Unipolar Pulse Voltage Research Articles

Effect of Pulse Conditions on Machining Characteristics in Bipolar-Pulse Electrochemical Machining of Cemented Carbide

Electrochemical machining was performed on two cemented carbides with different compositions using unipolar and bipolar short-pulse voltages to investigate the effects of the composition and pulse conditions on the machining characteristics. In the case of cemented carbides with high cobalt and low tungsten carbide (WC) contents, machining progressed even when a unipolar voltage was used. This is believed to be due to the dissolution of the binder, that is, Co, which causes the WC and WO3 particles to drop out. Machining progressed more easily when a bipolar voltage was used than when a unipolar voltage was used. This is attributed to the effective removal of WO3. The unevenness of the machined surface was also reduced with bipolar voltage. The negative pulse duration had to be sufficiently but appropriately long, because too long a duration increased the wear of the tool electrode. Even when bipolar pulse voltages were used, similar to the machining of general materials, a shorter positive pulse duration resulted in more precise machining. However, in the case of cemented carbide with low Co and high WC contents, the removal did not progress when a unipolar pulse voltage was applied. On the other hand, the machining progressed when a bipolar voltage was applied. However, if the positive pulse duration was excessively long, the amount of removal decreased. This is believed to be because the longer positive pulse duration increased the amount of WO3 generated, thereby inhibiting the current flow. Therefore, it is necessary to set an appropriate positive pulse duration to avoid the excessive production of WO3.

Discharge Characteristics and Mechanism of Bubble Flow in FC-72 under Unipolar Repetitive Pulse Voltage

This article investigates the discharge characteristic of the bubble flow in FC-72 under unipolar repetitive pulsed voltage, which supports the insulation design of two-phase cooling in an HV power electronic device. The effect of thermal bubble flow on the insulation of FC-72 refrigerant was evaluated. According to the partial discharge (PD) characteristics, it is found that there are two stages in the discharge characteristics of the bubble flow as voltage rises. Combining the PD inception voltages of FC-72 vapor under unipolar pulse voltage and dc voltage, it reveals the discharge thresholds of the vapor inside the bubble under the transient electric field and the steady electric filed, respectively, which proves the mechanism of the staged PD evolution. Based on the motion calculation of the bubble, the PD probability of the bubble flow within a voltage period is analyzed. It simulates the phase-resolved PD pattern, which reveals the PD mechanism of the bubble flow. The research provides a reference for the insulation design for the two-phase cooling technology in power electronics.

Inactivation of bacteria suspended in water by using high frequency unipolar pulse voltage

AbstractFood processing by pulsed electric field has received considerable attention in food and biotechnology. Although the PEF technology for bacterial inactivation depends upon both biological factors and electrical parameters, this article mainly focuses on the impact of pulse repetitive frequency on the bacterial inactivation suspended in liquid. This research work also aims to implement compact pulse converter technology using power MOSFETs to generate 1.5 kV unipolar pulses of width 1.2 μs at different pulse repetition frequency. The efficacy of the pulse generator was tested to inactivate Escherichia Coli MTCC 1610 strain suspended in water at 1, 10, 20, and 51 kHz at 15 kV/cm. It was observed that maximum of 4.4 log10 reduction of bacteria was achieved at 51 kHz (with 1,530,000 pulses) and about 1.2 log10 reduction achieved at 1 kHz (with 30,000 pulses). It shows that high repetitive frequency has significant impact on the process to inactivate the bacteria at moderate electric field intensity.Practical applicationsFrom the literature, it can be stated that the efficiency of inactivation process is determined by the amplitude of the pulsed electric field intensity. Ultimately this concept increases the cost of the PEF generator and complexity in circuit design. So, this work concentrates to bring down the electric field intensity without sacrificing the efficiency of the process by altering the pulse repetitive frequency among all other electrical parameters. The research also focuses to implement a bench scale PEF to inactivate bacteria in liquid food. The advancements in power semiconductor devices may help to improve the design of PEF generators and the developed PEF converter generates unipolar pulses of 1.5 kV at a variable frequency of 1 kHz to a maximum of 51 kHz with help of simple programmable microcontroller. This bench scale PEF converter is very compact. Since the pulse repetition frequency shows the significant log reduction, this helps to reduce the capital investment and has more options to scale up the design in pulsed power technology. With better power generators, after decades of research, PEF technology may finally be commercialized to inactivate bacteria.

