Applied Ac Field Research Articles

Theoretical Analysis and Experimental Determination of the Relationships Between the Parameters of the Electric Field Pulse Required to Electroporate the Cells

Here, theoretical relationships between the parameters of the electric pulse, which is necessary to porate the cell by electric pulse of various shapes, have been obtained. The theoretical curves were compared with the experimental relationships. Experiments were carried out with human erythrocytes, Chinese hamster ovary and mouse hepatoma MH-22A cells. The fraction of electroporated MH-22A cells was determined from the extent of the release of intracellular potassium ions and erythrocytes-from the extent of their hemolysis after long (20-24 h) incubation in 0.63% NaCl solution at 4°C. The dependence of the fraction of electroporated cells on the amplitude of the electric field pulse was determined for pulses with the duration from 95 ns to 2 ms. The shapes of theoretical dependencies are in agreement with experimental ones. The cell poration time depended on the intensity of the pulse: the shorter the pulse duration, the higher the electric field strength has to be. This dependence is much more pronounced for pulses . For example, if the pulse amplitude required to electroporate 50% of human erythrocytes increased from 1.0 to 1.76 kV/cm, when the duration of a square-wave pulse was reduced from 2 ms to 20 μs, it increased from 3 to 12 kV/cm, when the pulse duration was reduced from 950 to 95 ns. The relationships between the electric field strength required for electroporation and the frequency of the applied ac field were calculated for different pulselengths. It has been obtained that although the electric field strength is constant for frequencies but its value depends on the pulselength decreasing with increasing pulse duration. At higher frequencies, electric field strength is dependent on the frequency of the ac field.

Fe-based nanoparticles as tunable magnetic particle hyperthermia agents

Magnetic hyperthermia, an alternative anticancer modality, is influenced by the composition, size, magnetic properties, and degree of aggregation of the corresponding nanoparticle heating agents. Here, we attempt to evaluate the AC magnetic field heating response of Fe-based nanoparticles prepared by solar physical vapor deposition, a facile, high-yield methodology. Nanoparticle systems were grown by evaporating targets of Fe and Fe3O4 with different stoichiometry. It is observed that Fe3O4 nanoparticles residing in the magnetic monodomain region exhibit increased heating efficiency together with high specific loss power values above 0.9 kW/g at 765 kHz and 24 kA/m, compared with that of 0.1 kW/g for zero-valent Fe nanoparticles under the same conditions. The enhanced performance of Fe3O4 nanoparticles under the range of field explored (12–24 kA/m) may be attributed to the activation of a magnetic hysteresis loss mechanism when the applied AC field surpasses the particle anisotropy field at H ≥ 0.5HA. This is also illustrated by the smaller coercivity of Fe3O4 nanoparticles compared with that of their Fe counterparts. Therefore, understanding the interconnection between intrinsic parameters (composition, size and magnetic properties), the dosage (concentration, volume) and the intensity and frequency of the AC field can lead to essential design guidelines for in vitro, in vivo, and clinical applications of magnetic nanoparticles for hyperthermia.

Dielectrophoresis flow control in microchannels

Abstract The control of flow in microscale is one of the most important problems in microfluidic devices, which in particular, are used as micro heat exchangers. The use of electric field is one of the efficient methods of control of dielectric liquid flow in microscale. The electric field influences liquid flow by the EHD force which affects liquid behaviour in terms of the flow rate and pressure. The EHD force consists of three components: the first is the electrostatic force due to free charges present in the liquid, the next one is the force due to the gradient of permittivity of material, and the third one is caused by the change in the electric field intensity. The EHD force is used also in many commercial devices, for example EHD pumps or dielectrophoretic separators. An own approach to apply the EHD force to control the liquid flow rate is presented in this paper. Authors paid a close attention to the dielectrophoresis effect. Dielectric liquid in a non-uniform electric field tends to drift/migrate towards the region of high electric field intensity. With decreasing the electrode dimensions, the dielectrophoresis force becomes relatively stronger. For the dimensions under 400 μm the dielectrophoresis phenomenon can be used for control and actuation of the liquid flow in microchannels. The originally developed design of such flow controller is presented in this paper. The experimental investigations covered flow rate measurement of 2-propanol in microchannel flow controller with application of AC field. It was showed that the dielectrophoresis phenomenon could effectively control the flow. The results for distilled water are also comparatively discussed in the paper.

