Voltage Pulse Frequency Research Articles

Micro-Droplets Parameters Monitoring in a Microfluidic Chip via Liquid-Solid Triboelectric Nanogenerator.

The monitoring of micro-droplets parameters is significant to the development of droplet microfluidics. However, existing monitoring methods have drawbacks such as high cost, interference with droplet movement, and even the potential for cross-contamination. Herein, a micro-droplets monitoring method (MDMM) based on liquid-solid triboelectric nanogenerator (LS-TENG) is proposed, which can realize non-invasive and self-powered monitoring of micro-droplets in a microfluidic chip. The droplet frequency is monitored by voltage pulse frequency and a mathematical model is established to monitor the droplet length and velocity. Furthermore, this work constructs micro-droplets sensor (MDS) based on the MDMM to carry out the experiment. The coefficients of determination (R2 ) of the fitting curves of the micro-droplets frequency, length, and velocity monitoring are 0.998, 0.997, and 0.995, respectively. To prove the universal applicability of the MDMM, the micro-droplets generated by different liquid media and channel structures are monitored. Eventually, a micro-droplet monitoring system is built, which can realize the counting of micro-droplets and the monitoring of droplet frequency and length. This work provides a novel approach for monitoring micro-droplets parameters, which holds the potential to advance developments in the field of microfluidics.

Frequency-dependent stimulated and post-stimulated voltage control of magnetism in transition metal nitrides: towards brain-inspired magneto-ionics.

Magneto-ionics, which deals with the change of magnetic properties through voltage-driven ion migration, is expected to be one of the emerging technologies to develop energy-efficient spintronics. While a precise modulation of magnetism is achieved when voltage is applied, much more uncontrolled is the spontaneous evolution of magneto-ionic systems upon removing the electric stimuli (i.e., post-stimulated behavior). Here, we demonstrate a voltage-controllable N ion accumulation effect at the outer surface of CoN films adjacent to a liquid electrolyte, which allows for the control of magneto-ionic properties both during and after voltage pulse actuation (i.e., stimulated and post-stimulated behavior, respectively). This effect, which takes place when the CoN film thickness is below 50 nm and the voltage pulse frequency is at least 100 Hz, is based on the trade-off between generation (voltage ON) and partial depletion (voltage OFF) of ferromagnetism in CoN by magneto-ionics. This novel effect may open opportunities for new neuromorphic computing functions, such as post-stimulated neural learning under deep sleep.

A highly energy-efficient milling of Inconel 718 via modulated short electric arc machining

An excellent and advanced manufacturing method named modulated short electric arc machining (M-SEAM) was proposed in this study to solve the problems of low machining efficiency and high specific energy consumption (SEC) for difficult-to-machine materials in the traditional electric discharge machining (EDM) and electric arc machining (EAM) process.The discharge channel is established by the collision between the electrode and the workpiece. The arc spreads and moves as the electrode rotates. Moreover, the energy balance equation of the modulated arc was established, which revealed that the volt-ampere characteristic is resistive when the frequency of pulse voltage tends to infinity in the steady state, the arc had a large relative thermal inertia, and two stable operating points were analyzed. M-SEAM processing was performed using graphite and Inconel 718 as electrode and workpiece materials, respectively. The results showed a maximum MRR of 49,020 mm3/min, and the relative electrode wear rate (REWR) and SEC were limited to 0.92% and 50.21 kJ/cm3, respectively. The peak current was 1940 A, and the maximum discharge time for a single arc was 328.56 ms.

Адаптивный регулятор мощности индукционной тигельной печи с проводящим ферромагнитным тиглем

A structural model of a high-frequency induction crucible furnace with a conducting ferromagnetic crucible is developed in the Simulink/Matlab environment based on investigations carried out by the authors. The inductor current was calculated using the inductor's resistance and inductance dependences on temperature, frequency, and current. An induction crucible furnace power control system structural model is designed based on the developed model. The output voltage pulse-frequency modulation is used as a furnace power control method. An adaptive power controller for the induction crucible furnace with a conducting ferromagnetic crucible is developed, which includes two channels for control of the power supply source frequency and voltage. It has been determined that the melting with the lowest energy expenditures is obtained in the case of using a power controller with two different adaptive control structures. The controller operates based on the frequency control principle and uses structures depending on the current temperature value. The use of the adaptive power controller with two control channels can significantly reduce the specific electric energy consumption in comparison with automatic frequency adjustment, in particular, by a factor of 1.45 for the IGT-1.6M industrial furnace.

