Radio Frequency Voltage Research Articles

A 2.4 GHz receiver with a current-reused inductor-less noise-canceling balun LNA in 40 nm CMOS

A low power receiver is designed and implemented for 2.4 GHz Industrial-Scientific-Medical (ISM) band in a 40 nm CMOS process. To obtain good noise and linearity performance at low cost, a current-reused low power inductor-less balun low noise amplifier (LNA) structure is proposed without use of monolithic spiral inductors or transformers. The receiver adopts a zero-IF architecture and current mode mixing operation which avoid need of large voltage headroom for the radio frequency (RF) voltage swing under strong interferers. A third order active-RC low pass filter (LPF) with RC calibration and DC offset cancelation (DCOC) blocks are carefully designed. Current reusing technique and timing optimized asynchronous SAR logic are adopted in LNA and ADC design respectively, featuring high-power efficiency. The total receiver chain achieves maximum conversion gain of 80.32 dB, noise figure (NF) of 6.27 dB and input referred third-order intercept point (IIP3) of −0.6 dBm with 32.8 mW power consumption.

An analytical approach to symmetry breaking in multipole RF-traps

Radio-frequency (RF) linear multipole traps have been shown to be very sensitive to mis-positioning of their electrodes, which results in a symmetry breaking and leads to extra local minima in the trapping potential as shown in Pedregosa-Gutierrez et al (2018 J. Mod. Opt. 65 529) disturbing the operation of the trap. In this work, we analytically describe the RF-potential of a realistic octupole trap by including lower order terms to the well-established equation for a perfectly symmetric octupole trap. We describe the geometry by a combination of identified defects, characterized by simple analytical expressions. A complete equation is proposed for a trap with any electrode deviation relying on a combination of the simple cases where the defects are taken individually. Our approach is validated by comparison between analytical and numerical results for defect sizes up to 4% of the trap radius. As described in Pedregosa-Gutierrez et al (2018 Rev. Sci. Instrum. 89 123101), an independent fine-tuning of the amplitude of the RF voltage applied on each electrode can be used to mitigate the geometrical defects of a realistic trap. In a different way than in Pedregosa-Gutierrez et al (2018 Rev. Sci. Instrum. 89 123101), the knowledge of an analytical equation for the potential allows to design the set of RF-voltages required for this compensation, based on the experimental measurement of the ion positions in the trap, without information concerning the exact position of each electrode, and with a small number of iterations. The requirements, performances and limitations of this protocol are discussed via comparison of numerical simulations and analytical results.

Effects of collision-enhanced charging on dust crystal

Numerical simulations of monolayer dust crystals in a radio frequency (RF) complex plasma were performed to examine the crystal structure and quantify the effects of including the collision-enhanced ion current in the charging model. A gaseous electronics conference (GEC) cell similar to a previous experimental work was modeled for a range of RF voltages, using a continuum description for the plasma and a particle description for dust grains. The time history of each dust grain was monitored. The dust charge was computed using both the orbital motion limited and the collision-enhanced charging (CEC) model applicable to the sheath region. The dust model accounted for the electric force, ion drag force, neutral drag force, gravity, and the ion wake. The CEC model produced a lower charge and lower electric force which agreed better with the experimental data. Then dust crystals composed of 40–100 grains were modeled and the levitation height and inter-particle spacing of the resulting crystals was examined. Including the collision-enhanced current reduced the inter-particle spacing but only had a minor effect on the levitation height.

Intrasheath electron dynamics in low pressure capacitively coupled plasmas

We present a detailed analysis of electron trajectories within the sheath regions of capacitively coupled plasmas excited by radio-frequency voltage waveforms at low pressures. Complex features inside the sheaths are identified in several physical quantities, which are sculptured by the trajectories of bouncing energetic electrons (predominantly ion induced secondary electrons) under the influence of the spatio-temporally varying electric field. Based on a systematic parameter variation the generation of the various features as a function of surface processes is explained and the trajectories of electrons of different origin are identified.