19.6L: Late‐News Paper: How to Fabricate Much Brighter AC Electroluminescent Lamps: Optimizing the Alignment of the Emitting ZnS:Cu Phosphor Particles to the AC Field

AbstractThe photoluminescence and electroluminescence of loose ZnS:Cu crystals scattered on an interdigitated electrode substrate have been studied under 366nm UV light excitation and or under an applied AC field. From the response of the ZnS:Cu crystals to the AC field and their movement in the field it is shown that a greater understanding of the factors affecting ACEL panel performance can be gained. The findings light the way to the fabrication of very bright panels and a suggestion can be made to the expected luminescence of optimised ACEL lamps

Dynamic magnetization reversal in dipole systems

The possibility of magnetization reversal in two different systems of magnetic dipoles by preliminary excitation of certain oscillatory regimes is demonstrated using numerical analysis of bistable states of these systems. Cyclic magnetization reversal of the systems is executed by sequential alternation of the frequency of the applied ac field. The interaction of two ring-shaped dipole systems is analyzed and peculiarities of the change in the total magnetic moments induced by this interaction are revealed.

Alternating current-dielectrophoresis driven on-chip collection and chaining of green microalgae in freshwaters

The capability of the AC dielectrophoresis (DEP) for on-chip capture and chaining of microalgae suspended in freshwaters was evaluated. The effects of freshwater composition as well as the electric field voltage, frequency, and duration, on the dielectrophoretic response of microalga Chlamydomonas reinhardtii were characterized systematically. Highest efficiency of cell alignment in one-dimensional arrays, determined by the percentage of cells in chain and the chain length, was obtained at AC-field of 20 V mm(-1) and 1 kHz applied for 600 s. The DEP response and cell alignment of C. reinhardtii in water sampled from lake, pond, and river, as well as model media were affected by the chemical composition of the media. In the model media, the efficiency of DEP chaining was negatively correlated to the conductivity of the cell suspensions, being higher in suspensions with low conductivity. The cells suspended in freshwaters, however, showed anomalously high chaining at long exposure times. High concentrations of nitrate and dissolved organic matter decrease cell chaining efficiency, while phosphate and citrate concentrations increase it and favor formation of longer chains. Importantly, the application of AC-field had no effect on algal autofluorescence, cell membrane damage, or oxidative stress damages in C. reinhardtii.

Dielectric spectroscopic studies of boron subphthalocyanine chloride thin films

Boron subphthalocyanine chloride (Cl-BsubPc) thin film have been deposited by thermal evaporation technique and studied for structural and dielectric properties. AFM study indicates the formation of uniform and cracks free films. To study the dielectric properties as function of both frequency and voltage, Al/Cl-BsubPc/Al heterostructure has been fabricated. The impedance-frequency study indicates the formation of space charge region in lower frequency range. The conduction mechanism in Cl-BSubPc film, under applied ac field, found to be electronic hopping. The mobility and charge carrier concentration of Cl-BsubPc films have also been measured using capacitance techniques.

Control of transport in two-dimensional systems via dynamical decoupling of degrees of freedom with quasiperiodic driving fields

We consider the problem of the control of transport in higher-dimensional periodic structures by applied ac fields. In a generic crystal, transverse degrees of freedom are coupled, and this makes the control of motion difficult to implement. We show, both with simulations and with an analytical functional expansion on the driving amplitudes, that the use of quasiperiodic driving significantly suppresses the coupling between transverse degrees of freedom. This allows a precise control of the transport, and does not require a detailed knowledge of the crystal geometry.

