High Frequency Electric Field Research Articles

Active and passive plasma wave investigations in the earth's environment: The cluster/whisper experiment

The Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation, WHISPER, performs high frequency electric field measurements on the four satellites of the CLUSTER mission. In active mode, the WHISPER behaves like a classical topside sounder. It provides, via the identification of resonances that are excited at characteristic frequencies of the encountered plasmas reliable and accurate determination of the total electron density and magnetic field strength. Whenever the transmitter is switched off, the WHISPER becomes a simple wave receiver (passive mode). The 2 to 80 kHz frequency range of the electric component of natural waves is then monitored. The main objective of the presentation is to highlight the plasma and natural waves diagnosis capabilities of the WHISPER instrument. The way the plasma resonances are extracted and identified is pointed out and results obtained from the solar wind down to the Earth's plasmasphere are shown.

Effect of Alignment on Transport Properties of Carbon Nanotube/Metallic Junctions

AbstractBallistic and spin coherent transport in single walled carbon nanotubes (SWCNT) are predicted to enable high sensitivity single-nanotube devices for strain and magnetic field sensing. Based upon these phenomena, electron beam lithography procedures have been developed to study the transport properties of purified HiPCO single walled carbon nanotubes for development into sensory materials for nondestructive evaluation. Purified nanotubes are dispersed in solvent suspension and then deposited on the device substrate before metallic contacts are defined and deposited through electron beam lithography. This procedure produces randomly dispersed ropes, typically 2 – 20 nm in diameter, of single walled carbon nanotubes. Transport and scanning probe microscopy studies have shown a good correlation between the junction resistance and tube density, alignment, and contact quality. In order to improve nanotubes at specific locations on the substrate surface. Lithographic techniques are used to define local areas where high frequency electric fields are to be concentrated. Application of the aligned with the electric field lines. A second electron beam lithography layer is then used to deposit metallic contacts across the aligned tubes. Experimental measurements are presented showing the increased tube alignment and improvement in the transport properties of the junctions.

Development of High Harmonic Gyrotrons Using a Permanent Magnet System

A large orbit gyrotron (LOG) operating at higher harmonics of electron cyclotron frequency has been constructed by use of a permanent magnet system whose intensity is around 1 T. The operation test was already performed successfully up to the fourth harmonic. The operation efficiency was extremely high even at the third and the fourth harmonics, because of high efficient interaction between beam electron and high frequency electric field in LOG. The test results of the LOG are summarized.

Double relaxation phenomena of monosubstituted anilines in benzene under high frequency electric field

The intercept and slope of a derived linear equation: (χoij - χij′)/χij′ = ω (τ1+τ2) χij″/χij′ - ω2τ1τ2 for different weight fractions wj's of monosubstituted anilines (j) in benzene(i) at 35°C under different electric field frequencies are used to yield the double relaxation times τ1 and τ2 of the flexible parts and the whole molecules. χij′ and χij″ are the real and imaginary parts of hf complex dielectric orientational susceptibility χij∗ and χoij is the low frequency dielectric susceptibility which is real. τj's obtained from the ratio of the individual slopes of variations of χij∥ and χij′ with wj's at wj→0 are compared with Murthy et al (Indian J Phys 63 B 1989 491) and Gopalakrishna (Trans Faradey. Soc. 53 1957 767). The theoretical weighted contributions c1 and c2 for τ1 and τ2 from Fröhlichs' equations are compared with the experimental ones from the graphically fitted curves of χij′/χoij and χij″/χoij with wj's in the limit wj=0. The values of (χij′/χoij)wj→0 and (χij″/χoij)wj→0 are again employed to get symmetric and asymmetric distribution parameters γ and δ, the latter one is from the curve of 1/ϕ log Cosϕ against ϕ0, to yield the symmetric and characteristic relaxation times τs and τcs respectively, only to show that symmetric relaxation behaviour is obeyed by the molecules. The dipole moments μ1 and μ2 for the rotation of flexible parts and the whole molecules are measured from τ1 and τ2 and linear coefficient ß's of the variations of χij′ and hf conductivity σij with wj's. The measured μ1 and μ2 are compared with the reported μ's and μtheo's of available bond angles and bond moments of the substituent polar groups of the parent molecules. The slight disagreement of measured μ's from μtheo's indicates the existence of inductive, mesomeric and electromeric effects suffered by the polar groups under hf electric field.

