A linear, single-stage, nanosecond pulse generator for delivering intense electric fields to biological loads

A compact pulse generator capable of producing high voltage pulses with halfmaximum widths as short as 2.5 ns and amplitudes as high as 5 kV has been developed to enable current and future in vivo and in vitro research into the effects of ultra-short, intense electric fields on biological matter. This pulse generator is small, simple, and free of saturable magnetic cores, which frequently introduce amplitude jitter and an undesirable correlation between amplitude and pulse width. In place of a non-linear pulse-forming network is a single-stage resonant network that drives a bank of junction recovery diodes. The diodes function as an opening switch that commutes current from an inductor to a resistive load. The use of air-core inductors in the resonant network results in a stable output pulse with an amplitude that scales linearly with input voltage and a pulse width that is independent of amplitude. The ability to scale the output amplitude independently of the pulse width simplifies the setup for experiments that require pulses with different electric field strengths but the same rise time and duration. Jurkat T lymphoblast cells exposed to 2.5 ns fields produced by this pulse generator showed an increasing degree of electropermeabilization with increasing pulse dosage and electric field intensity.     

Dynamic electric fields computed by finite elements

The authors describe how the MSC/MAGNETIC finite-element analysis program is used to compute electrostatic and electrodynamic fields. Example calculations are described for a capacitor with multiple lossy dielectric layers and for a high voltage bushing with a resistive coating. Comparison with classical results is given for the capacitor. The results for the simple lossy capacitor agree with conventional circuit theory. The results for the conductively coated bushing appear to show correctly the influence of conductivity on AC electric fields     

Sterilization of liquid foods by pulsed electric fields

Recent advances in the field of high-voltage pulse power technology have provided scope for the development of nonthermal sterilization methods free from the disadvantages commonly encountered with existing physical, chemical, or radiation sterilization. The flexibility allowed in the application of electrical energy can make high-field sterilization economical, compact, energy efficient, and environmentally acceptable. The main thrust of present research in this field is the application of high-field electric pulse technology to kill microorganisms in a manner consistent with development of industrial scale nonthermal sterilization methods     

Breakup of large water droplets by electric fields

The results are presented of an experimental study of the processes that lead to the breakup of a large water droplet doped with alcohol to approach the density of oil and immersed in an oil dielectric medium to which a strong electric field is applied. The study, which was carried out by means of photography, showed that the deformation of the droplets prior to breakup involves distinct characteristic stages of importance to the induction charging and to the ultimate charge separation phenomena. The experimental results show the conditions and the phenomena that lead to the breakup of an initially uncharged water droplet when subjected to an electric field that is not perfectly uniform and in a gravity field     

Analytical formula of induced electric fields in a spherical conductor by an ELF dipole magnetic field source

An analytical formula of induced electric field E in a spherical conductor by an ELF dipole magnetic field source is mathematically derived in vector form based on the equivalent mutlipole moment method with reexpansion technique (RE‐EMMM), where M _‖ and are parallel and perpendicular components of M , respectively. The validity of the formula is confirmed in the following three ways: (i) the derivation of the formula from the Sarvas equation with the reciprocity theorem derived by Eaton; (ii) the convergence of the formula to that of homogeneous magnetic field when M _‖ is located at the infinite distance; (iii) comparison of the analytical solutions with numerical solutions by RE‐EMMM. Furthermore, a formula for the trajectory, which satisfies E = 0 , is derived for the field by M _‖. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(3): 8– 17, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20739     

Ways to calculate electric fields in traction electric motor insulation by equivalent charge method

A procedure permitting one to calculate the electric fields in multilayer insulation based on the equivalent charge method is presented. Consideration of the new algorithm shows its fast response and proper accuracy.     