Magnetic relaxation behavior of a spatially closed dysprosium(III) phthalocyaninato double-decker complex

The SMM properties of the spatially closed Dy(III) double-decker Pc complex Dy(obPc)2 (1), which is equivalent to a pseudo dinuclear complex, are reported. Complex 1 crystallized with ethanol in the crystal lattice in the monoclinic space group P21/n and was isomorphous with Tb(obPc)2 (3), which is arranged in a dimer structure along the b axis. The intermetallic Dy-Dy distance was determined to be 0.756 nm. χMT versus T plots for 1 decreased with a decrease in T, which suggests the existence of an antiferromagnetic (AF) interaction between the Dy3+ ions. The M-H curve for 1 at 1.8 K showed magnetic hysteresis. In ac susceptibility measurements on a powder sample of 1, which were dependent on the applied ac field, indicating that 1 is an single molecule magnet (SMM), a maximum appeared at 22 K at an ac frequency (f) of 1488 Hz. The shape of the peaks drastically changed, and the peaks did not shift when an Hdc large enough to suppress the quantum tunneling of the magnetization (QTM) was applied. The energy barrier (Δ/hc) was estimated to be 44 cm−1 with a pre-exponential factor (τ0) of 1.6 × 10−5 s from an Arrhenius plot. Our results suggest that the SMM/magnetic properties of 1 significantly change in a dc magnetic field. These relaxation mechanisms are related to the energy gap of the ground state and to QTM.

Suppression of Inelastic Electron-Electron Scattering in Anderson Insulators

We report on measurements of absorption from applied ac fields in Anderson-localized indium-oxide films. The absorption shows a roll-off at a frequency that is much smaller than the electron-electron scattering rate measured at the same temperature in diffusive samples of this material. These results are interpreted as evidence for discreteness of the energy spectrum.

Critical current density measurement of thin films by AC susceptibility based on the penetration parameter h

We have numerically proved that the dependence of AC susceptibility χ of a E(J) power law superconducting thin disc on many parameters can be reduced to one penetration parameter h, with E the electric field and J the current density. Based on this result, we propose a way of measuring the critical current density Jc of superconducting thin films by AC susceptibility. Compared with the normally used method based on the peak of the imaginary part, our method uses a much larger range of the AC susceptibility curve, thus allowing determination of the temperature (T) dependence of Jc from a normally applied χ(T) measurement. A fitting equation Jc=1.9Ha∣χ′∣0.69/d, −0.4<χ′<−0.001 derived from the critical state case (Bean model) can be used in most situations, where Ha is the amplitude of the applied AC field, χ′ is the real part of the normalized susceptibility and d is the thickness of the film. The method is valid for the cases where the film is fully penetrated. We also discuss how the finite London penetration depth affects the susceptibility when the film is screened. Measurements with varying T, Ha and DC background field Hdc are performed to support the arguments.

Flux avalanches triggered by AC magnetic fields in superconducting thin films

Flux avalanches are known to occur as a consequence of thermomagnetic instabilities. Some of their fingerprints are jumps in magnetization curves, or a paramagnetic reentrance in AC susceptibility measurements. In this work we have studied flux avalanches triggered by an AC field cycle by means of AC susceptibility and residual magnetization after an applied AC field measured as a function of an AC excitation field (h). These measurements allow comparing both results with magneto-optical imaging carried out in similar conditions. The results show a correspondence for the onset of the avalanche activity, as well as between the residual magnetic moment and the mean gray value calculated from the magneto-optical images in the remanent state.

Effect of incubation in simulated body fluid on dielectric and photoluminescence properties of nano-hydroxyapatite ceramic doped with strontium ions

This paper reports the dielectric and photoluminescence measurements of ossiointegrated strontium doped hydroxyapatite bioceramic. The study on invitro bioactivity of Sr-HAp is carried out by using modified simulated body fluid. Dielectric properties of these ossiointegrated samples are studied in the frequency range 10 Hz to 1 MHz at room temperature. Dielectric constant is found to be decreasing with increase in incubation period and frequency of applied ac field. Higher the period of incubation and applied ac frequency, higher is the dielectric loss. AC conductivity shows frequency independent behaviour for all samples in lower frequency region and then increases linearly with increase in frequency. Sample incubated for longer duration shows higher conductivity. The optical properties of incubated Sr-HAp samples are also investigated with photoluminescence (PL) technique. The PL study shows the blue emission at around 476 nm when excited at 409 nm. The PL in tensity increases with increase in incubation duration and Sr-substitution.