AC hot carrier transport in 3C- and 6H-SiC in the terahertz frequency and high lattice temperature regime

The complex mobility of electrons in 3C - and 6H-SiC subjected to intense high frequency electric fields is calculated taking into account effects of band nonparabolicity. The electric field, given by a dc component plus an ac component in the frequency range 0.1-100 THz, is applied along the [0001] ([111]) direction in the hexagonal (cubic) polytype. The real electron mobility presents a characteristic maximum peaking around 6-8 THz, while the imaginary electron mobility is structured, with characteristic minimum and maximum around 2-3 THz and 20{30 THz, respectively. These mobilities are seen to smooth down for higher temperatures in both polytypes.

Measuring Forces on Immobilized Yeast Cells

The interaction of cells with biomedical sensors or sampling systems of bioreactors is one of the most crucial problems affecting the long-term stability of such devices. Cell adhesion on sensors can be influenced by the use of different sensor materials or material coatings [1]. The cell-materialinteraction can be characterized, e.g., by the adhesion force. Additionally, filter blocking on sampling devices for large scale bioreactors can be avoided under different hydrodynamic conditions. A new approach for small volume bioreactors consists in the application of high frequency electrical fields in connection with the utilization of microsytem components in sampling systems [2]. The physical background is the so called dielectrophoretic effect, which describes forces on non-conducting but polarizable particles caused by high frequency alternating fields in the range of a few kHz to some hundreds of MHz. This dynamic effect is also detectable on microorganisms. Forces are repulsive (negative dielectrophoresis) or attractive (positive dielectrophoresis) depending on frequency, conductivity, geometric conditions of the electrode structure, but also on the complex dielectric properties of the cells (or microorganisms) and the surrounding medium [3]. The action of the dielectrophoretic force can be visualised easily by light microscopy [2], but a direct measurement of the force itself is impossible by that method. Therefore, we used the Atomic Force Microscope (AFM) as a force sensor. A necessary step in such experiments is the immobilization of cells on an AFM cantilever [4]. In our study yeast cells were immobilized on the cantilever. In one application the adhesion force of the cells was measured on different materials. Another goal of this work was the characterization of the dielectrophoretic force on immobilized cells. But an immediate measurement of the dielectrophoretic force [5] is complicated by a superimposition with electrostatic forces [6]. Nevertheless, the measured force can be splitted because of different dependencies of both forces on the AC voltage and a DC offset. As a result, a qualitative detection of the dielectrophoretic force is shown for immobilized yeast cells. A suitable method was found to immobilize yeast cells on an AFM cantilever (fig. 1). Force-distance-curves had shown a very small adhesion force of the cantilever with cells to an optical glass of type Borofloat B33 and virtually no adhesion of a blank cantilever on B33. In comparison a gold coated glas was used as a test system. We found small interactions of a blank cantilever to the gold surface, but considerable interactions in the case of the cantilever with immobilized cells. Finally, there was a larger adhesion force on a phosphorylcholine coated glass (PC 1036) in comparison to B33. On this occasion nearly equal forces appeared for blank and treated cantilevers with slight differences depending on the used cantilever type. First results were obtained to characterize the dielectrophoretic force acting on immobilized yeast cells.

Electromagnetic Induction Heating for the 70 nm Node

AbstractElectromagnetic heating provides a novel alternative to “illumination-based” rapid thermal processing techniques. Exposure to radiation, in the RF and microwave frequency regimes, rapidly heats silicon (∼125°C/sec) to temperatures in excess of 1000°C without the use of a susceptor. These ramp rates make this technology suitable for the activation of shallow implanted dopants, and satisfaction of the 100 nm technology node has been achieved. Furthermore, the presence of high frequency electric fields creates ponderomotive forces that may alter the kinetics of dopant activation and diffusion. These additional driving forces could, once fully understood, lead to an enhanced activation mechanism that activates sufficient dopants to satisfy the 70 nm technology node at temperatures less than 1000°C.