Investigations into machining accuracy and quality in wire electrochemical micromachining under sinusoidal and triangular voltage pulse condition

• Application and optimization of novel pulsed voltage waveforms for improving the process accuracy in Wire-ECMM. • A mathematical analysis of the evolution of machining gap with time under the application of different voltage waveforms. • Finite element modelling for the visualization of current density distribution in the machining zone. • Evaluation of machining quality using three dimensional optical profilometer and SEM images of machined features. • Optimization of triangular pulsed voltage waveform by varying its rise and fall time for improving the process accuracy. Since the past two decades, improving machining accuracy, precision, and quality of machining in Wire-ECMM has been a prime focus of researchers across the globe. Application of high frequency pulse voltage for machining has served the purpose to a large extent. However, with high frequency pulse voltage, machining rate is compromised. Often, the use of very high frequency also necessitates the application of high voltage amplitude which consequently, leads to increased power consumption. To solve this problem, this research proposes the use of sinusoidal voltage waveform (SVW) and triangular voltage waveform (TVW) instead of a conventionally used rectangular voltage waveform (RVW) for machining. A mathematical analysis of the machining gap in the process using a mechanistic approach suggests that accuracy in terms of kerf width improves significantly when SVW and TVW are used for machining. Experiments are conducted to investigate the impact of pulse voltage waveform on different characteristic features of a kerf profile which are kerf width, edge fillet radius, corner radius, and taper angle. These waveforms are generated using a function generator with the help of a rectification cum amplification electronic circuit. Roughness of the surface machined using these three waveforms are also measured using optical profilometer. Experimental results suggest that the percent reduction in the kerf width for the three waveforms considered by changing the frequency of voltage pulse from 100 kHz to 200 kHz is significantly lower than that obtained by switching from RVW to TVW and keeping other pulse parameters such as frequency, amplitude, and duty ratio same. Using a wire (tool) made of tungsten and a diameter of 30 μm, minimum kerf width of 60 ± 2 μm, edge fillet radius of 11 ± 1 μm, and a negligible corner radius is obtained when TVW is used for machining. For the above stated parameters, profile roughness (R a ) & area surface roughness (S a ) of machined kerf are 1.43 μm and 1.55 μm respectively for RVW, which are reduced to 0.44 μm and 0.57 μm respectively, for TVW. To understand the reason behind the reduction of kerf width, corner radius, and edge fillet radius in case of TVW, as indicated by the experimental observations, numerical simulations are performed. For a comparative study, current density distribution pattern over the workpiece surface is plotted for the three waveforms. Later, TVW is further optimized by varying its ‘rise’ and ‘fall’ time. For this, a factor termed as Pulse Rise Factor (PRF) is defined and is varied in 5 steps. Experimental results suggest that kerf width is minimum 55.4 μm when PRF is zero and is maximum 71.8 μm when PRF is one. In the end, different micro features are machined using the optimal machining conditions.

Precision electrochemical machining of tungsten micro-rods using wire electrochemical turning method

The novel wire electrochemical turning (WECT) method has been proposed to machine tungsten with neutral electrolyte and bipolar pulse current in the authors’ previous research. The influence of tool wear caused by the bipolar pulse current, which is needed to remove the oxide layer generated on tungsten surface when using a neutral electrolyte, was eliminated by the WECT method because the wire tool electrode was kept being wound during the machining process. In this paper, the influences of the most important process parameters, such as the kind of electrolyte, wire material, wire diameter, rotation speed of the workpiece rod, and frequency of the pulse voltage, were studied to understand the fundamental aspects of the WECT method and improve the machining efficiency of tungsten micro-rods. The experimental results showed that the NaCl electrolyte and the NaNO3 electrolyte had higher machining efficiency and better machining accuracy, respectively. The machining accuracy was improved with the SUS304 stainless steel wire used as tool electrode than the brass wire tool electrode. It was also found that the machining efficiency and accuracy were improved with decreasing the wire diameter and increasing the rotation speed of workpiece because the influence of stray current flowing through the side and end surface of machined micro-rod was reduced. The machinable length of micro-rod peaked at an optimum feed speed of the workpiece, and the optimum speed increased with increasing the frequency of pulse voltage. As a result, a minimum rod diameter of 11 μm was fabricated with a high aspect ratio of 36. Compared with the previous method using a platinum film as tool electrode, the aspect ratio was increased significantly because the influence of tool wear was eliminated.