Measuring electrical parameters of ferroelectric liquid crystals using universal current reversal method

The universal current reversal method is used for the simultaneous measurement of response time (τ), azimuthal angle (ϕo), spontaneous polarization (P S), and rotational viscosity (γϕ) of two ferroelectric liquid crystals (FLCs). The application of AC field in FLCs results in reorientational current, which is further analyzed to obtain various parameters. The variation in the parameters with temperature follows the typical trend predicted by the theory. The theoretical curve fits well into the experimental data. Its comparison with traditional current reversal method is confirmed to address certain limitations of that method.

Dynamic Resistance of YBCO-Coated Conductors in Applied AC Fields With DC Transport Currents and DC Background Fields

In order to predict heat loads in future saturable-core fault-current-limiting devices due to ac fringing fields, dynamic resistance in YBCO-coated conductors was measured at 77 K in peak ac fields up to 25 mT at 60 Hz and in dc fields up to 1 T. With the sample orientation set such that the conductor face was either parallel or perpendicular to the ac and dc applied fields, the dynamic resistance was measured at different fractions of the critical current to determine the relationship between the dc transport current and the applied fields. With respect to field orientation, the dynamic resistance for ac fields that were perpendicular to the conductor face was significantly higher than when the ac fields were parallel to the conductor face. It was also observed that the dynamic resistance: 1) increased with increasing fraction of the dc transport current to the critical current, 2) was proportional to the inverse of the critical current, and 3) demonstrated a linear dependence with the applied ac field once a threshold field was exceeded. This functional behavior was consistent with a critical state model for the dynamic resistance, but discrepancies in absolute value of the dynamic resistance suggested that further theoretical development is needed.

Field stability of piezoelectric shear properties in PIN-PMN-PT crystals under large drive field.

The coercive fields (E(C)) of Pb(In₀.₅Nb₀.₅)O₃-Pb(Mg(¹/₃)Nb(²/₃)O₃-PbTiO₃ (PIN-PMN-PT) ternary single crystals were found to be 5 kV/cm, double the value of binary Pb(Mg(¹/₃)Nb(²/₃)O₃-PbTiO₃ (PMNT) crystals, further increased to 6 to 9 kV/cm using Mn modifications. In addition to an increased EC, the acceptor modification resulted in the developed internal bias (E(int)), on the order of ~1 kV/cm. The piezoelectric shear properties of unmodified and Mn-modified PIN-PMN-PT crystals with various domain configurations were investigated. The shear piezoelectric coefficients and electromechanical coupling factors for different domain configurations were found to be >2000 pC/N and >0.85, respectively, with slightly reduced properties observed in Mn-modified tetragonal crystals. Fatigue/cycling tests performed on shearmode samples as a function of ac drive field level demonstrated that the allowable ac field levels (the maximum applied ac field before the occurrence of depolarization) were only ~2 kV/cm for unmodified crystals, less than half of their coercive field. Allowable ac drive levels were on the order of 4 to 6 kV/cm for Mn-modified crystals with rhombohedral/orthorhombic phase, further increased to 5 to 8 kV/cm in tetragonal crystals, because of their higher coercive fields. It is of particular interest that the allowable ac drive field level for Mn-modified crystals was found to be ≥ 60% of their coercive fields, because of the developed E(int), induced by the acceptor-oxygen vacancy defect dipoles.

Influence of electrical fields (AC and DC) on phytoremediation of metal polluted soils with rapeseed ( Brassica napus) and tobacco ( Nicotiana tabacum)

