High Frequency Electric Field Research Articles

Mass transport in ionic crystals induced by the ponderomotive action of a high-frequency electric field.

A possible explanation of the experimentally observed enhancement of mass transport processes in ionic crystalline solids under the action of high-frequency (HF) electromagnetic fields is suggested. It is based on the ponderomotive effects that occur due to the nonlinear interaction of the HF electric field with the space charge induced by it within the crystal near its surface. Due to the action of the tangential component of the field in the near-surface amorphized layer, where the vacancy mobility is greater than in the bulk, the ponderomotive effects are found to be of sufficient strength to manifest themselves in the experimental conditions.

Spiral waves in liquid crystal

We report experimental investigation and theoretical interpretation of the formation of sprial waves in a nematic liquid crystal subjected to a rotating magnetic field and a high frequency electrical field.

Behavior of Diffusion on Flames in AC Electric Field and DC Magnetic Field. Electrical Mobility of Soot Particle in AC Electric Field and Flame Deformation in DC Magnetic Field.

A diffusion flame at a low flow rate of propane gas in still air was surrounded by a circular mesh electrode. A circular burner of 8 mm diameter was used as the other electrode. Alternating electric field of high frequency and high voltage was applied between these electrodes. The luminosity which radiated from high temperature soot particles was measured by a photomultiplier. The oscillating frequency of the luminosity changed proportionally up to 80 Hz with the frequency of the applied electric field. The electrical mobility and effective equivalence diameter of soot particles in the flame were estimated by means of the displacement of the luminous signal and the relaxation time of the soot particles. Average values were calculated to be about 0.15 m2/(V·s) and 40 μm respectively. The deformation of diffusion flames at low flow rate has been investigated numerically by the use of a rectangular nozzle in magnetic field. The deformation of the flame was independent of the direction of the magnetic field. The strength of the external force by the magnetic field was proportional to the value of two powers of magnetic field (=H2) . The force exerted upon the boundary between the flame and the air by the magnetic field was one induced by the difference of the volumetric susceptibility between the two gases. The deformation, tilt and turn of the flame are caused by the buoyancy and the induced force by the magnetic field. The numerical analysis of the turn of the flame was conducted using the value of the pressure difference at the boundary between the two gases.

Mass Transport and DC Electromotive Force Induced in Ionic Crystals by High-Frequency Electric Field

AbstractResults of the theoretical study of the effects produced on ionic crystals by highfrequency electric fields of moderate intensity are presented. The ponderomotive action of the electric field on the space charge induced by it in a thin layer within the crystal near its surface causes directional mass transport that leads to plastic deformation and induces a stationary distribution of electric potential. The analysis shows that the proposed effect (that appears to be equivalent to the action of mechanical stresses which exceed the electromagnetic pressure by many orders of magnitude) can influence the results of processing of ionic crystalline materials significantly.

Determination of aging-model constants under high frequency and high electric fields

Polypropylene film is tested for life under HV, frequencies up to 30 kHz, and aging and breakdown studies are conducted. The life data obtained is applied to three different aging models relating electric stress to time to failure: the inverse power, the exponential and the thermodynamic model. The dependency of the constants of these models on the frequency of the applied voltage is determined. The results show that the aging model constants are dependent on applied voltage and frequency. >

Suppression of the alpha particle driven Alfven instability by lower hybrid waves

The effect of quasi-linear diffusion of alpha particles in an external high frequency (HF) field on the continuum Alfven wave instability driven by the pressure gradient of the alpha particles is investigated theoretically in the limit of weak 'collisions' (νQL < ϵωA < ωbα), where νQL, ϵ = r/R, ωA and ωbα are the characteristic frequency of the quasi-linear process, inverse aspect ratio of the tokamak, Alfven frequency and alpha particle bounce frequency, respectively. It is shown that in this limit efficient instability suppression is possible. The HF electric field strength needed for stabilization is available from modem HF power sources

Comparison of microwave and r.f. plasmas: fundamentals and applications

It is now generally accepted that the frequency ω/2π at which a high frequency (HF) discharge is excited has considerable influence on the properties of the plasma. For example, the electron density n obtained for a given HF power density ¢PA in the plasma is usually higher at microwave (MW) than at radio frequencies. This, in turn, strongly affects the outcome of a given plasma process, for example etching or deposition. The analysis which has been developed to account for this calls on the dependence of the electron energy distribution function (EEDF) upon ω. This paper is divided into three main parts. In a first section, following a brief introduction, we review recent work on the kinetic modelling of low pressure HF discharges, which is based on the determination of the EEDF from the Boltzmann equation for electrons under the action of the HF electric field. This allows us to calculate the parameters which can be compared with experimental data, for example the mean power θ absorbed by an electron from the HF field. The second section reviews a series of experiments in these laboratories which have been specifically designed to investigate the influence of ω on plasma processing of materials, namely plasma etching of a polymer (polyimide), and deposition of thin plasma polymer films. 3inally, in the third section we briefly review our recent research on ion bombardment effects in dual frequency (MW-r.f.) plasmas, where the beneficial effects of MW excitation and r.f.-induced bias voltage act to enhance synergistically plasma processes.