Simulations of standing wave effect, stop band effect, and skin effect in large-area very high frequency symmetric capacitive discharges

In this paper, Maxwell equations are coupled with a radially localized global model and an analytical sheath model to investigate the electromagnetic effects under various frequencies and electron powers in large-area very high frequency symmetric capacitive argon discharges. Simulation results indicate that both the vacuum wavelength and the sheath width decrease with frequency, leading to the reduced surface wavelength. As a result, the standing wave effect becomes pronounced, causing the fact that the radial profiles of the electron density, radio frequency voltage, and sheath width shift from uniform over center-high to multiple-node. When the frequency is close to or higher than the series resonance frequency, the surface waves cannot propagate to the radial center because of the significant radial damping. Due to the lack of power deposition near the radial center, the electron density is nearly zero there, i.e. the stop band effect. As power increases, the higher electron density leads to the decrease of the skin depth. Therefore, the importance of the skin effect gradually exceeds that of the standing wave effect, giving rise to the transition from the center-high to edge-high electron density profiles. The method proposed in this work could help to predict the plasma distribution under different discharge conditions in a few minutes, which is of significant importance in optimizing the plasma processing.

Simultaneous optimization of radio frequency and gradient waveforms with exact Hessians and slew rate constraints applied to [formula omitted]-points excitation

We consider an excitation pulse with piecewise constant gradient trajectories and radio frequency (RF) waveforms such that the solution of the Bloch equations without relaxation terms can be represented by rotations. Based on this analytic solution we formulate a non-linear program for finding sub-pulse durations, gradient strengths, and complex RF voltages which minimize the deviation between the achieved and desired magnetization. We develop explicit expressions for the first and second order derivatives of the objective function. We extend the non-linear program to precisely account for gradient slew rate constraints. Using an interior point solver we apply the developed theory to simultaneously optimize the positions of kT-points, their associated RF voltages and durations.

Power Dither Technique for Measuring the RF Half-Wave Voltage of a Silicon Mach–Zehnder Modulator

A novel method to measure the radio frequency(RF) half-wave voltage of the silicon Mach-Zehnder modulator (SMZM) is presented based on a low-frequency power dither signal. In our method, the power dither is applied to the thermo-optic phase shifter built into the SMZM, and an RF modulation signal applied to the SMZM is produced by a pulse-code generator. Then, a low-frequency monitor photodiode is used to detect the output signal of the SMZM, and a pair of orthogonal trigonometric functions with the same frequency as the power dither signal is constructed. This performs the cross-correlation integral operations with the output signal of the SMZM. The aforementioned integral results versus different amplitude RF modulation signals are plotted as two third-order polynomial functions, and the intersection point of the third-order polynomial functions corresponding to the RF voltage is the half-wave modulation voltage. Compared with the conventional methods, this new method not only removes the electrical absorption effect and nonlinear electro-optic effect of the SMZM-induced measurement error but also improves measurement accuracy and reduces measurement complexity.

A New Measurement Method for High Voltages Applied to an Ion Trap Generated by an RF Resonator.

A new method is proposed to measure unknown amplitudes of radio frequency (RF) voltages applied to ion traps, using a pre-calibrated voltage divider with RF shielding. In contrast to previous approaches that estimate the applied voltage by comparing the measured secular frequencies with a numerical simulation, we propose using a pre-calibrated voltage divider to determine the absolute amplitude of large RF voltages amplified by a helical resonator. The proposed method does not require measurement of secular frequencies and completely removes uncertainty caused by limitations of numerical simulations. To experimentally demonstrate our method, we first obtained a functional relation between measured secular frequencies and large amplitudes of RF voltages using the calibrated voltage divider. A comparison of measured relations and simulation results without any fitting parameters confirmed the validity of the proposed method. Our method can be applied to most ion trap experiments. In particular, it will be an essential tool for surface ion traps which are extremely vulnerable to unknown large RF voltages and for improving the accuracy of numerical simulations for ion trap experiments.

Real-time continuous measurement of intraoperative trace exhaled propofol by planar differential mobility spectrometry.