The combined use of electrokinetic remediation and phytoremediation to decontaminate soil polluted with heavy metals has been demonstrated in a laboratory-scale experiment. The plants species selected were rapeseed and tobacco. Three kinds of soil were used: un-contaminated soil from forest area (S1), artificially contaminated soil with 15 mg kg −1 Cd (S2) and multi-contaminated soil with Cd, Zn and Pb from an industrial area (S3). Three treatment conditions were applied to the plants growing in the experimental vessels: control (no electrical field), alternating current electrical field (AC, 1 V cm −1) and direct current electrical field (DC, 1 V cm −1) with switching polarity every 3 h. The electrical fields were applied for 30 d for rapeseed and 90 d for tobacco, each experiment had three replicates. After a total of 90 d growth for rapeseed and of 180 d for tobacco, the plants were harvested. The pH variation from anode to cathode was eliminated by switching the polarity of the DC field. The plants reacted differently under the applied electrical field. Rapeseed biomass was enhanced under the AC field and no negative effect was found under DC field. However, no enhancement of the tobacco biomass under the AC treatment was found. The DC field had a negative influence on biomass production on tobacco plants. In general, Cd content was higher in both species growing in S2 treated with AC field compared to the control. Metal uptake (Cd, Cu, Zn and Pb) per rapeseed plant shoot was enhanced by the application of AC field in all soils.

Frequency Dependent Electro-Optic Properties of Potassium Lithium Tantalate Niobate Single Crystal

Single crystals K0.95Li0.05Ta1-x Nb x O3 (KLTN) - x = 0.6 are grown and the transmission spectra show the UV absorption edge is about 400 nm for the transparent KLTN crystal sample. The refractive index and the frequency dependent of linear electro-optic coefficients of KLTN single crystals in the tetragonal phase are characterized at room temperature. The minimum deviation method is used for the refractive index measurements and the electro-optic properties have been investigated using the senarmont method and the auto scanning mach-zehnder interferometer technique. The EO measurements were taken with the continuous low frequency of applied ac field from 100 Hz to 100 KHz. Large electro-optic responses are observed and the coefficients, γ33 = 216.7 pm/V, γ13 = −21.2 pm/V, and γc = 242.9 pm/V at 1 kHz are measured for the crystals. The E-O properties show that the high quality KLTN single crystals have the potential in the field of optical modulation and deflection field devices.

Coupled domain structures in superconductor/ferromagnet Nb-Fe/garnet bilayers

We investigate the magnetic structure in a superconducting Nb and ferromagnetic garnet hybrid film. Direct magneto-optical observations reveal a strong interaction between the superconducting vortices in Nb and the magnetic domains in the garnet, resulting in a unique coupled domain structure. The cooperative motion of vortices and domain walls results in an enhanced pinning and a modified electromagnetic response of the hybrid similar to that in type I superconductors. Application of ac field, routinely used for equilibration of domains, leads to their significant contraction. Our calculations explain this effect by a domain shrinkage instability induced by the vortex annihilation around oscillating domain walls.

Chemical-Modification-Enhanced Dielectrophoretic Assembly of Controllable and Reversible Silica Submicrowires from Nanoparticles

In this article, the dielectrophoretic (DEP) assembly of chemically-modified silica nanoparticles (SiNPs) was introduced. Five types of surface-modified SiNPs, including OH-SiNPs, COOH-SiNPs, CH(3)HPO(2)-SiNPs, PEG-SiNPs, and NH(2)-SiNPs, have been investigated. After applying an ac field with relatively high intensity and frequency, it was shown that only COOH-SiNPs and CH(3)HPO(2)-SiNPs could be self-assembled on the microelectrodes by the DEP forces. The results indicated that the anionic group modification could obviously enhance the DEP self-assembly of SiNPs on the microelectrodes. Then the DEP assembly of CH(3)HPO(2)-SiNPs was selected as a representative to be investigated further. By using Rubpy dye doped in the core of the CH(3)HPO(2)-SiNPs, the assembly process was visualized in real time by inverse fluorescence microscopy. Precise control over the frequency of the applied ac field showed that the DEP forces can assemble CH(3)HPO(2)-SiNPs from aqueous suspensions into submicrowires, and it was found that the number of assembled submicrowires between the microelectrode gaps could be well controlled with reversibility. Furthermore, the DEP assembly process of CH(3)HPO(2)-SiNPs was sensitive to the pH of the dispersed medium. These findings would provide a way to circumvent the difficulty in controlling the dielectrophoretic assembly process of nanoparticles and offer application opportunities for the DEP assembly of chemically modified SiNPs.