Radio Frequency Voltage Research Articles

Resonance of magnetization excited by voltage in magnetoelectric heterostructures

Manipulation of magnetization dynamics is critical for spin-based devices. Voltage driven magnetization resonance is promising for realizing low-power information processing systems. Here, we show through Finite Element Method (FEM) simulations that magnetization resonance in nanoscale magnetic elements can be generated by a radio frequency (rf) voltage via the converse magnetoelectric (ME) effect. The magnetization dynamics induced by voltage in a ME heterostructures is simulated by taking into account the magnetoelastic and piezoelectric coupling mechanisms among magnetization, strain and voltage. The frequency of the excited magnetization resonance is equal to the driving rf voltage frequency. The proposed voltage driven magnetization resonance excitation mechanism opens a way toward energy-efficient spin based device applications.

Effect of Parallel-Plate Geometry on Mode Transition Behavior in Argon Microplasmas: Two-Dimensional Simulation**Supported by the Fundamental Research Funds in Heilongjiang Provincial Universities of China under Grant No 135209312.

A two-dimensional self-consistent fluid model is employed to investigate radio-frequency process parameters on the plasma properties in Ar microdischarges. The neutral gas density and temperature balance equations are taken into account. We mainly investigate the effect of the electrode gap on the spatial distribution of the electron density and electron temperature profiles, due to a mode transition from the γ regime (secondary electrons emission is responsible for the significant ionization) to the α regime (sheath oscillations and bulk electrons are responsible for sustaining discharge) induced by a sudden decrease of electron density and electron temperature. The pressure, radio-frequency sources frequency and voltage effects on the electron density are also elaborately investigated.

Randomizing phase to remove acousto-optic device wiggle errors for high-resolution optical tweezers

Acousto-optic (AO) devices have been used extensively in optical tweezers because of their flexibility and speed; however, these devices have trap positioning inaccuracies that limit their usefulness, especially for high-resolution applications. We show that these inaccuracies are due to interference patterns within the AO device sound fields. We have devised a method that removes these inaccuracies by reducing the coherence of the sound fields by directly controlling and randomizing the phase of the radio frequency voltage input signal. We demonstrate that the trapping inaccuracies are eliminated, for both constant trap position and force-ramp measurements, and that no additional noise is added. We show that this random phase method is applicable to both acousto-optic modulator and deflector type devices and can be easily integrated via software upgrade into existing instruments.

Rotation relaxation splitting for optimizing parallel RF excitation pulses with [formula omitted]- and [formula omitted]-relaxations in MRI

Exact solutions of the Bloch equations with T1- and T2-relaxation terms for piecewise constant magnetic fields are numerically challenging. We therefore investigate an approximation for the achieved magnetization in which rotations and relaxations are split into separate operations. We develop an estimate for its accuracy and explicit first and second order derivatives with respect to the complex excitation radio frequency voltages. In practice, the deviation between an exact solution of the Bloch equations and this rotation relaxation splitting approximation seems negligible. Its computation times are similar to exact solutions without relaxation terms. We apply the developed theory to numerically optimize radio frequency excitation waveforms with T1- and T2-relaxations in several examples.

Radio-Frequency Ion Thrusters—Power Measurement and Power Distribution Modeling

We present a methodology to measure the power delivered to sustain an inductive plasma discharge inside radio-frequency ion thrusters. This measurement is performed in real time near the coil within the resonant circuit using a patented low-noise radio-frequency voltage and current sensor system. With knowledge of the actual forwarded power, the efficiency of the generator under consideration, including the power feed cable, is assessed in real time. The variation of the power-to-thrust ratio can thus be understood more clearly since its value is given by physical changes of the plasma properties as well as the quality of the impedance bridge between the generator and plasma load. The latter can directly be determined by the proposed methodology, while the influence of the plasma parameters on the power-to-thrust ratio is obtained by means of a numerical model that is used in postprocessing to assess the power distribution within the thruster.