Gas-water two-phase discharge phenomenon in PEF chamber for water treatment

Pulsed Electric Field treatment is a critical technology in waste water treatment and sterilization. However, the discharge of the treatment chamber that causes the damage of pulse generators is one of the main technical issues of its applications. Bubbles under water are the most vulnerable sections and could cause breakdown since it is too difficult to generate discharge in the bulk of water under microsecond-pulse and relatively low electric field(<70kV/cm). Uniform discharging images of gas bubbles under water are captured. The influence of γ approach on breakdown in short gas gap (under 1cm) with water electrode under atmospheric pressure is confirmed. The influence of conductivity of aqueous solution and the repetitive frequency of voltage pulses is discussed. It can be confirmed that the breakdown phenomenon of the PEF treatment chamber is mainly caused by air bubbles, which are generated by Joule heat process as well as cavitation and then discharge under the metal cathode. This work presents vital references for improving the design of PEF treatment chambers.

Reducing overcut in electrochemical micromachining process by altering the energy of voltage pulse using sinusoidal and triangular waveform

In electrochemical micromachining (ECMM), improved material dissolution localization and generation of the smooth machined surface under pulsed voltage condition is attributed to the fact that short pulse-duration time results in the generation of relatively less volume of dissolution products. The intermittent supply of voltage provides idle time to flush the hydrogen bubbles and sludge from the machining zone and, also increases control over the dissolution process. From the last few decades, various studies have been carried out to analyze the effect of short pulse voltage to ultra-short pulsed (rectangular) voltage. Development of such a sophisticated system capable of supplying ultra-high frequency voltage pulses is challenging, cost in-effective and complex. Also, the compromising ways of reducing the pulse energy by reducing the duty cycle and increasing the pulse frequency impose increased voltage requirement and idle time while machining. In this study, an approach of reducing pulse energy per unit time by changing the waveform of the voltage pulse (while keeping the pulse-duration time the same) for reducing the overcut is presented. A theoretical model is developed first to quantify the input energy per pulse for rectangular, sinusoidal, and triangular voltage pulses. This ensured that by changing the shape of voltage pulses of same on-time, the energy input per pulse can be further altered. A function generator based pulsed power supply is then developed with the capability of generating rectified voltage pulses of different waveforms. The process of ECMM for generating micro dimples on a flat surface is modeled in two dimensions using finite element method in MATLAB (R2018b). Three numerical models for sinusoidal, rectangular and triangular voltage pulses are developed for predicting the current density and anode shape. Simulation results demonstrated that triangular voltage pulse yields minimum diameter of micro-dimple as compared to sinusoidal and rectangular pulse respectively. Results from the developed model are also validated using experimental observations and a good correlation between the two was observed (with an average deviation of 18%).

A self-powered counter/timer based on a clock pointer-like frequency-tunable triboelectric nanogenerator for wind speed detecting

A self-powered technology is a promising approach to achieving sustainable power supply in large-scale wireless sensor networks. Here we report a clock pointer-like triboelectric nanogenerator (CP-TENG) with two non-contact tribo layers which can deliver an abrasion-free operation. The output voltage pulse frequency is tunable by subtly changing the number of electrodes that can improve output power density to some extent. Due to the one-to-one correspondence between voltage pulses and counting points, a self-powered counting and timing systems have been demonstrated via a programmable software platform. Furthermore, by integrating with a wind cup, a self-powered wind speed detector based on the CP-TENG indicates a superior real-time monitoring for wind speed attributed to accurately determining of algorithm parameter. This work not only pushes the development of self-powered systems, but also expands potential applications based on the TENG in intelligent interaction, environmental monitoring, industrial production and meteorological detecting.