In order to study anesthetic pharmacokinetics and adequately adjust the anaesthesia depth of patients, real-time measurement of the intraoperative exhaled propofol concentration is of significant importance for anaesthetists. Although a series of analytical techniques and methods have been developed for the detection of exhaled propofol, differential mobility spectrometry (DMS) with the advantages of a much smaller instrument, faster response time and cheaper cost shows great potential for the point of care in the operating room. In this paper, a planar DMS was constructed for real-time continuous measurement of trace propofol in exhaled air. The effects of DMS parameters, such as the radio frequency voltage, the drift gas flow rate and the sampling flow rate of exhaled air on the propofol measurement under high humidity conditions were carefully investigated and discussed. Under the optimum experimental conditions, the limit of detection (LOD) for propofol was achieved in ppbv with a linear range of 0.5 to 25 ppbv, both of which meet clinical requirements. Finally, the planar DMS was performed on a patient undergoing thyroidectomy surgery to real-time monitor the intraoperative exhaled propofol, which demonstrated the capability of DMS for sensitive and breath-by-breath continuous measurement of intraoperative trace exhaled propofol.

Retrospective Analysis of Treatment Results by Non-Invasive Radiofrequency (RF) Device with Standard and High Voltage RF Electrical Pulses Coupled with Suction for Fat Reduction and Cellulite Improvement

Introduction: The growing demand for non-surgical, non-invasive procedures for fat and circumference reduction and for cellulite treatments has led to the development of various energy-based technologies. Bi-polar radiofrequency (RF) technology combined with additional technologies, such as vacuum, massage or infrared (IR) light is widely used in various body contouring treatments in the medical aesthetic market. The current study is based on a retrospective efficacy analysis of an RF device, combining two RF modalities, coupled with suction. Methods: Representative treatment outcomes, documented in photographs taken at baseline and post-treatment were gathered from several clinics. Photos of the various treatment areas were evaluated by independent evaluators for cellulite and contour improvement. Results: Before and after photographs were gathered from 31 patients treated in different clinics. Analysis was carried out on different body areas such as thighs, abdomen, back, buttocks and arms and analyzed by two independent evaluators. Scoring was performed according to the Global Aesthetic Improvement Scale (GAIS) scale and indicated an overall improvement in the contour of all treated body areas. In cellulite cases, improved appearance according to the cellulite grading scale was noted. Conclusion: This retrospective analysis supports the device’s efficacy for fat and circumferences reduction and cellulite improvement. The device’s unique specifications contribute to treatment safety and efficacy which is highly tolerable by the patients.

Radio-Frequency Ion Guides with Periodical Electrodes and Pulse Voltages

We consider radio-frequency ion guides formed by electrodes, which are periodic sequences of circular apertures. With the help of pulse voltages arranged as trains of a special type, a relay-switched sequence of axial distributions of the pseudopotential can be organized along the axis of the system in the form of space waves with alternating maxima and minima, which convey charged particles along the conveying channel. The disadvantage of the proposed conveying technology is the obligatory presence of neutral gas in moderate amounts, which dampens the excess kinetic energy acquired by charged particles in the jump-like switching of the radio-frequency electric field. An advantage of the proposed conveying technology is the simplified form of radio-frequency voltages applied to the electrodes of the device and the flexible control of the guiding velocity in Gas Chromatography–Mass Spectrometry interfaces, for example.

Analysis and design of a novel high capacitance ratio and low actuation voltage RF MEMS switch

Analysis and design of a novel high on/off capacitance ratio and low actuation voltage radio frequency microelectro-mechanical systems (RF MEMS) switch. Circuit topology and electrode topology of RF MEMS switches are analyzed. In order to decrease actuation voltage, the switch, using coplanar waveguide transmission line for signal transmission, are designed with special elastic supported structures and actuation electrode are located on both sides of signal line. Metal–insulator–metal (MIM) fixed capacitors are used to change the up/down-state capacitance without adding more loss to the switches. Through the finite element method to determine the spring constant and the necessary applied voltage, the simulation voltage is 4.5 V. The RF performance are obtained by simulating results in the HFSS tool. The switch exhibits the insertion loss of – 0.2 dB, and isolation of – 20 dB within the range of 10–30 GHz, and the isolation extreme value reaches − 41 dB at resonant frequency, the return loss is less than − 12 dB at the resonant frequency. From the fitted results, the on/off capacitance ratio is 162 for the MEMS switch. Compared with traditional MEMS capacitive switches, the proposed MEMS switch exhibit high on/off capacitance ratios and low actuation voltage.