Electrical Stimulation of NIH-3T3 Cells with Platinum-PEDOT-Electrodes Integrated in a Bioreactor

The objective of this work involves the development and integration of electrodes for the electrical stimulation of cells within a bioreactor. Electrodes need to fit properties such as biocompatibility, large reversible charge transfer and high flexibility in view of their future application as implants on the tympanic membrane. Flexible thin-film platinum-poly(3,4-ethylene-dioxythiophene)-electrodes on a poly(ethylene terephthalate)-foil manufactured using microsystems technology were integrated into a bioreactor based on the design of a 24 well plate. The murine fibroblast cell line NIH-3T3 was cultured on the foil electrodes and the cells were stimulated with direct voltage and unipolar pulsed voltage. The amplitude, the pulse length and the ratio of pulse to pause were varied. The stimulated cells were stained in order to determine the angle between the cell cleavage plane of the dividing cells and the vector of the electric field. These angles were subsequently used to calculate the polarization index, which is a measure of the orientation of the metaphase plane of dividing cells that occurs for example during wound healing or embryonic morphogenesis.

Analysis of Power in an Argon Filled Pulsed Dielectric Barrier Discharge

In this paper an argon filled coaxial dielectric barrier discharge (DBD) has been studied to understand the detail of power transfer from a unipolar square pulse to plasma during discharge. A dielectric barrier discharge based diffuse pulse discharge and its electrical characteristics are investigated. A quartz coaxial DBD tube filled at different pressures is used in the experiment. A unipolar pulse voltage of different peak voltages and frequencies has been applied to the discharge electrodes for the generation of microdischarges. Two current pulses are used for two consecutive discharges per applied voltage pulse. The second discharge, which occurs at the falling flank of the voltage pulse, is induced by the charges stored on the dielectric barrier during the first discharge. It has been deduced that the power supplied to ignite the first discharge is partly stored to ignite the second discharge when the applied voltage decays. This process ultimately leads to much improved power transfer to the plasma. The knowledge obtained from dynamic processes of the DBDs in the discharge gap explains quantitatively the mechanism of ignition, development and extinction of the DBDs.

Characterization of Vacuum Ultraviolet (VUV) Radiation for the Development of a Fluorescent Lamp

A negative unipolar pulsed voltage is applied to study internal electrical parameters of the xenon filled dielectric barrier discharge (DBD) sources. The VUV radiation emitted from these sources is characterized by means of the photoluminescence intensity of the red phosphor pellet. The red phosphor converts the VUV radiation into visible radiation and the emission spectra include a peak at 619.56 nm. The emission characteristics of the red phosphor are analyzed in terms of the pressure-distance (pd), rise time and frequency of the pulsed voltage waveform. The emission intensity measured at different operational conditions confirms that the formation and decay of the xenon excimer, Xe2*, increase with the increase in reduced electric field, E/N. After exceeding certain limits of E/N, the intensity of Xe2* decreases rapidly.

The Degradation of Thin Silicon Dioxide Films Subjected to Pulse Voltage Stresses at Nanoscale

In this paper, we report the observation of the degradation and breakdown of thin silicon dioxide films subjected to both the unipolar and bipolar pulse voltage stresses at nanoscale by using conductive atomic force microscopy. It is found that the unipolar pulse voltage stress produces more severe damage than does the bipolar pulse voltage stress. We also notice that hard breakdown is always preceded by soft breakdown for thin silicon dioxide subjected to either unipolar or bipolar pulse voltage stress, and the soft breakdown is always accompanied with random current fluctuation in the I-t characteristics. The influence of varying frequency of the pulse voltage stresses on the oxide breakdown is also investigated in this work.

Charge Trapping Characteristics of TaYOx Gate Dielectrics on Ge under DC and AC Stressing

TaYOx gate dielectric has been deposited on p-Ge by RF co-sputtering of Ta2O5 and Y2O3 targets. Charge trapping/detrapping behavior of Au/TaYOx/p-Ge MIS capacitors have been studied under DC and AC stressing of different amplitudes and dynamic voltage stresses in order to study the transient response and the degradation mechanism of the dielectric. The current transients observed during dynamic voltage stress have been interpreted in terms of the charging/discharging of Ge/TaYOx interface and bulk TaYOx traps. The change in Vfb and gate current during unipolar pulse voltage stressing shows that the main degradation takes place at low frequencies. Both types of trapping are observed under dynamic stressing both with the gate and substrate injections.