Investigation of electrochemical micromachining of tungsten microtools

Tungsten tools are used in various advanced manufacturing industries owing to their excellent physical and mechanical properties. However, the material characteristics of tungsten, such as its hardness and brittleness, make it difficult to fabricate tungsten microtools using mechanical methods. Electrochemical micromachining (ECMM) is a potential method for machining tungsten microstructures, because the process is independent of the material physical and mechanical properties. In this paper, an investigation into ECMM of tungsten microtools using a rotary helical electrode is presented. The optimal process conditions, including electrolyte concentration, duty ratio, and frequency of pulsed voltage, are determined experimentally. A quantitative relation between the machining side gap and the applied voltage and electrode feed rate, which can be controlled online during the machining process, is calculated from the experimental results. A contour map is drawn to aid in selecting the optimum process parameters to achieve a specific slit width. Finally, a tungsten array microtool with variable cross-section is fabricated by adjusting the applied voltage online.

Trap distribution of electron beam irradiated epoxy resin under repetitive pulse voltage

Epoxy resin has been widely used as dielectric material in irradiation environment, such as nuclear power plants, aerospace equipment and superconducting power apparatus. This paper investigated the effects of different electron beam irradiation doses on the trap distribution of epoxy resin under repetitive pulse voltage. Samples were irradiated at room temperature (20 °C) in air by high energy electron beam of 7.5 MeV with beam density ranging from 0.35 to 0.45 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The total irradiation dose was 0, 100, 500 and 700 kGy, respectively. The corona charging was performed under ± 6 kV pulse voltage with different pulse frequencies in atmospheric air with relative humidity of 20%. The surface potential was collected through an electrostatic voltmeter to obtain the trap distribution at room temperature, and the isothermal discharge current of the samples processed with different irradiation dose was measured to calculate the trap distribution in liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The experimental results indicate that both at room temperature and in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the trap level decreases first and then increases with the increase of irradiation dose. The trap level and the trap density have the positive correlation with pulse voltage frequency. At room temperature, the electron traps have higher energy level and deep trap density, but have lower shallow trap density than the positive charge traps.

Effect of the voltage pulse frequency on the structure of TiO2 coatings grown by plasma electrolytic oxidation

Plasma Electrolytic Oxidation (PEO) is used to synthetize titanium dioxide (TiO2) ceramic coatings with the appropriate selection of an electrolyte. The dimension of the micro-cavities and the particle size at the surface can be controlled through the pulse frequency of the voltage that is applied between the electrodes. The change of surface morphology can increase the surface area-to-volume ratio. In this work, PEO of an ASME SB-265 titanium substrate (20×20×1mm) was made in a water solution containing 8g/L Na3PO4 and 0.4g/L NaOH. Hence, the coatings were fabricated using voltage pulses of 340V for 10 minutes with a 10% duty cycle and frequencies of 1000, 1500 and 2000Hz. According to the X-ray diffractograms of the obtained samples, the sintering process at 500°C during 1 hour generated Anatase titanium dioxide porous coatings. The grain size decreased approximately from 29nm for 1000 and 1500Hz pulse frequencies until 21nm for 2000Hz. On the other hand, from the micrographs of scanning electron microscopy was possible to see the uniform formation of the micro-cavities with the largest diameter, 900nm, for the lowest frequency value used in PEO.

Simulation Research on the Digital Servo Drive System for the Large Inertia and DC Torque Motor

To solve the problem of the speed stability on the digital servo drive system for the large inertia and DC torque motor and improve the system’s performance and reliability, the research on control strategy is conducted. Based on the working characteristics of the radar turntable DC torque motor servo system, the three PWM control modes on the H-bridge power main circuit and the current pulsating quantity and direct connection on uni-polar control mode are analyzed; by improving the pulse voltage frequency on the armature’s ends, the system’s performance is improved. The system’s mathematical model is established, the system is simulated by using the transfer function in the MATLAB/SIMULINK and analyzed in the qualitative method.

Flow-Through Electroporation of HL-60 White Blood Cell Suspensions using Nanoporous Membrane Electrodes.