Small signal a.c. response of hot electrons in n-Hg 0.8Cd 0.2Te in the extreme quantum limit at low temperatures

The small signal a.c. response of hot electrons in narrow band gap semiconductors to a high frequency electric field in the presence of a quantizing magnetic field has been investigated using the displaced Maxwellian approach. The model includes the non-equipartition of phonons. Landau level broadening due to electron impurity scattering and electron confinement in the extreme quantum limit at low temperatures. The energy loss rate is determined by inelastic acoustic phonon scattering via deformation potential and piezoelectric coupling while the momentum loss rate is taken to be due to acoustic phonon, ionized impurity and alloy disorder scattering. The effects of band nonparabolicity and screening on the normalized mobility have been investigated. The effect of alloy scattering in a narrow-gap alloy semiconductor such as Hg x Cd 1− x Te on the a.c. mobility has also been analysed.

NONLINEAR TRANSPORT OF ELECTRONS UNDER A STRONG HIGH FREQUENCY ELECTRIC FIELD IN SEMICONDUCTORS

The nonlinear transport of electrons in semiconductors is studied when a strong high frequency (HF) electric field is applied together with a direct current (dc) electric field. A set of equations is developed, from which the amplitude and phase of each harmonic component of the electron drift velocity and the electron temperature can be computed. In the weak HF field limit our approach reduces to the well-known memory function method. The DC conductivity decreases and definitely becomes negative with increase of the first and second harmonic components of the applied HF field. Comparison is made with experiment.

Theory of the breakdown of porous dielectrics with a high frequency electric field

The theory of the breakdown of porous dielectrics with a high frequency alternating electric field has been outlined and the dependence of the breakdown field on its frequency has been noted. A comparison of the dependence's theoretical value with the experimental data has been made and a good deal of agreement has been found between experimental data and the theory.

The force of mutual cell attraction induced by radio frequency electric fields

The mutual approach of pea protoplasts induced by high frequency electric fields (1 to 11.5 MHz) was measured as a function of time. The force of attraction was calculated from the rates of cell approach. It varied from about 10 −14 N for separation of 3 cell diameters to about 10 −12 N for separation of 1 μm at field strength 36 V/cm and solution conductivity 0.24 mS/cm. The force decreased with increasing conductivity but was not sensitive to frequency variations in the 1 to 11.5 MHz range. The numerical calculation based on the exact solution of the Laplace equation for two conducting spheres in dielectric medium gave a functional dependence similar to the experimental observation, but yielded higher values for the force. These first quantitative measurements of intercellular force induced by radio-frequency electric fields indicate that attraction depends strongly on separation and medium conductivity, but not significantly on frequency. These findings may help in understanding mechanisms of interactions of cells with electric fields, cell electrofusion and electrocoagulation.

The force of mutual cell attraction induced by radio frequency electric fields

The mutual approach of pea protoplasts induced by high frequency electric fields (1 to 11.5 MHz) was measured as a function of time. The force of attraction was calculated from the rates of cell approach. It varied from about 10 −14 N for separation of 3 cell diameters to about 10 −12 N for separation of 1 μm at field strength 36 V/cm and solution conductivity 0.24 mS/cm. The force decreased with increasing conductivity but was not sensitive to frequency variations in the 1 to 11.5 MHz range. The numerical calculation based on the exact solution of the Laplace equation for two conducting spheres in dielectric medium gave a functional dependence similar to the experimental observation, but yielded higher values for the force. These first quantitative measurements of intercellular force induced by radio-frequency electric fields indicate that attraction depends strongly on separation and medium conductivity, but not significantly on frequency. These findings may help in understanding mechanims of interactions of cells with electric fields, cell electrofusion and electrocoagulation.

The behavior of ion pairs in high frequency electric fields exemplified by acetonitrile solutions of Bu4NBr

Permittivity data from 0.9 to 40 GHz for acetonitrile and 0.05 to 1.4 molar acetonitrile solutions of Bu4NBr at 25°C are used to exemplify the behavior of ion pairs in high frequency electric fields. Measurements were excuted by the method of travelling waves with equipment known to produce data of high precision. Data analysis of the acetonitrile spectrum shows a single relaxation process at relaxation time of 3.5 ps for the solvent reorientation; the spectra of the salt solutions reveal two relaxation processes with relaxation times increasing from 3.5 to 6.8 ps for the solvent and decreasing from 120 to 70 ps for the ion pair [Bu4NBr]o at increasing salt concentration. The association constant of Bu4NBr in acetonitrile determined by permittivity measurements agrees well with that from conductance measurements. The concentration-dependence of the ion-pair relaxation times reveals the rate constants of ion-pair formation and decomposition.