Inactivation of microorganisms by pulsed electric fields ofdifferent voltage waveforms

Processing foods with HV pulsed electric fields (PEF) is a new technology to inactivate microorganisms and denature enzymes with only a small increase in temperature. Introduction of this new technology will replace or complement conventional thermal processing methods. It will also provide consumers with safe, nutritious foods with fresh quality. For a given peak value of field intensity and amount of electric energy input, PEF inactivation of microorganisms is closely related to the waveform of applied pulses. Inactivation of microorganisms was studied with different waveshapes including exponential decay, oscillatory decay, square waves, and bipolar pulses. Microbial inactivation was tested in a parallel-plate static treatment chamber. Treatment field intensity ranged from 12 to 40 kV/cm while pulse length ranged from 30 to 180 μs. From the microbial test results, bipolar square-wave pulses are the most efficient in terms of microbial inactivation for commercial PEF pasteurization     

Dynamical modeling of cellular response to short-duration, high-intensity electric fields

The interaction of ultra-short duration, high-intensity electric fields with biological cells has recently begun to generate significant interest due to the possibility for non-thermal manipulation of cellular functions. It is clear that a full understanding requires a dynamical model for both electroporation and the electrostatic potential evolution. Here, dynamical aspects related to electroporation are reviewed. The simple model used in the literature is somewhat incorrect and unphysical for a variety of reasons. Our model for the pore formation energy, E(r), includes a dependence on pore population, density, a variable surface tension, and is dynamic in nature. It is shown that membranes can survive a strong electric pulse and recover provided the pore distribution has a relatively large spread. If, however, the population consists predominantly of larger radii pores, then irreversibility can result. Physically, such a distribution could arise if pores at adjacent sites coalesce. Results show that a finite time delay exists for pore formation, and can lead to a transient overshoot of the transmembrane potential V/sub mem/ beyond 1.0 V. Pore re-sealing is shown to consist of an initial fast process, a 10/sup -4/ s delay, followed by a much slower closing at a time constant of about 10/sup -1/ s. This establishes a time-window for effective killing by a second pulse.     

Rate of charging of spherical particles by monopolar ions in electric fields

This paper presents a numerical algorithm to simulate the charging dynamics of high-resistivity spherical particles by the ionic bombardment in an electric field. The algorithm is based on solving the Poisson equation, governing the electric field distribution, and the differential equation expressing the charge conservation law. The Poisson equation is solved be means of the finite-element method using the triangular discretization and the first of interpolation. The finite-volume method (in a version called the donor-cell method) is used to handle the charge conservation equation. Results of simulation are also presented and they illustrate the effect of different parameters on the charging dynamics. For high-conductivity particles, the charging rate is practically identical to that given by the Pauthernier formula. Charging of high-resistivity particles leads to more complicated solutions and is much slower.     

Modeling of conductive particle behavior in insulating fluidsaffected by DC electric fields

Several electrostatic technologies, such as separation of granular mixtures, flocking, printing, or biological cell manipulation, are based on the accurate control of conductive particle motion in insulating gases or liquids by means of relatively high DC electric fields. This paper is aimed at characterizing the behavior of such particles by numerical modeling of two aspects: (1) particle motion under the action of electric field forces and (2) insulation breakdown triggered by mobile particles. The equations of particle motion were written by taking into account both gravitational and drag forces, as well as the rebound at particle impact with the electrodes. If the particles move in ionized air, their charge varies in time. In that case, the equation of particle charge should be added to the mathematical model. The output data of the programs for numerical simulation of particle behavior are in good agreement with the available experimental results. Particle movements were shown to be influenced by the intensity of the electric field, by the density of the space charge, by size and mass density of the particles, as well as by their coefficient of restitution at impact with the electrodes. The conclusions regarding the behavior of conductive particles in insulating fluids are useful for the development of improved electrostatic separation technologies; they are of particular interest to all manufacturers of high-voltage equipment     

Charging of one or several cylindrical particles by monopolar ions in electric fields

In many electrostatic processes (precipitation of dust, separation of granular mixtures, spraying of powders) insulating particles are subjected to unipolar charging in the presence of other bodies. The present paper addresses this problem from both a computational and an experimental point of view, with the aim to extend an original numerical method of unipolar charge computation to the case of two or more particles, relatively close to each other. The charge acquired by cylinders of various dielectric constants was evaluated with a computer program based on the boundary element method of field analysis. The experimental setup simulated the charging conditions of millimeter-size calibrated cylinders of polyvinyl chloride in a roll-type electrostatic separator, the unipolar space charge being generated by a wire-type electrode. The experimental results, which were in good agreement with the theoretical predictions, put forward that the relative spacing between the particles changes the value of the saturation charge, an effect, which is stronger for particles of higher dielectric constant. These facts should be taken into account in the design of any electrostatic technology based on the corona charging of granular matter.     