Molecular dynamics simulations of aqueous NaCl and KCl solutions: Effects of ion concentration on the single-particle, pair, and collective dynamical properties of ions and water molecules

We have performed a series of molecular dynamics simulations of aqueous NaCl and KCl solutions at different concentrations, ranging from 0 M to 4.5 M, to investigate the effects of ion concentration on the single-particle, pair, and collective dynamical properties of aqueous electrolyte solutions. The SPC/E model is used for water and the ions are modeled as charged Lennard-Jones particles. The single-particle dynamics is investigated by calculating the self-diffusion coefficients of ions and water molecules and also the orientational relaxation times. The pair dynamics is studied by evaluating the ion–water residence and water–water hydrogen bond time correlation functions. The relaxation of relative velocity autocorrelation function and the cross velocity correlation function of two hydrogen bonded water molecules are also investigated at varying ion concentration. Finally, we explore the collective dynamical properties by calculating the frequency dependent dielectric function and conductivity. It is found that the self and relative diffusion coeffcients decrease and the orientational relaxation times increase with ion concentration. The residence times of water molecules near ions and also the structural relaxation time of water–water hydrogen bonds show an increasing trend as the ion concentration is increased. The dielectric relaxation time is found to decrease with ion concentration for the solutions investigated here. The static conductivity of concentrated solutions shows significant departure from the Nernst–Einstein behavior due to formation of ion pairs. With an increase of frequency, the conductivity first increases substantially and then decreases at very high frequency. The initial increase of conductivity is attributed to the disruption of ion pairs on application of high frequency electric fields.

Dielectric relaxation phenomena of polysubstituted benzenes under high frequency electric field.

Abstract The relaxation times τ j 's and the dipole moments μ j 's in SI units of polysubstituted benzenes like meta-diisopropylbenzene, para-methylbenzoylchloride and ortho-chloroacetophenone in benzene are estimated at 30°, 35°, 40° and 45 °C from the real k ′ ij imaginary k ″ ij parts of the dimensionless complex hf dielectric constants k * ij measured under 3 cm wavelength electric field. τ j 's measured from the ratio of the slopes of the variations of imaginary σ ″ ij and real σ ′ ij parts of complex hf conductivity σ * ij with the weight fractions w j 's in the limit w j = 0 at a given temperature are reliable in comparison to the linear coefficients of variation of σ ″ ij against σ ′ ij of different w j 's (Murthy et al 1989). In the former case the polar-polar interactions are fully eliminated. The thermodynamic energy parameters with the estimated τ j 's reveal the cooperative process for p-methylbenzoylchloride unlike other two molecules besides the solute-solute and solute-solvent molecular associations. The variation of μ j 's with temperature in °C when compared to theoretical dipole moments μ theo 's from available bond angles and bond moments establishes the temperature dependence of the inductive, mesomeric and electromeric effects of the substituted polar groups of molecules.

Suppression of epileptiform activity by high frequency sinusoidal fields in rat hippocampal slices.

1. Sinusoidal high frequency (20-50 Hz) electric fields induced across rat hippocampal slices were found to suppress zero-Ca2+, low-Ca2+, picrotoxin, and high-K+ epileptiform activity for the duration of the stimulus and for up to several minutes following the stimulus. 2. Suppression of spontaneous activity by high frequency stimulation was found to be frequency (< 500 Hz) but not orientation or waveform dependent. 3. Potassium-sensitive microelectrodes showed that block of epileptiform activity was always coincident with a stimulus-induced rise in extracellular potassium concentration during stimulation. Post-stimulus inhibition was always associated with a decrease in extracellular potassium activity below baseline levels. 4. Intracellular recordings and optical imaging with voltage-sensitive dyes showed that during suppression neurons were depolarized yet did not fire action potentials. 5. Direct injection of sinusoidal current into individual pyramidal cells did not result in a tonic depolarization. Injection of large direct current (DC) depolarized neurons and suppressed action potential generation. 6. These findings suggest that high frequency stimulation suppresses epileptiform activity by inducing potassium efflux and depolarization block.