Considerations for Harmonics Distribution in Aperture-Tuned Inverted-F Antenna for Cellular Handheld Devices

An analysis of the harmonics distribution in the aperture-tuned inverted-F antenna (IFA) using the first-order transmission line model is presented. The analysis allows identifying local minimums for the second and third harmonics for a given use case, providing the mechanism for optimization of the nonlinear performance of an antenna system. The theoretical findings are verified on a hardware demonstrator, comprising a mechanically reconfigurable IFA and a single-pole single-throw (SPST)-based aperture tuning network. The aperture tuning network comprises a radio frequency (RF) high-voltage switch, including a voltage detector with low-harmonic feedback and a parallel inductor. The integrated circuit (IC) was fabricated in Infineon 130-nm dedicated RF switch technology. The hardware demonstrator enables the measurements of the impedance at the feed, harmonics, RF voltage along the radiating element, and impedance at aperture tuning port. The latter provides a mechanism for optimization of load impedance at integer multiplies of transmitted frequencies, which allows minimization of harmonic content generated by the tuning IC.

Low level Radio Frequency studies for the Compact Linear Collider Damping Rings

The Compact Linear Collider (CLIC) Damping Rings (DRs) need to generate ultra-low emittance bunches to achieve high luminosity in CLIC. Strong wiggler magnets are required to significantly increase the energy loss per turn. A high total voltage Radio Frequency (RF) system is needed to compensate these losses. The resulting strong beam loading transients affect the bunch position and length. On the other hand, in order to maintain the luminosity loss below 1%, the bunch position has to be regulated within ±1∘ at 2 GHz (±400μm) at the DR extraction. These conflicting specifications lead to a challenging design for the Low-Level RF (LLRF) system. In this work, simulations of the LLRF system are presented and validated using theoretical expressions. They are then used to evaluate various potential LLRF architectures, and to estimate and compare their performance to the demanding specifications on bunch longitudinal position in the CLIC DRs.

Mass filter with phase modulation of radio frequency voltage.

In this work, the parametric quadrupole resonance caused by the phase modulation of waveform potential is studied. Based on analytical and numerical description of the ion motion in the quadrupole mass filter with the phase modulation, a stability island is found with good ion optical properties such as high ion transmission efficiency (16%), high mass resolution (peak width measured at 10% of peak height, R0.1 = 6000), the required separation time (100-150 radio frequency [RF] cycles), and good peak shape of trapezoid form. Furthermore, the analysis of the frequency spectrum of the applied potential and the quadrupole mass filter (QMF) acceptance are also presented; a resonance frequency is found from this spectrum. Finally, a suitable stability X-islands with relative modulation frequency, , is established and studied in detail. Here, β is the imaginary part of the characteristic exponent of stable solutions to the Mathieu equation.

On uniformity and non-local transport in low pressure capacitively coupled plasmas

Low pressure (<30 mTorr) capacitively coupled plasmas (CCP) are important for many plasma processing applications. Due to high energy of electrons in these plasmas and long electron mean free path, kinetic phenomena dominate the electron behavior. A multi-dimensional particle-in-cell (PIC) model is utilized to study the physics of sub-100 mTorr Ar CCPs in this article. A one-dimensional model for helium plasma in the 30–300 mTorr pressure range is first used to benchmark the PIC code against published results by Turner et al [2013 Phys. Plasmas 013507]. The article then focuses on two-dimensional modeling of the gaseous electronics conference (GEC) reference cell in cylindrical geometry. Computed ion density and DC bias voltage at 100 mTorr are compared to available experimental data for a range of radio frequency voltages, demonstrating good agreement. The validated model is used to examine Ar plasmas in the GEC reference cell in the 12.5–100 mTorr pressure range. It is found that the peak in ion and electron densities is near the electrode edge at 100 mTorr due to strong electric field there. As the gas pressure decreases, the peak in plasma density moves to the chamber center. This change in plasma spatial profile is linked to kinetic behavior of electrons, both regarding plasma production and transport in the plasma. Time-dependent results are used to illustrate that electron current at 25 mTorr is mainly kinetic and carried by beam electrons generated by expanding sheaths.