Analysis of induced current density in grounded and ungrounded prolate spheroid models in concurrent ELF electric and magnetic fields

Analyzed in this paper is the induced current density in the homogeneous prolate spheroid model of a biological object exposed to concurrent 60‐Hz vertical electrical field (1 kV/m), and horizontal and vertical magnetic fields (1 to 5 μT) with different phase angle. The analysis has been carried out separately considering the presence of electric and magnetic fields. The current density induced by the electric field is calculated using the finite element method, whereas the current density induced by the magnetic fields is calculated with exact solution for the prolate spheriod model. The total induced current density is the vector sum of the current density components induced by the electric and magnetic fields. It is found that the density of the total current is determined by the vertical electric field and horizontal magnetic field. The horizontal magnetic field has an important effect on the total induced current density distribution. The distribution of the density of the total current varies with the phase difference between the vertical electric and horizontal magnetic fields. As the model gets close to the ground, however, the contribution of the horizontal magnetic field to the total induced current density is found to decrease. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 8–15, 2001     

Spherical harmonic series solution of fields excited by vertical electric dipole in earth-ionosphere cavity

The spherical harmonic series expression of electromagnetic fields excited by ELF/SLF vertical electric dipole in the spherical earth-ionosphere cavity is derived when the earth and ionosphere are regarded as non-ideal conductors. A method of speeding numerical convergence has been presented. The electromagnetic fields in the cavity are calculated by this algorithm, and the results show that the electromagnetic fields between the earth and the ionosphere are the sum of two traveling waves in the SLF band. Moreover, the results are in complete agreement with that of the well-known spherical second-order approximation in the SLF band. The electromagnetic fields in the cavity are a type of standing wave in the ELF band and the variation of the amplitude versus frequency coincides with Schumann’s resonance. __________ Translated from Chinese Journal of Radio Science, 2007, 22(2): 204–211 [译自: 电波科学学报]     

A review of studies on the electric field and the current induced in a human body exposed to electromagnetic fields

How high an electric field or current is induced inside a human body when exposed to an electromagnetic field has recently attracted much attention. The background for this is twofold; concern about the possible health effects of electromagnetic fields (usually called ‘EMF issues’), and their positive application to medical treatment or new research subjects. This paper reviews various aspects related to this topic in terms of the following items: basic formulas for field calculation, effect of electromagnetic fields, calculation methods, an Investigation Committee in the IEEJ, and future research subjects. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

On the screening of the electric field at the cathode surface by anelectron space charge at intense field emission

The paper considers the effect of the space charge of emitted electrons on the electric field at the tip of a field emitter. To analyze this phenomenon, the Poisson equation was solved numerically for a spherical vacuum diode with a field emission cathode. The dependence of the electric field on the geometric field has been compared with the known approximate dependencies, Strong screening of the electric field at the cathode by the space charge of emitted electrons at fields >5×10⁷ V/cm is noted. Based on the obtained dependencies of the actual field on the geometric one and using the SuperSAM code, the field emission occurring in a Muller projector has been simulated. It has been shown that the “ring effect” appearing in field emission patterns can well be explained by field emission from the peripheral regions of the field emitter. The current density distributions over the surface and in the bulk of the emitter have been analyzed     

Effects of submicrosecond, high intensity pulsed electric fields on living cells - intracellular electromanipulation

