied AC electric field. Results show that for a T-mixer of 10 mm mixing length, utilizing frequency modulated electric field and channel geometry effects can increase the mixing efficiency from 50 to 90%. In addition, numerical simulations were performed to analyze the mixing process in the electrokinetic T-mixers with various designs. The simulation results were compared with the experimental data, and reasonable agreement was found.

Evidence for directed self-assembly of quantum dots in a nematic liquid crystal

Assembling quantum dots (QDs) into nanoscale configurations over macroscopic dimensions is an important goal to realizing their electro-optical potential. In this Rapid Communication, we present a detailed study of a pentylcyanobiphenyl liquid crystal (LC) and a CdS QD colloidal dispersion by probing the dielectric property epsilon and relaxation as a function of an applied ac electric field Eac. In principle, dispersing QDs in a nematic LC medium can direct the dots to align in nearly one-dimensional chainlike structures along the nematic director and these assemblies of QDs can be directed by external electric fields. In a uniform planar aligned cell, the Fréedericksz switching of the LC+QDs appears as a two-step process with the same initial switching field as the bulk but with the final epsilon value larger than that for an aligned bulk LC. The relaxation of epsilon immediately following the removal of Eac follows a single-exponential decay to its original value that is slower than the bulk but becomes progressively faster with increasing Eac, eventually saturating. These results suggest that the arrangement of the QDs is mediated by the LC.