Low-vacuum cylindrical ion trap mass spectrometry

ABSTRACTLow-vacuum mass spectrometry is desirable because it reduces the size, weight, cost, and power of the instrument by reducing the workload of the pumping system. To investigate low-vacuum mass spectrometry methods, a cylindrical ion trap (CIT) instrument was built. The platform used an electron impact source as the ionization source, a custom CIT as the mass analyzer, and an electron multiplier as the ion detector. The dimensions of the CIT were r0 = 10 mm and z0 = 8.98 mm. Aiming at low-vacuum conditions, its working parameters were optimized. By increasing the frequency of the radio frequency (RF) voltage, optimizing the electron impact source, using a higher voltage on the electron multiplier, and improving the current preamplifier, the mass spectrometry of methyl salicylate was successively performed at helium buffer gas pressures up to 2 Pa, which was dozens of times higher than the upper pressure limit of ion trap mass spectrometers. More importantly, this pressure can be obtained using a single pump, avoiding the use of a bulky turbo pump. In addition, we measured and analyzed the mass deviation of methyl salicylate with the changes in the background gas pressure and RF voltage frequency. The results experimentally verified the theory that the stability regions expand with increasing pressure for the first time. The methods we explored could be used to develop next generation hand-portable instruments and bring new applications to mass spectrometry.

Transient MHD Couette Flow in a Rotating Environment Permeated by an Inclined Magnetic Field by Means of a Traveling Magnetic Field Subject to a Forced Oscillation

The present investigation reveals to a magnetohydrodynamic (MHD) start up flow of a rotating environment permeated by a traveling magnetic field with reference to a periodic driving force to explore the behaviour of a magnetic field at the resonant level. In a time varying electromagnetic field of sinusoidal in nature subject to ∇⋅≠0, an oscillating current flow emerges the backbone of a radio emission in which the emission of hot electron gyrates in a magnetic field in the presence of a radiofrequency accelerator. The expedition of a radiofrequency field determines X-emission to expedite radiofrequency voltage under the influence of A.C circuit subject to ∇⋅≠0. An oscillating current flow deals with an excitation frequency in such a way that phase angle rotates with angular frequency, the magnetic field grows towards the resonant level when the phase angle ωτ=π/2 is compatible with ω>0. In turn, plasma induced laser radiation is influenced by an oscillator with a decisive importance to an excitation frequency in the presence of a magnetic mirror so that maximum reflection occurs as the magnetic field increase in strength abruptly to exhibit resonance fluorescence. A synchronized laser photon light in transmitted from the Sun subject to ωτ=π/2.

Precise positioning of an ion in an integrated Paul trap-cavity system using radiofrequency signals

We report a novel miniature Paul ion trap design with an integrated optical fibre cavity which can serve as a building block for a fibre-linked quantum network. In such cavity quantum electrodynamic set-ups, the optimal coupling of the ions to the cavity mode is of vital importance and this is achieved by moving the ion relative to the cavity mode. The trap presented herein features an endcap-style design complemented with extra electrodes on which additional radiofrequency voltages are applied to fully control the pseudopotential minimum in three dimensions. This method lifts the need to use three-dimensional translation stages for moving the fibre cavity with respect to the ion and achieves high integrability, mechanical rigidity and scalability. Not based on modifying the capacitive load of the trap, this method leads to precise control of the pseudopotential minimum allowing the ion to be moved with precisions limited only by the ion’s position spread. We demonstrate this by coupling the ion to the fibre cavity and probing the cavity mode profile.

Scaling laws for AC gas breakdown and implications for universality

The reduced dependence on secondary electron emission and electrode surface properties makes radiofrequency (RF) and microwave (MW) plasmas advantageous over direct current (DC) plasmas for various applications, such as microthrusters. Theoretical models relating molecular constants to alternating current (AC) breakdown often fail due to incomplete understanding of both the constants and the mechanisms involved. This work derives simple analytic expressions for RF and MW breakdown, demonstrating the transition between these regimes at their high and low frequency limits, respectively. We further show that the limiting expressions for DC, RF, and MW breakdown voltage all have the same universal scaling dependence on pressure and gap distance at high pressure, agreeing with experiment.

Performance enhancement of high-field asymmetric waveform ion mobility spectrometry by applying differential-RF-driven operation mode.