A flow-through electroporation system, based on a novel nanoporous membrane/electrode design, for the delivery of cell wall-impermeant molecules into model leukocytes, HL-60 promyelocytes, was demonstrated. The ability to apply low voltages to cell populations, with nm-scale concentrated electric field in a periodic array, contributes to high cell viability. With applied biases of 1-4V, delivery of target molecules was achieved with 90% viability and up to 65% transfection efficiency. More importantly, the system allowed electrophoretic pumping of molecules from a microscale reservoir across the membrane/electrode system into a microfluidic flow channel for transfection of cells, a design that can reduce reagent amount by eightfold compared to current strategies. The flow-through system, which forces intimate membrane/electrode contact by using a 10μm channel height, can be easily scaled-up by adjusting the microfluidic channel geometry and/or the applied voltage pulse frequency to control cell residence times at the cell membrane/electrode interface. The demonstrated system shows promise in clinical applications where low-cost, high cell viability and high volume transfection methods are needed without the risk of viral vectors. In particular genetic modification of freely mobile white blood cells to either target disease cells or to express desired protein/enzyme biomolecules is an important target platform enabled by this device system.

Electrochemical micromachining of microchannel using optimum scan feed rate

Electrochemical micro-micromachining (EMM) is the key to micro-machining technology for the manufacturing of micro size, complex shaped components and micro profiles. The research reported in this paper aims at reducing the overcut, taper angle, end deviation, deviation along the edges of microchannel and improved surface finish. In the present research, emphasis has been given to formulation and calculation of scan feed rate at different settings of parameters. Theoretical scan feed rate is calculated based on derived formula and compared with optimum scan speed based on experimental trial run. Optimum scan speed rate will be very much useful for EMM of electrically conductive material for the generation of microchannel with reduced overcut and without damage of microtool as well as the machined surface area due to disturbance of short circuit caused by contact between anodic work piece and cathode microtool. The reason for sedimentation at the edges is also analyzed in detail. The major process parameters investigated are applied voltage, electrolyte concentration, microtool feed rate along the path, downward speed of feed, frequency of pulsed voltage, frequency of vibration of microtool and amplitude of vibration of microtool. It has been found that overcut as well as time of machining is least in 0.2M H2SO4 electrolyte for taper less through micro-channel machining. Surface finish improves with increase in concentration i.e. Ra value decreases in a parabolic manner with increase in concentration. With the introduction of low amplitude microtool vibration of 0.3μm, surface finish further improves without excess overcut and also, avoids metal ions sedimentation at the edges of microchannel.

Effect of pulse frequency on tree characteristics in epoxy resin under low temperature

The superconducting magnet system is the key part of international thermonuclear experimental reactor (ITER) device which has attracted much attention in many countries. Due to its excellent performance in many aspects, epoxy resin has been selected as the base material of superconducting magnet insulation. Considering the unique operating environment, epoxy resin faces the challenge of liquid helium temperature as well as pulse voltage. The influence of pulse frequency and polarity on the electrical tree characteristics in epoxy resin under low temperature is investigated in this paper. Samples made of epoxy resin were stressed with the different frequencies in the needle-plate geometry electrodes. The frequency of pulse voltage varied from 100 to 500 Hz with positive and negative polarities. The experimental temperature was set to -30, -90 and -196 °C. Accumulated damage and expansion coefficient (D/L) are employed to characterize the electrical tree. The experimental results indicate that low temperature, pulse frequency and polarity have an influence on treeing process. The typical tree structures in epoxy resin are obviously different with the variation of low temperature and pulse frequency. It is revealed that the low temperature is resistant to the growth of electrical tree and there are more small branches generating from the main branches with the decrease of temperature. However, when under the same low temperature, the tree initiation and propagation processes are accelerated by the higher pulse frequency. The density of the tree branches increases with the increase of pulse frequency. The accumulated damage presents a similar trend corresponding to branches density. Meanwhile, electrical tree tends to grow faster with the positive pulse than negative pulse under the low temperature. Moreover, the higher value of D/L at lower temperature implies that tree branches extend at a wide range direction.

