High Frequency Electric Field Research Articles

Microchamp sur un traceur

Mixtures of two ionic species are simulated by classical molecular dynamics, where a screened potential accounts for the high frequency electric field from free electrons. With an absolute precision of 1% of the maximum, the resulting probability distribution of the quasi static microfield at ions or neutrals is characterized by a simple rational fraction involving only three parameters, which are given for a wide variety of charges and concentrations.

Development of an Optoelectrostatic Micropump Using a Focused Laser Beam in a High-Frequency Electric Field

In this paper, fluid flow generated by laser irradiation in a high-frequency electric field was investigated with a view to using it as the driving force for a micropump. We discovered an optoelectrostatic phenomenon known as optoelectrostatic microvortex (OEMV) ten years ago. The OEMV is generated around the focal point of a laser beam located in the center of an intense high-frequency electric field. The direction of the opposed flow is parallel to the ac electric field and perpendicular to the sides of the electrodes. In this paper, the laser focus was positioned near one of the electrodes. One-directional flow was generated toward the other electrode. This flow was generated in a microchannel by simultaneous application of an Nd:YAG laser (1064 nm) and an ac voltage. The flow velocity increased with both increasing laser power and increasing ac voltage. In addition, the flow velocity was affected by the ac frequency. The flow velocity around the focal point was several hundred micrometers per second. At a distance of 3 mm from the laser spot, a flow velocity of 25 mum/s (0.74 muL/s) was observed

High-frequency electric field amplification in a magnetized plasma

In the investigation of cyclotron ion heating in systems designed for plasma isotope separation, the high-frequency (HF) electric field amplification effect was found to occur in equilibrium plasma. In the present article this effect is treated as a result of the interaction of the plasma placed in a constant external magnetic field with the HF modes of the vacuum chamber. Consistent elaboration of this approach allowed obtaining a clear interpretation of the HF electric field amplification effect and constructing a simple model of HF field excitation in a plasma column embedded in the external magnetic field.

Structured waves near the plasma frequency observed in three auroral rocket flights

Abstract. We present observations of waves at and just above the plasma frequency (fpe) from three high frequency electric field experiments on three recent rockets launched to altitudes of 300–900 km in active aurora. The predominant observed HF waves just above fpe are narrowband, short-lived emissions with amplitudes ranging from <1 mV/m to 20 mV/m, often associated with structured electron density. The nature of these HF waves, as determined from frequency-time spectrograms, is highly variable: in some cases, the frequency decreases monotonically with time as in the "HF-chirps" previously reported (McAdams and LaBelle, 1999), but in other cases rising frequencies are observed, or features which alternately rise and fall in frequency. They exhibit two timescales of amplitude variation: a short timescale, typically 50–100 ms, associated with individual discrete features, and a longer timescale associated with the general decrease in the amplitudes of the emissions as the rocket moves away from where the condition f~fpe holds. The latter timescale ranges from 0.6 to 6.0 s, corresponding to distances of 2–7 km, assuming the phenomenon to be stationary and using the rocket velocity to convert time to distance.

Material properties of dipolar liquid in non-polar solvent through relaxation phenomena under high frequency electric field

A graphical method is used to determine the double relaxation times τ 2 and τ 1 for the rotation of the flexible part and the whole molecule of some long-chain alcohols in n-heptane under 24.33 GHz (K-Band), 9.25 GHz (X-Band) and 3.00 GHz (J-Band) electric fields on the basis of Debye and Fröhlich models. The fixed τ 1 and τ 2 at those frequencies are compared to the average τ 1 and τ 2 measured by the single frequency method of Saha et al. [U. Saha, S.K. Sit, R.C. Basak, S. Acharyya. J. Phys. D: Appl. Phys. 27 (1994) 596.] and reported average τ's. This reveals the material properties of the chemical systems in identical environments. τ's thus obtained agree well with the reported average τ's at three different frequencies for most of the alcohols. This at once indicates the whole molecular rotation of the dipolar molecules at those frequencies. The dipole moments μ 1 and μ 2 are, however, measured from the linear coefficients β of hf susceptibilities χ ij′ curves against weight fractions w j of the alcohols at all the frequencies in terms of the graphically obtained τ 1 and τ 2 and the reported τ by the existing methods. Theoretical dipole moments μ theo from the available bond angles and bond moments are also determined. The slight disagreement among the μ theo, reported and estimated μ indicates the existence of the inductive, electromeric and mesomeric effects of the substituent polar group –OH attached to the parent ones.