Experimental study on repetitive unipolar nanosecond-pulse dielectric barrier discharge in air at atmospheric pressure

Dielectric barrier discharge (DBD) is a typical approach for producing non-thermal plasma at atmospheric pressure. In this experimental study, the DBD is excited by repetitive unipolar nanosecond pulses with a rise time of ∼15 ns and a full-width at half-maximum of ∼30 ns. With a unipolar pulse voltage of 35 kV, the measured discharge current across the DBD circuit has a positive and negative pulse, and the pulse peak value can be hundreds of amperes. The low-speed camera images of the discharge show that both diffuse ‘glow-like’ and filamentary discharges can be observed, and the air gap length, barrier variety and applied repetition rate are the important factors influencing the transition of the two discharge modes. According to a known equivalent circuit and measured data of a typical DBD, electrical parameters including voltage, current and instantaneous power across the air gap and dielectric layer are calculated. The calculated results indicate that there are two consecutive discharges in the air gap, and the secondary discharge fires immediately after the primary discharge extinguishes. The power consumption of the secondary discharge is provided by the dielectric layer and deposited during the primary discharge. With the increase in the repetition rate, the energy deposition in the air gap per second is greatly enhanced and can exceed one joule for a repetition rate up to 100 Hz, and the corresponding charge transfer is also increased. The electron temperature and density are estimated to be approximately 5.1 eV and 1.6 × 1012 cm−3, respectively.

Reliability assessment of SiO 2/ZrO 2 stack gate dielectric on strained-Si/Si 0.8Ge 0.2 heterolayers under dynamic and AC stress

The reliability characteristics of SiO 2/ZrO 2 gate dielectric stacks on strained-Si/Si 0.8Ge 0.2 have been investigated under dynamic and pulsed voltage stresses of different amplitude and frequency in order to analyze the transient response and the degradation of oxide as a function of stress parameters. The current transients observed in dynamic voltage stresses have been interpreted in terms of the charging/discharging of interface and bulk traps. The evolution of the current during unipolar pulsed voltage stresses shows the degradation being much faster at low frequencies than at high frequencies. Results have been compared with those obtained after CVS, as a function of injected charge and pulse frequency.

Enhanced electrokinetic remediation of metals-contaminated clay

Analysis of polarization processes at electrokinetic remediation of clay soils and evaluation of the contribution of various components into the transport of charged contaminants are performed. The peculiarities of soil decontamination at constant and pulse voltages are investigated using kaolinite and mixture of montmorillonite and sand contaminated with radionuclides ( 137Cs, 90Sr, U) and heavy metals (Co) as model systems. It is shown that the use of unipolar pulse voltage changes the distribution of contaminations in soil and allows to decrease power inputs. It is also demonstrated that the introduction of cation-exchangers CU-2-8 into electrode chambers considerably improves the degree of soil decontamination. The most effective method to intensify the decontamination of clay soils from radionuclides and heavy metals is the wetting of soil with enhancement reagents (acetic, nitrilotriacetic and ethylenediaminetetraacetic acid).

Study of unipolar pulsed ramp and combined ramped/constant voltage stress on mos gate oxides

MOS gate oxide capacitors over a wide range of oxide thicknesses (10.9–28 nm) were stressed using a unipolar pulsed voltage ramp and combined ramped/constant voltage stress measurements. The reliability measurements were performed with several different bias conditions in order to assess the effects of the measurement conditions on times to breakdown and breakdown fields. In the first part it was verified that the unipolar pulsed ramp yields breakdown distributions which are identical to those of a widely used staircase ramp. In the second part the unipolar pulsed ramp was used for pre-stress prior to a constant stress and measurement results were compared to those of a ramped/constant stress with a staircase ramp. In several cases a ramp prior to a constant stress increases time to breakdown. The observations made in this study imply that the time to breakdown of a constant stress in the Fowler-Nordheim tunneling regime is strongly dependent on charge trapping and, therefore, on the stressing history of the oxide. Finally, it is shown that the combined ramped/constant voltage stress is a valuable tool for monitoring extrinsic and intrinsic breakdown properties when applying stress parameters in the correct way.