The traditional operation mode of high-field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) uses a one-way radio frequency (RF) voltage input as the dispersion voltage. This requires a high voltage input and limits power consumption reduction and miniaturization of instruments. With higher dispersion voltages or larger compensation voltages, there also exist problems such as low signal intensity or the fact that the dispersion voltage is no longer much larger than the compensation voltage. In this paper, a differential-RF-driven operation mode of FAIMS is proposed. The two-way RF is used to generate the dispersion field, and a phase difference is added between the two RFs to generate a single step waveform field. Theoretical analysis, and experimental results from an ethanol sample, showed that the peak positions of the ion spectra changed linearly (R2 = 0.9992) with the phase difference of the two RFs in the differential-RF-driven mode and that the peak intensity of the ion spectrum could be enhanced by more than eight times for ethanol ions. In this way, it is possible to convert the ion spectrum peaks outside the separation or compensation voltage range into a detectable range, by changing the phase difference. To produce the same separation electric field, the high-voltage direct current input voltage can be maximally reduced to half of that in the traditional operation mode. Without changing the drift region size or drift condition, the differential-RF-driven operation mode can reduce power consumption, increase signal-to-noise ratio, extend the application range of the dispersion voltage and compensation voltage, and improve FAIMS detection performance.

A finite element procedure for radio-frequency sheath–plasma interactions based on a sheath impedance model

A finite element code that solves self-consistent radio-frequency (RF) sheath–plasma interaction problems is improved by incorporating a generalized sheath boundary condition in the macroscopic solution scheme. This sheath boundary condition makes use of a complex sheath impedance including both the sheath capacitance and resistance, which enables evaluation of not only the RF voltage across the sheath but also the power dissipation in the sheath. The newly developed finite element procedure is applied to cases where the background magnetic field is perpendicular to the sheath surface in one- and two-dimensional domains filled by uniform low- and high-density plasmas. The numerical results are compared with those obtained by employing the previous capacitive sheath model at a typical frequency for ion cyclotron heating used in fusion experiments. It is shown that for sheaths on the order of 100 V in a high-density plasma, localized RF power deposition can reach a level which causes material damage. It is also shown that the sheath–plasma wave resonances predicted by the capacitive sheath model do not occur when parameters are such that the generalized sheath impedance model substantially modifies the capacitive character of the sheath. Possible explanations for the difference in the maximum RF sheath voltage depending on the plasma density are also discussed.

Mechanisms of sustaining a radio-frequency atmospheric pressure planar discharge

The time behavior of an atmospheric pressure planar discharge sustained in He gas was investigated experimentally and through two dimensional (2D) discharge simulation. The 30 mm long uniform α-mode discharge was observed at radio frequency (RF) input power below 35 W. The gas temperature of 375 ± 50 K in the discharge core was estimated by emission spectroscopy of OH(A–X) emission. A sheath region of about 100–150 μm width near both electrodes was observed during the whole RF cycle. However, there were differences in emission dynamics among various species detected in the discharge. OH(A) emission does not follow the RF voltage temporal variation. Strong He emission was always detected near the cathode, which was consistent with the 2D discharge simulation results. He-excited species production was found mainly due to the electron impact process. The simulation showed that both the electron and ion density vary from 1.88 × 1017 m−3 to 1.92 × 1017 m−3, and the electron temperature was about 1.85 eV in the plasma bulk. The ion temperature stayed close to the rotational temperature of OH radicals, and only increased near the sheath region to 0.65 eV. It was found that the mechanism of the sheath formation in atmospheric pressure discharge strongly correlates with the dynamics of the electron density and electron temperature variation in the gap, and the process is similar to low pressure RF capacitively coupled discharges. The high uniformity of the discharge and the upscale possibility to any desirable size are considered beneficial for industrial applications of the source, which is key for processes of thin coating deposition and polymer modification.