Vibration assisted electrochemical micromachining of high aspect ratio micro features

The most used processes for generation of high aspect ratio microchannels are Nd: YAG laser technology on silica substrate and ultra violate lithography (UV-LIGA) process on metals. There are a few micromachining technologies such as micro mechanical milling, micro electro discharge machining (EDM) and electrochemical micromachining (EMM) for production of high-aspect-ratio micro features on highly stressed and anticorrosive metal like stainless steel. This paper discusses the micro fabrication of high aspect ratio micro features at the intended location on high strength stainless steel sheet of very small thickness to high thickness with highest average aspect ratio 14.33 achieved during microchannel generation by EMM with the help of coated microtool. Mathematical model relating aspect ratio with various parameters and machining conditions is derived to explore the ways to increase the aspect ratio of micro features. Experimental investigations were carried out to know the effect of vibration of microtool, frequency of pulsed voltage, microtool tip shape, thickness of work piece and non-conducting layer coated microtool on high aspect ratio micro features. Vibration of microtool with very small amplitude improved the stability of micromachining due to improved flow of electrolyte.

On the homogeneity of a diffuse barrier discharge in atmospheric air between flat cylindrical electrodes

The degree of homogeneity of a diffuse dielectric barrier discharge in millimeter air gaps under atmospheric pressure has been analyzed. This analysis is based on the glow-brightness distribution in the discharge gap cross section with allowance for a cylindrical electrode shape. It is shown that the degree of discharge homogeneity depends on both the repetition frequency of voltage pulses applied to the discharge gap and the barrier material.

Electrical tree characteristics in silicone rubber under repetitive pulse voltage

Electrical tree in silicone rubber (SiR) is a threat to the power system. Bedsides ac and dc voltage, there are pulse voltage in power system and the electrical tree behavior in SiR under pulse voltage has not been reported. In this paper, electrical treeing process in SiR under pulse voltage was investigated and analyzed. The voltage was applied to a needle-plate electrode to initiate electrical trees. The frequency of pulse voltage was 100, 200 and 300 Hz and the amplitude ranges from 8 to 14 kV. Aspects such as the patterns of electrical tree, tree length, accumulated damage, fractal dimension and tree breakdown characteristics were studied. Results indicate that the pulse amplitude plays the leading role in electrical tree initiation, propagation and breakdown processes. With the increase of pulse amplitude, the tree structure changes and the breakdown possibility increases obviously. However, the tree length is not sensitive to pulse frequency and higher pulse frequency promotes the increase of tree density. It also has been found that tree structure is closely related to pulse polarity and the inception voltage is lower with positive pulse than that with negative.

Quantum tomography of an electron.

The complete knowledge of a quantum state allows the prediction of the probability of all possible measurement outcomes, a crucial step in quantum mechanics. It can be provided by tomographic methods which have been applied to atomic, molecular, spin and photonic states. For optical or microwave photons, standard tomography is obtained by mixing the unknown state with a large-amplitude coherent photon field. However, for fermions such as electrons in condensed matter, this approach is not applicable because fermionic fields are limited to small amplitudes (at most one particle per state), and so far no determination of an electron wavefunction has been made. Recent proposals involving quantum conductors suggest that the wavefunction can be obtained by measuring the time-dependent current of electronic wave interferometers or the current noise of electronic Hanbury-Brown/Twiss interferometers. Here we show that such measurements are possible despite the extreme noise sensitivity required, and present the reconstructed wavefunction quasi-probability, or Wigner distribution function, of single electrons injected into a ballistic conductor. Many identical electrons are prepared in well-controlled quantum states called levitons by repeatedly applying Lorentzian voltage pulses to a contact on the conductor. After passing through an electron beam splitter, the levitons are mixed with a weak-amplitude fermionic field formed by a coherent superposition of electron-hole pairs generated by a small alternating current with a frequency that is a multiple of the voltage pulse frequency. Antibunching of the electrons and holes with the levitons at the beam splitter changes the leviton partition statistics, and the noise variations provide the energy density matrix elements of the levitons. This demonstration of quantum tomography makes the developing field of electron quantum optics with ballistic conductors a new test-bed for quantum information with fermions. These results may find direct application in probing the entanglement of electron flying quantum bits, electron decoherence and electron interactions. They could also be applied to cold fermionic (or spin-1/2) atoms.