Experimental study on the deformation of erythrocytes under optically trapping and stretching

The mechanical behavior of erythrocytes is studied experimentally and numerically. In the experiment, prepared silica microbeads are attached to the surface of spherically swollen erythrocytes (red blood cells, RBCs) at room temperature (25 °C). The cells are then stretched by single laser beam via the microbeads. The relation of deformation and stretching force is quantitatively assessed by the image processing of digital pictures. Meanwhile, a physical model for an axisymmetric cell is introduced to study its deformation by different level of stretching force. By comparing the experimental and numerical data, stiffness of the cell membrane can be determined and the optimal values are found to agree with other studies by different techniques such as micropipette aspiration or high frequency electric field.

Manipulation of single-wall carbon nanotubes into dispersively aligned arrays between metal electrodes

A dispersively aligned carbon nanotube array has been achieved between metal electrodes by electric-field assisted manipulation of surface modified single-wall carbon nanotubes (SWCNTs). Surface modification of SWCNTs with octadecylamine (ODA) molecules creates well-dispersed SWCNT solutions and effectively obviates the entanglement between deposited SWCNTs. The alignment effect of SWCNTs is improved by aligning them with an ac electric field of high frequency in a high-volatility solvent. The good electrical contact between the aligned SWCNTs and the metal electrodes is obtained by adopting a UV-light radiation method for removing the grafted ODA on the aligned SWCNTs.

Differences in success of repeat ablation procedure for recurrent atrial fibrillation after two different ablation strategies: Results from a prospective randomized study comparing pulmonary vein isolation versus circumferential pulmonary vein ablation

Minnesota.) non-fluoroscopic mapping system has the potential to reduce X-ray exposure during electrophysiological procedures. This is the first prospective randomised controlled study to compare radiation exposure, safety and cost between conventional, electroanatomical (Carto) and high frequency electrical field (NavX) mapping techniques. Methods: All patients undergoing catheter ablation (except AV node and AF ablation) were randomised to a Carto, NavX or conventional mapping procedures. Immediate procedural success was defined using standard criteria (eg bi-directional block for typical atrial flutter, non inducibilty of AVNRT/AVRT etc). All patients were seen 6 weeks following the procedure and success defined as both freedom from symptoms and no documented recurrence of any arrhythmia other than ectopy. Procedure costs included diagnostic and ablation catheters, Carto reference patch and the complete NavX kit. All costs are the published UK list prices. Statistical comparison was made against conventional procedures. Results: Eighty-nine patients (54% men) aged 48 17 (mean SD) were randomised. 5 patients were withdrawn as no arrhythmia could be induced. There were no significant differences between Carto and NavX in any variable. Conclusion: For all catheter ablation procedures, procedure duration and outcome are similar for Carto, Navx and conventional procedures. Both Carto and NavX are associated with reduced fluoroscopy time and radiation dose compared to conventional x-rays but at an increased cost. The costs of NavX are likely to reduce as we become more comfortable using fewer catheters for EP procedures.

Catheter location trial: A prospective randomised comparison of Carto, NavX and conventional for catheter ablation

Introduction: The EnSite NavX (Endocardial Solutions, Inc. St Paul, Minnesota.) non-fluoroscopic mapping system has the potential to reduce X-ray exposure during electrophysiological procedures. This is the first prospective randomised controlled study to compare radiation exposure, safety and cost between conventional, electroanatomical (Carto) and high frequency electrical field (NavX) mapping techniques.