Miniaturized magnet-less RF electron trap. II. Experimental verification

Atomic microsystems have the potential of providing extremely accurate measurements of timing and acceleration. However, atomic microsystems require active maintenance of ultrahigh vacuum in order to have reasonable operating lifetimes and are particularly sensitive to magnetic fields that are used to trap electrons in traditional sputter ion pumps. This paper presents an approach to trapping electrons without the use of magnetic fields, using radio frequency (RF) fields established between two perforated electrodes. The challenges associated with this magnet-less approach, as well as the miniaturization of the structure, are addressed. These include, for example, the transfer of large voltage (100–200 V) RF power to capacitive loads presented by the structure. The electron trapping module (ETM) described here uses eight electrode elements to confine and measure electrons injected by an electron beam, within an active trap volume of 0.7 cm3. The operating RF frequency is 143.6 MHz, which is the measured series resonant frequency between the two RF electrodes. It was found experimentally that the steady state electrode potentials on electrodes near the trap became more negative after applying a range of RF power levels (up to 0.15 W through the ETM), indicating electron densities of ≈3 × 105 cm−3 near the walls of the trap. The observed results align well with predicted electron densities from analytical and numerical models. The peak electron density within the trap is estimated as ∼1000 times the electron density in the electron beam as it exits the electron gun. This successful demonstration of the RF electron trapping concept addresses critical challenges in the development of miniaturized magnet-less ion pumps.

Characterization of narcotics using differential mobility spectrometry

The topic of this work is the use of differential mobility spectrometry for the characterization of narcotics. Studies were performed for amphetamine, methamphetamine, ketamine, heroin, and cocaine dissolved in methanol. Each target molecule appears at a specific compensation voltage under a fixed value of radiofrequency (RF) voltage. Values of compensation voltage of product ion peak at RF = 1480 V for cocaine, heroin, ketamine, methamphetamine, and amphetamine at 110 °C appears at 3.33, 2.43, 2.12, −0.56, and −4.9 V, respectively. Nonlinear function curves were used for graphical differentiation of measured narcotics. This study also deals with the effects of temperature on peak position in differential mobility spectra. This rapidly developed method allows characterization of five illicit drugs in 100 s.

Emission characteristics of 6.78-MHz radio-frequency glow discharge plasma in a pulsed mode

This paper investigated Boltzmann plots for both atomic and ionic emission lines of iron in an argon glow discharge plasma driven by 6.78-MHz radio-frequency (RF) voltage in a pulsed operation, in order to discuss how the excitation/ionization process was affected by the pulsation. For this purpose, a pulse frequency as well as a duty ratio of the pulsed RF voltage was selected as the experimenter parameters. A Grimm-style radiation source was employed at a forward RF power of 70W and at an argon pressures of 670Pa. The Boltzmann plot for low-lying excited levels of iron atom was on a linear relationship, which was probably attributed to thermal collisions with ultimate electrons in the negative glow region; in this case, the excitation temperature was obtained in a narrow range of 3300–3400K, which was hardly affected by the duty ratio as well as the pulse frequency of the pulsed RF glow discharge plasma. This observation suggested that the RF plasma could be supported by a self-stabilized negative glow region, where the kinetic energy distribution of the electrons would be changed to a lesser extent. Additional non-thermal excitation processes, such as a Penning-type collision and a charge-transfer collision, led to deviations (overpopulation) of particular energy levels of iron atom or iron ion from the normal Boltzmann distribution. However, their contributions to the overall excitation/ionization were not altered so greatly, when the pulse frequency or the duty ratio was varied in the pulsed RF glow discharge plasma.

An All-Passive Negative Feedback Network for Broadband and Wide Field-of-View Self-Steering Beam-Forming With Zero DC Power Consumption

This paper presents an all-passive negative feedback network that performs autonomous radio-frequency (RF) front-end beam-forming and dynamic beam-tracking toward the direction of the incident RF signal. The proposed feedback network consists of a passive RF signal processing network, voltage rectifiers, and voltage-controlled delay-line phased shifters, all of which are passive-only circuits. The negative feedback loop is realized by passive phase detection, phase-to-voltage conversion, and voltage-controlled phase shifting, achieving a large loop-gain and autonomous operation with zero DC power consumption. The nonlinear behavior of the loop is exploited to substantially expand the array field of view (FoV). A proof-of-concept broadband four-element all-passive self-steering beam-former at 5 GHz with a wide FoV is implemented in a standard 130 nm CMOS process. A high-quality four-element synthesized array factor is measured for the input progressive phase shift $\phi _{\mathrm {in}}$ from −180° to 180°. When the proposed negative feedback loop is enabled, the normalized array factor is −2.87/−2.8 dB at $\phi _{\mathrm {in}}= + 90^{\circ }$ /−90° with an input RF power $\text{P}_{\mathrm {in}}$ of −17 dBm/element at 5 GHz, achieving >25 dB array factor improvement over the open-loop operation. Moreover, the nonlinear feedback loop allows for significant array factor improvement even at $\phi _{\mathrm {in}} = +180^{\circ }$ /−180°. The proposed beam-former also achieves high-quality self-steering beam-forming from 4 to 5.68 GHz with 34.7% fractional bandwidth. Therefore, the proof-of-concept all-passive self-steering beam-former outperforms the state-of-the-art active designs in terms of beam-forming quality, FoV, and fractional bandwidth. To the best of the authors’ knowledge, this is the first demonstration of an all-passive negative feedback network for a broadband and wide FoV self-steering beam-forming with zero DC power consumption.