Dielectric relaxation phenomena and high frequency conductivity of rigid polar liquids in different solvents

Abstract The double relaxation phenomena in apparently rigid aliphatic polar liquids (j) like chloral and ethyltrichloroacetate in nonpolar solvents (i) benzene, n-hexane and n-heptane under 4.2, 9.8 and 24.6 GHz electric fields at 30°C have been studied. Only five systems of polar-nonpolar liquid mixtures show the double relaxation times τ 1 and τ 2 due to rotation of their flexible parts and the whole molecules. The probability of showing the double relaxation phenomena is greater in aliphatic solvents at 9.8 and 24.6 GHz electric fields indicating their nonrigidity. This is also supported by the symmetric and asymmetric distribution parameters γ and δ estimated from values of x and y at w j → 0 involved with dimensionless dielectric constants k′ ij , k″ ij , k oij and k ∞ij of solutions. The variation of x and y with weight fractions w j 's of solutes are found to be unusual predicting their probable solute-solvent and solute-solute molecular association under high frequency (hf) electric fields. The dipole moments μ 1 and μ 2 of the flexible parts and the whole molecules from the slopes β's of hf conductivities σ ij ' s with w j 's and the estimated τ 1 and τ 2 reveal their solute-solute associations in the aliphatic solvents. The theoretical dipole moments μ theo 's in terms of available bond angles and bond moments conform the estimated μ j 's only to establish the existence of mesomeric, inductive and electromeric effects in them.

Dielectric relaxation of para polar liquids under high frequency electric field

Abstract The structural and associational aspects of nonspherical para polar liquids (j) in nonpolar solvents (i) are studied through high frequency conductivities σij's of solutions. The relaxation time τ of the respective liquids under 3cm. wavelength electric field at various experimental temperatures in °C are estimated from the slope of individual variations of real σ′ij and imaginary σ″ij parts of hf complex conductivity σ ∗ ij with weight fractions wj's of polar liquid. The temperature variation of τ for comparatively larger nonspherical para molecules in dioxane are not strictly obeyed by the Debye model unlike other simpler para di- or tri-substituted benzene in benzene. Thermodynamic energy parameters ΔHτ, ΔSτ and ΔFτ are obtained from Eyring's rate process equation with the estimated τ's in order to get information on the solvent environment around them. The higher values of γ obtained from lnτjT against lnη equation indicate the solid phase rotators for the liquids. The estimated Kalman and Debye factors τjT/ηγ and τjT/η establish the Debye relaxation mechanism for almost all the para-molecules. The obtained dipole moments μj's in terms of slope β of σij-wj curve and dimensionless parameter ‘b’ involved with estimated τ are then compared with the reported μ and μtheo obtained from bond angles and bond moments. The μj's of para liquids are often zero but at other temperatures they show net moments. The slight disagreement between the measured and theoretical μ's reveals the presence of the inductive and mesomeric moments of substituted polar groups in molecules at different temperatures.

Characterization of deep impurities in semiconductors by terahertz tunneling ionization

Tunneling ionization in high frequency fields as well as in static fields is suggested as a method for the characterization of deep impurities in semiconductors. It is shown that an analysis of the field and temperature dependences of the ionization probability allows to obtain defect parameters like the charge of the impurity, tunneling times, the Huang–Rhys parameter, the difference between optical and thermal binding energy, and the basic structure of the defect adiabatic potentials. Compared to static fields, high frequency electric fields in the terahertz-range offer various advantages, as they can be applied contactlessly and homogeneously even to bulk samples using the intense radiation of a high power pulsed far-infrared laser. Furthermore, impurity ionization with terahertz radiation can be detected as photoconductive signal with a very high sensitivity in a wide range of electric field strengths.

Expansion of polystyrene using water as the blowing agent

Heating of polystyrene beads containing pentane isomers as the blowing agent traditionally produces polystyrene foam. Undesirable emissions of the blowing agent and its high flammability are the complications of this process. A new process for the production of expandable polystyrene has been developed, using water as the blowing agent. Water is trapped inside the polystyrene matrix through the use of starch that is introduced as a separate phase during the suspension polymerization. The problems created by the incompatibility of starch with the organic phase can be partially overcome by “compatibilization” with maleic anhydride. The type of starch can influence the foam morphology of the pre-expanded beads, while the density is changed only in the range of the experimental error. The density of the pre-expanded beads is influenced by the blowing technique used (hot air or high frequency electric field). The use of these different blowing techniques does not influence significantly the foam morphology.