Effects of modular ion-funnel technology onto analysis of breath VOCs by means of real-time mass spectrometry

Proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) is a powerful tool for real-time monitoring of trace concentrations of volatile organic compounds (VOCs). The sensitivity of PTR-ToF-MS also depends on the ability to effectively focus and transmit ions from the relatively high-pressure drift tube (DT) to the low-pressure mass analyzer. In the present study, a modular ion-funnel (IF) is placed adjacent to the DT of a PTR-ToF-MS instrument to improve the ion-focusing. IF consists of a series of electrodes with gradually decreasing orifice diameters. Radio frequency (RF) voltage and direct current (DC) electric field are then applied to the electrodes to get the ions focused. We investigated the effect of the RF voltage and DC field on the sensitivity of a pattern of VOCs including hydrocarbons, alcohols, aldehydes, ketones, and aromatic compounds. In a proof-of-concept study, the instrument operating both as normal DT (DC-mode) and at optimal IF conditions (RF-mode) was applied for the breath analysis of 21 healthy human subjects. For the range of investigated VOCs, an improvement of one order of magnitude in sensitivity was observed in RF-mode compared with DC-mode. Limits of detection could be improved by a factor of 2–4 in RF-mode compared with DC-mode. Operating the instrument in RF-mode allowed the detection of more compounds in the exhaled air compared with DC-mode. Incorporation of the IF considerably improved the performance of PTR-ToF-MS allowing the real-time monitoring of a larger number of potential breath biomarkers.Graphical abstract

Thermal impact of replacing constant voltage by low-frequency sine wave voltage in RF ablation computer modeling

Background and objectivesA constant voltage (DC voltage) is usually used in radiofrequency ablation (RFA) computer models to mimic the radiofrequency voltage. However, in some cases a low frequency sine wave voltage (AC voltage) may be used instead. Our objective was to assess the thermal impact of replacing DC voltage by low-frequency AC voltage in RFA computer modeling. MethodsA 2D model was used consisting of an ablation electrode placed perpendicular to the tissue fragment. The Finite Element method was used to solve a coupled electric-thermal problem. Quasi-static electrical approximation was implemented in two ways (both with equivalent electrical power): (1) by a constant voltage of 25 V in the ablation electrode (DC voltage), and (2) applying a sine waveform with peak amplitude of 25√2 V (AC voltage). The frequency of the sine signal (fAC) varied from 0.5 Hz to 50 Hz. ResultsSine wave thermal oscillations (at twice the fAC frequency) were observed in the case of AC voltage, in addition to the temperature obtained by DC voltage. The amplitude of the oscillations: (1) increased with temperature, remaining more or less constant after 30 s; (2) was of up to ±3 °C for very low fAC values (0.5 Hz); and (3) was reduced at higher fAC values and with distance from the electrode (almost negligible for distances > 5 mm). The evolution of maximum lesion depth and width were almost identical with both DC and AC. ConclusionsAlthough reducing fAC reduces the computation time, thermal oscillations appear at points near the electrode, which suggests that a minimum value of fAC should be used. Replacing DC voltage by low-frequency AC voltage does not appear to have an impact on the lesion depth.

Segmentation of dust particles and spatial distribution of ion density in dusty plasmas

In dusty plasmas, dust particles are levitated in balance of electrostatic, ion drag and gravitational forces. These forces depend on the size of the dust particles and discharge conditions. The dust particles can be segmented on the basis of their sizes, i.e., the dust particles are levitated at different positions depending on their sizes. In this work, the dust particles with two different sizes were observed in a plasma and they were divided into segments by changing radio frequency voltage put into the plasma. Meanwhile a numerical model analyzed the forces acting on the dust particles based on ion densities measured in the plasma. The dust particles were horizontally segmented in the plasma depending on their sizes. The lager ones were distributed outside of the smaller ones. This behaviors was explained by balance of the forces on the dust particles derived in the numerical model with the ambipolar diffusion taken into account.

RETRACTED ARTICLE: Direct quantification of iodine in nuclear wastes using DRC-ICP-MS

A method was developed for the direct quantification of iodine in Hanford tank waste using inductively coupled plasma mass spectrometry coupled with a dynamic reaction cell. The following parameters were optimized to lower the 129 m/z background signal and minimize iodine carryover effects: diluent, oxygen gas flow rate, radiofrequency voltage applied to the dynamic reaction cell, and rinse times. The concentration of 129I was 23 ± 1 µg/mL (n = 4, ± 1σ) in the Hanford waste tank 241-AP-107; to our knowledge this work constitutes the first report of iodine concentration in the tank waste.