Investigation of NO removal using a pulse-assisted RF discharge

In this paper, removal of nitrogen oxide (NO) is investigated in capacitive atmospheric pressure discharges driven by both radio-frequency (RF) and trapezoidal pulsed power with a one-dimensional self-consistent fluid model. The results show that the number density of NO could be reduced significantly once a short pulse of low duty ratio is additionally applied to the RF power. It is found that the process of NO removal by the pulse-modulated RF discharge could be divided into three stages: the quick reaction stage, the NO removal stage, and the sustaining stage. Furthermore, the temporal evolution of particle densities is analyzed, and the key reactions in each stage are discovered. Finally, the influence on the removal efficiency of the voltage amplitude of the pulse and the RF voltage amplitude is investigated.

Design and Construction of a Helical Resonator for Delivering Radio Frequency to an Ion Trap

Supplying high voltage radio frequency (RF) is a critical part of ion trapping system due to impedance mismatching between RF source and the ion trap. A helical resonator has been constructed in order to deliver narrow bandwidth and high voltage RF to the ion trap for stable confinement of ions. The performances of the helical resonator have been studied for different capacitive load of the ion trap. Both the resonant frequency and quality factor of the resonator show strong dependence on external capacitive loads.

Laser ablation production of Ba, Ca, Dy, Er, La, Lu, and Yb ions

We use a pulsed nitrogen laser to produce atomic ions by laser ablation, measuring the relative ion yield for several elements, including some that have only recently been proposed for use in cold trapped ion experiments. For barium, we monitor the ion yield as a function of the number of applied ablation pulses for different substrates. We also investigate the ion production as a function of the pulse energy, and the efficiency of loading an ion trap as a function of radiofrequency voltage.

Theoretical and experimental analysis of amplitude control ablation and bipolar ablation in creating linear lesion and discrete lesions for treating atrial fibrillation

Purpose: Radiofrequency (RF) energy is often used to create a linear lesion or discrete lesions for blocking the accessory conduction pathways for treating atrial fibrillation. By using finite element analysis, we study the ablation effect of amplitude control ablation mode (AcM) and bipolar ablation mode (BiM) in creating a linear lesion and discrete lesions in a 5-mm-thick atrial wall; particularly, the characteristic of lesion shape has been investigated in amplitude control ablation.Materials and methods: Computer models of multipolar catheter were developed to study the lesion dimensions in atrial walls created through AcM, BiM and special electrodes activated ablation methods in AcM and BiM. To validate the theoretical results in this study, an in vitro experiment with porcine cardiac tissue was performed.Results: At 40 V/20 V root mean squared (RMS) of the RF voltage for AcM, the continuous and transmural lesion was created by AcM-15s, AcM-5s and AcM-ad-20V ablation in 5-mm-thick atrial wall. At 20 V RMS for BiM, the continuous but not transmural lesion was created. AcM ablation yielded asymmetrical and discrete lesions shape, whereas the lesion shape turned to more symmetrical and continuous as the electrodes alternative activated period decreased from 15 s to 5 s. Two discrete lesions were created when using AcM, AcM-ad-40V, BiM-ad-20V and BiM-ad-40V. The experimental and computational thermal lesion shapes created in cardiac tissue were in agreement.Conclusions: Amplitude control ablation technology and bipolar ablation technology are feasible methods to create continuous lesion or discrete for pulmonary veins isolation.