GMRES Computation of High Frequency Electrical Field Propagation in Land Mine Detection

The ultimate goal of the authors is to apply inverse problem techniques to image land mines using an electromagnetic signal originated by ground penetrating radar. Specifically, the intention is to use the recently developed elliptic systems method, which has been successfully applied by these authors to the problem of imaging biological tissues using lasers. As the first step it is necessary to develop a fast and accurate numerical method for the solution of the forward problem to simulate data for the inverse problem. The main challenge is the requirement of solving a Helmholtz-like equation for high frequencies which is excessively time consuming using standard direct solution techniques. A novel accurate and rapid numerical procedure for the solution of this equation is described in this paper. The kernel of this algorithm is a combination of GMRES and a carefully chosen preconditioner, the solution of which is found using a fast transform method. The extended problem of solving Helmholtz-like equations for many frequencies is also considered. Numerical results for realistic ranges of parameters in soil and mine-like targets, the investigation of the impact of the size of the truncation region on accuracy, and the sensitivity of detector readings to changes in the media are presented.

アモルファスセラミック圧粉体のミリ波焼結

The methodology of multi-variables control in millimeter wave sintering is set up, in order to provide a route to the design and development on advanced materials of next generation such as bulk nanocrystalline ceramics. The 28 GHz microwave sintering system has an intelligent peripheral equipment with a specially designed displacement sensor necessary for the real-time measurement and the closed loop control of a linear shrinkage. The CIP'ed compact of amorphous ZrO2-20mol%A12O3 powder, as synthesized via mechanical alloying, can be sintered to a full density without any macroscopic crack by employing millimeter wave heating followed by holding at a relatively low temperature of 1523 K. The rapid densification of the nanocrystalline ZrO2-20mol%Al2O3 compact in heating under a high frequency electric field is fairly well expressed by an Arrhenius relation ofe=Aexp (-H/kT) with an apparent activation energy (H) of 198 kJmol-1. Furthremore, the apparent activation energy tends to increase with increasing relative density in the case of a constant densification rate control sintering.

Single micro electrode dielectrophoretic tweezers for manipulation of suspended cells and particles

Cells or particles in aqueous suspension close to a single capacitively coupled micro electrode (CCME) driven with high frequency electric fields experience dielectrophoretic forces. The effects near the CCME can be used for trapping and manipulation of single cells using externally metallised glass pipettes and might be used to develop a microscope based on force or capacitance measurements in conductive media.

Conditions for coherent vibrations in the cytoskeleton

Mechanism of organization and order in biological systems is not satisfactorily explained yet. Biophysical theories predicted that coherent endogenous electric field of high frequency can play a significant role in organization. The polarity of vibration structures, spectral energy transfer caused by nonlinearities, and energy supply can lead to energy condensation and excitation of coherent states. These conditions are satisfied in the polymer structures of the cytoskeleton, in particular, in the microtubules as follows from experimental findings. Nonetheless, experimental verification of energy condensation and coherent vibrations in the cytoskeleton is still missing.

Space charge field enhancement in photorefractive materials by high frequency applied electric fields: analytical studies of resonances and enhancement by step-like wave forms

Analytical solutions are presented for the ionized donor density (related in a simple manner to the space charge field) when a high frequency electric field is applied to the photorefractive material. An approximate solution for an arbitrary profile of the applied field is found by generalizing the averaging technique of Stepanov and Petrov. An alternative approach for step-like wave forms is also presented. Examples are provided for three special cases when the periodic variation of applied electric field is in the form of a square wave, a symmetric pulse or an asymmetric pulse. Resonance conditions are discussed, and resonance curves are presented for the asymmetric pulse. For the symmetric pulse it is shown that the trap density limitations cannot be overcome.

Influence of a periodic field on the distant electron transfer in biological systems

Generalization of the Marcus transfer rate is derived for the case of a dissipative long-range donor–acceptor electron transfer (ET) mediated by specific bridging electron pathways in biological systems and driven by ac-electric field. High-frequency electric field is shown to block and even to invert the transfer if a specific relation between amplitude and frequency of the ac-field is fulfilled.