Development of technology to produce nanosecond duration pulsed electric fields has allowed examination of the effects of ultrashort duration, high intensity electric fields on living cells. Theoretically, high intensity (MV/m) electric field applications with durations of less than one microsecond, when shortened toward nanoseconds, should increasingly affect intracellular rather than surface membranes of living cells. Experimentally, square-wave, 60 ns duration, high energy (36-53 kV/cm) pulses applied in trains of 1-10 pulses result in progressive increases in the numbers of permeabilized intracellular granules in a human eosinophil cell model-without large surface membrane effects. Electron micrographic examination of cells treated in this way demonstrates alteration of intracellular granule morphology consistent with permeabilization of granule membrane, i.e., intracellular electromanipulation. Continuous microscopic examination of individual living cells exposed to long or short duration pulsed electric field applications shows that permeabilization of surface membrane (median 5 minutes) with anodic preference (electroporation) and prompt cellular swelling follow a single, long duration (100 microsecond) pulse. In contrast, after a single short duration (60 ns) pulse, onset of surface membrane permeability is delayed (median 17 minutes), the increased permeability shows no anodic preference, and cellular swelling is absent suggesting that these effects are due to intracellular electromanipulation rather than direct effects on the surface membrane. Submicrosecond, intense pulsed electric fields applied to living cells achieve preferential effects on intracellular rather than surface membranes, potentially providing new approaches for selective/generalized cell or tissue ablation, growth stimulation and tissue remodeling.     

Dielectric,ferroelectric and bipolar electric field induced strain properties of MPB composition of NBT-xKNN system

(1-x) (Na_0.5Bi_0.5TiO₃)-xK_0.5Na_0.5NbO₃/NBT-xKNN [x?=?0.07, 0.06, 0.05] ferroelectric ceramics were prepared by solid state synthesis route (SSSR). The effects of KNN contents on the microstructure, dielectric, piezoelectric and ferroelectric properties of the NBT-xKNN system were investigated in detail. For single perovskite phase formation, the calcination temperature was optimized at 800 °C for 6 h. From the XRD study, the morphotropic phase boundary (MPB) was confirmed for x?=?0.07 composition. For better densification, the sintering temperature was optimized for 1150 °C for 4 h. SEM micrographs illustrate the closely packed and non-uniform distribution of grains. Diffusive type of behaviour was observed in all the ceramics. Polarization (P) vs. electric field (E) study confirmed the ferroelectric nature of the NBT-xKNN ceramics. The bipolar field-induced strain measurement for all the ceramic samples showed butterfly-shaped loops indicating their piezoelectric nature. Among all the different compositions in MPB region, high dielectric constant (ε_r) of?~?3011, high remnant polarization (P _r ) of 17.88μC/cm² and high strain % of 0.41, were obtained in NBT-xKNN system with x?=?0.07 confirming the existence of MPB at this composition.     

An analysis of shielding against DC magnetic fields generated by electric railways. Evaluation of effective permeability of fine structure

This paper describes an effective analysis of magnetic shielding based on homogenization. The analyses become time‐consuming if the problems include the magnetic substances having fine structure. The homogenization of the structure makes it possible to analyze effectively the magnetic fields. The authors introduce a method to estimate the effective permeability of the homogenized substance. This method can be applied to any periodic structure made of magnetic substance. The magnetic shielding effects by the structures against direct‐current (DC) fields generated by electric railways are analyzed by using the present method. As a result, it is found that the overhead way and the protective fence near the railway work as a magnetic shield, whose effects can be improved by appropriate arrangement of those constructions. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 7–15, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20310     

白鹤滩坝肩边坡开挖爆破损伤预测研究

岩石高边坡开挖爆破损伤预测是爆破振动安全控制的重要基础。通过理论分析研究了岩体损伤与岩体固有频率之间的关系,提出了基于岩体固有频率变化的边坡开挖爆破损伤预测方法,基于现场爆破振动监测和声波测试开展了白鹤滩右岸坝肩边坡开挖爆破损伤预测研究。结果表明,岩体固有频率变化率与岩体损伤深度之间存在显著线性关系,边坡开挖爆破损伤预测模型随数据样本增加而动态调整并趋于稳健,白鹤滩水电站右岸坝肩边坡各梯段开挖爆破下岩体损伤深度的Bayesian LASSO预测结果低于实际观测值的概率均高于0.83,Bayesian LASSO预测结果以概率形式涵盖实际观测结果,能显示预测结果的不确定性,提出的预测方法应用效果良好。