FROM BLOCH MODEL TO THE RATE EQUATIONS II: THE CASE OF ALMOST DEGENERATE ENERGY LEVELS

Bloch equations give a quantum description of the coupling between atoms and a driving electric force. It is commonly used in optics to describe the interaction of a laser beam with a sample of atoms. In this paper, we address the asymptotics of these equations for a high frequency electric field, in a weak coupling regime. The electric forcing is taken quasiperiodic in time.We prove the convergence towards a rate equation, i.e. a linear Boltzmann equation, recovering in this way the physically relevant asymptotic model. It describes the transitions amongst the various energy levels of the atoms, governed by the resonances between the electric forcing and the atoms' eigenfrequencies. We also give the explicit value for the transition rates.The present task has already been addressed in Ref. 5 in the case when the energy levels are fixed, and for different classes of electric fields. Here, we extend the study in two directions. First, we consider almost degenerate energy levels, a natural situation in practice. In this case, almost resonances might occur. Technically, this implies that the small divisor estimates needed in Ref. 5 are false, due to the fact that the Diophantine condition is unstable with respect to small perturbations. We use an appropriate ultraviolet cutoff to restore the analysis and to sort out the asymptotically relevant frequencies. Second, since the asymptotic rate equation may be singular in time, we completely analyze the initial time-layer, as well as the associated convergence towards an equilibrium state.

First 100 ms of HF modification at Tromsø, Norway

Experiments were performed with the high‐power, high‐frequency (HF) facility at Tromsø, Norway to test theoretical predictions for the excitation of ion and Langmuir oscillations in the ionosphere. The principal diagnostic of wave‐plasma interactions was the VHF radar at the European Incoherent Scatter (EISCAT) facility. This radar is collocated with the HF facility. High‐resolution radar techniques were used to monitor the temporal development of the ion and Langmuir oscillations. HF pulses 100 ms in duration were periodically transmitted into a smooth background F region plasma. Measurements of the radar backscatter spectra show that all key spectral features predicted by strong Langmuir turbulence theory are simultaneously present in the plasma and that their evolution is in agreement with theoretical expectations. However, several new features have been observed that are not anticipated by current theory. The experimental results reinforce the notion that new theoretical developments are needed to accommodate the large HF electric fields produced at Tromsø and treat the electron acceleration process in a self‐consistent fashion.

Dynamic characteristics of non-ideal plasmas in an external high frequency electric field

The dynamic electric conductivity, dielectric permeability and refraction and reflection coefficients of a completely ionized gaseous plasma in a high frequency (HF) external electric field are calculated. These results are obtained within the self-consistent field approach developed earlier for the static conductivity determination. The plasma electron density, Ne, and temperature, T, varied within the following limits: 1019 ≤ Ne ≤ 1021 cm−3 and 2 × 104 ≤ T ≤ 106 K, respectively. The external electric field frequency, f, varied in the range 3 GHz≤ f ≤ 0.05ωp, where ωp is the circular plasma frequency. Thus, the upper limit for f is either in the microwave or in the far infrared frequency band. The final results are shown in a parameterized form, suitable for laboratory applications.

A Periodic Director Structure of Nematic Liquid Crystals in a High-Frequency Electric Field

We report an electrohydrodynamic instability, the prewavy instability, in nematic liquid crystals in a high-frequency electric field. This instability shows isotropic feature, zigzag flows, and constant spatial periodicity with respect to the amplitude and frequency of the applied electric field. It should be distinguished from similar instabilities such as the isotropic electrolyte mode, the inertia mode and the dielectric mode reported already.

Wide Viewing Angle and Fast Responding TN LCD

A new type of TN display device has been fabricated by sandwiching a dual frequency addressable nematic liquid crystal material between two unrubbed polyimide coated glass plates. Between crossed polarizers, the bright state is observed by applying a high frequency electric field, while the dark state by applying a low frequency electric field of similar strength. This dual frequency addressed rubbing free device shows very wide and highly symmetric viewing angle characteristics, with contrast ratio comparable to that of a rubbed TN device, and with very fast response time. Addressing the device in a “dual frequency dual amplitude pulsed mode” leads to only a small increase (∼1.5 times) in power consumption in comparison with the conventional single frequency addressed device.

Force-extension curve of a polymer in a high-frequency electric field.

We study theoretically the conformation and force-extension curve of a semiflexible polymer in a spatially uniform ac electric field. The polymer backbone minimizes its energy by aligning along one of two orientations parallel to the field. In a strong ac field, hairpin kinks develop between regions of opposite alignment. These kinks are mathematically described as sine-Gordon solitons. We calculate the equation of state of the one-dimensional kink gas, which yields the force-extension curve of the polymer. A sufficiently strong ac field causes the polymer to extend spontaneously to almost its full contour length. The theory is applied to recent experiments on dielectrophoretic stretching of DNA.