On stabilization of mirror isomers in a high frequency electric field

Abstract A possible origin of life on earth due to the stabilization of mirror L- and D-isomers by a hf electric field is analytically suggested. The frequency of the field should satisfy the inequality ω ⪢ k where k is the rate of chemical transformation L D. It is emphasized that the external outer oscillating field may control the transition rate depending on its frequency ω. It can result either in stabilization of isomers in one state or in increase of the rate of L-D transition.

Local deformation of human red blood cells in high frequency electric field

A method of local and general deformantion of single erythrocytes by external forces in high-frequency electric field is described. The method allows the avoidance of any mechanical contact of the cell with electrodes. Under the action of the forces applied human erythrocytes change their shape and produce various membrane structures: long filopodia-like processes, retraction fibers and lamella-like structures. These structures are never formed by erythrocytes under normal conditions, but are typical for fibroblasts, macrophages and epithelium cells. By the method developed the elastic properties of spicules on the membranes of echinocytes were also studied. Deformation of echinocyte in high-frequency electric field leads to the smoothing out of spicules. However, after the electric field is turned off, echinocyte restores its initial forms including the number and localization of all initial spicules on the cell surface.

Optical Radiation Efficiency of Surface-Wave-Produced Plasmas as Compared to DC Positive Columns

The influence of the high-frequency (HF) field (200-900 MHz), gas pressure (0.05–1.0 Torr) and plasma density on the radial density distribution of excited atoms in a cylindrical HF sustained discharge of the surface-wave type is experimentally examined through optical emission spectroscopy, with the use of a tomography technique. These results illustrate the role of the radial inhomogeneity of the wave electric field intensity (the so-called skin effect) on the radial density distributions of excited atoms. This set of data, completed by similar measurements for the positive column of a dc discharge, is further used to investigate the optical radiation efficiency as a function of the field frequency. It shows that there exist discharge conditions for which the surface-wave plasma is more efficient, the optimum frequency then being around 200 MHz. The explanation for such a behavior calls on the frequency dependence of both the radial density distribution of the excited atoms and the electron energy distribution function (EEDF), the latter determining how the power absorbed from the HF electric field is shared between ionization and excitation processes. These various results are compared with the self-consistent model developed for surface-wave discharges in argon by Ferreira and co-workers.

Application of high frequency electric fields to the reduction of ferric oxide: V L Shvartzman, Poroskovaya Metallurgia, No 3, 1990, 1–4. In Russian

Application of high frequency electric fields to the reduction of ferric oxide: V L Shvartzman, Poroskovaya Metallurgia, No 3, 1990, 1–4. In Russian

On the theory of control of chemical reactions by oscillating high frequency electric field

An explicit analytical prove is given of the fact that the rate of chemical reaction can be controlled by an external oscillating high frequency electric field under the condition that its frequency is ω = 2 Q/ħn when n is an even integer, and Q a reaction heat. We managed to carry out computations and obtained the result based upon the relationship: chemical reaction—two-level system. As for the electric field it has been taken into account via introduction into the Hamiltonian of the additive of the type V̂ =— d̂·E , where d̂ is the operator of the dipole momentum of the reacting atoms, E is the strength of the electric field.

Microwave breakdown voltages in hydrogen from DC data

The general microwave breakdown characteristic in hydrogen is obtained from the DC dependence of the ionization coefficient and electron mean energy on the reduced electric field, using the basic equations of motion of electrons in a high frequency electric field. Excellent agreement is obtained between the calculated characteristic and experimental values from the literature. With the aid of the derived effective reduced electric field concept, specific breakdown characteristics are then obtained for given microwave cavities. These also agree well with experimental results except well below the Paschen minimum, confirming the validity of the concept. The subject is presented as a self-contained entity and its analogy with an applied crossed magnetic field is emphasized. A direct comparison between the microwave and the DC Paschen formula is made.

Interactions of Electromagnetic Radiation with Electrolytes at High to Ultra-High Frequencies

Abstract At frequencies above one megahertz, the behaviour of electrolytic solutions changes from an ionic conductor to a lossy dielectric. High frequency conductance measurements of aqueous electrolytes (Na2SO4 and KCl) have been made by continuous wave and pulse admittance methods, in cells with immersed, shiny Pt electrodes to study this transition. Peak conductance frequencies as a function of concentration did not conform to the classical circuit representation of a resistance and capacitance. Measured phase angles indicate that relatively concentrated electrolytes (0.001 − 1 M) exhibit inductance due to electromagnetic and perhaps mass (inertial) effects. Modelling was possible with a constant value of the inductance, L, and capacitance, C, using a simple RLC equivalent circuit. Ion and solvent perturbations in high frequency electrical fields first are discussed in terms of a damped harmonic oscillator model, whose macroscopic response is self-consistent and equivalent mathematically to RLC network...