Voltage Pulse Frequency Research Articles

Pulsed voltage enhanced electro-dewatering of sewage sludge: A comparison between pulsed and constant voltage

Electro-dewatering (EDW) of sewage sludge was conducted to investigate the effect of pulsed voltage on EDW performance by comparing it with constant voltage. A pulsed voltage with constant amplitude of 50 V was applied on top of different base voltages (10, 20, or 30 V). The frequency of pulsed voltage was set at 10 Hz to investigate the effect of duty cycle (2%, 5%, 10%, and 20%) on the EDW performance. The results showed that, under the same average voltage, the water content of the dewatered sludge was 0.63% to 4.03% lower under pulse voltage conditions compared to constant voltage conditions, indicating that pulse voltage could enhance EDW performance. Transmission electron microscopy analysis of sludge cells revealed that pulsed voltage was more effective in breaking sludge cells than constant voltage. This resulted in increased release of bound water and a reduction in sludge cake resistance, which is a key reason why pulsed voltage outperforms constant voltage in EDW. The energy consumption of EDW ranged from 0.088 kW·h to 0.381 kW·h per kilogram of removed water. The energy consumption for pulsed voltage at the base voltage of 30 V was about 2%–7% lower than that of constant voltage, while the energy consumption under the lower base voltage (10 V and 20 V) was almost equal to that of constant voltage conditions. Considering both energy consumption and EDW performance, the optimal duty cycle was 5% for a base voltage of 10 V, and 2% for base voltages of 20 V and 30 V. These findings laid theoretical foundation for future application of EDW with pulse voltage.

ВЛИЯНИЕ ЧАСТОТЫ СЛЕДОВАНИЯ ИМПУЛЬСОВ НА ФОРМИРОВАНИЕ ПЛАЗМЕННЫХ ДИФФУЗНЫХ СТРУЙ ПРИ ДАВЛЕНИИ ВОЗДУХА 1 ТОРР

The influence of the repetition rate of voltage pulses on the formation of plasma diffuse jets (PDJs) initiated by a capacitive discharge at an air pressure of 1 Torr has been studied. The PDJs were photographed at different frequencies and polarities of generator voltage pulses and emission spectra were recorded in the UV, visible, and IR regions of the spectrum. It has been shown that a decrease in the frequency of voltage pulses at negative polarity increases the ratio of the spectral energy density of radiation of the first positive nitrogen system to that of the second one, which contributes to an increase in the intensity of radiation in the red region of the spectrum. It has been established that a decrease in the repetition rate of voltage pulses contributes to the formation of two peaks at the front of the current pulse. The conducted studies confirm that PDJs can be considered analogous to columnar red sprites and their properties can be modeled.

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

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

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

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

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

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

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

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

Investigation of electrochemical micromachining of tungsten microtools

Investigation of electrochemical micromachining of tungsten microtools

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 micromachining of microchannel using optimum scan feed rate

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

Vibration assisted electrochemical micromachining of high aspect ratio micro features

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.