Influence of electric field type on the assembly of single walled carbon nanotubes

Electric field assisted assembly of single walled carbon nanotubes (SWCNTs) on lithographically patterned electrodes has been studied using both dc and ac electric fields. The nanotube alignment is strongly dependent on the magnitude and the frequency of the applied electric field. An improved carbon nanotube (CNT) orientation is achieved with ac electric field of high frequency due to alternating force exerted rapidly on field-induced dipoles of the nanotubes and the nanotubes orient nearly at right angle to the metal electrodes. The purification of as-prepared CNTs from background nanoparticles appears possible by aligning nanotubes with an ac electric field.

Relaxation phenomena of polar non-polar liquid mixtures under low and high frequency electric field

Simultaneous calculation of the dipole moment μj and the relaxation time τj of a certain number of non-spherical rigid aliphatic polar liquid molecules (j) in non-polar solvents (i) under 9.8 GHz electric field is possible from real e′ij and imaginary e″ij parts of the complex relative permittivity e*ij. The low frequency and infinite frequency permittivities e0ij and e∞ij measured by Purohitet al [1,2] and Srivastava and Srivastava [3] at 25, 35 and 30°C respectively are used to obtain static μs. The ratio of the individual slopes of imaginary σ″ij and real σ′ij parts of high frequency (hf) complex conductivity σ*ij with weight fractionsw jatw j → 0 and the slopes of σ″ij— σ′ij curves for differentw js [4] are employed to obtain τjs. The former method is better in comparison to the existing one as it eliminates polar-polar interaction. The hf μjs in Coulomb metre (C m) when compared with static and reported μs indicate that μs s favour the monomer formations which combine to form dimers in the hf electric field. The comparison among μs shows that a part of the molecule is rotating under X-band electric field [5]. The theoretical μtheos from available bond angles and bond moments of the substituent polar groups attached to the parent molecules differ from the measured μjs and μs to establish the possible existence of mesomeric, inductive and electromeric effects in polar liquid molecules.

Transport dielectrophoretique de microgouttes pour un lab-on-chip a vocation biologique

Click to increase image sizeClick to decrease image sizeThis work concerns the design of microsystems for the travelling of liquid droplets under an electric field. The driving electrodes laid on glass are scaled at some tens of µm. The achieved demonstrators allow basic manipulation : cutting of a droplet from an inlet reservoir and its transporting over a few electrode network but also joining two droplets. Finally the concept of dielectrophoretic transport is examined in view to handle conducting biological liquids which can recover a dielectric behaviour under a high frequency electric field.

Analytical model of a dual frequency capacitive sheath

In recent years, there has been an increased interest in capacitively coupled plasma discharges which are operated with two frequencies. An analytical sheath model for a capacitively coupled radio-frequency plasma discharge operated with two frequencies is proposed and studied under the assumptions of a time-independent, collisionless ion motion. Expressions are obtained for the time-average electric potential within the sheath, nonlinear motion of the electron sheath boundary and nonlinear instantaneous sheath voltage. The derived model is valid under the condition that the low frequency (lf) electric field Elf in the sheath is much higher than the high frequency (hf) electric field Ehf. This condition is fulfilled within typical dual frequency conditions. It is shown, however, that the hf electric field modifies the sheath structure significantly because of the electron response to Ehf. This model has been compared to particle-in-cell plasma simulations, finding good quantitative agreement. We present the dependence of the maximum sheath width and the dc sheath voltage drop on the hf/lf current ratio and on the hf/lf frequency ratio.

An Experimental Investigation on Frost Control Using DC and AC Electric Fields on a Horizontal, Downward-Facing Plate

The effects of DC and AC electric fields on frost formation on a horizontal downward-facing flat plate was investigated in the present experimental study. Frost growth was influenced and controlled by electric fields generated by an insulated wire electrode. In order to quantify the effects of DC and AC electric fields on frost growth, both mass transfer and frost height were measured. Experiments were carried out in a test section where environmental conditions including air temperature, humidity, and flow rate were controlled. When an AC electric field (with frequency ranging from 135 to 1000 Hz) was applied at predefined time intervals, the frost mass reduction ranged from 12% to 36%, while the frost height reduction was between 22% and 33%. On the other hand, continuous application of high voltage and high frequency (above 100 Hz) electric fields was found to increase the mass of frost by as much as 44% while strongly reducing the frost height (up to 65%). An intermittent DC electric field showed interesting effects on frost formation, with a mass frost reduction of up to 10%.