Unipolar Voltage Pulses Research Articles

Study on powering electric filters with unipolar high voltage pulses

The article presents the devices of existing power supplies for electrical engineering installations and analyzes their disadvantages. The necessity of developing a method for stabilizing discharge processes in corona discharge electric fields is formulated. The calculation of the transient process in the pause between pulses when powered by unipolar high-voltage pulses with a duty cycle of more than 5 is carried out and the conditions under which the discharge currents are stable are determined. A source with two-way power supply and air cooling has been developed to supply electric filters with unipolar high-voltage pulses. The schematic diagram of the source of periodic voltage pulses, the parameters of the circuit elements, the device of the step-up transformer, the oscillogram of the voltage at the output of the generator and the type of voltage at the output of the source are given.

Neural network search for optimal pulse trains for qubit dynamics control

Despite its insensitivity to charge noise, the transmon's anharmonicity and control pulse length are limited. Transmon state control traditionally involves a quadrature mixer that mixes microwave signals from a room-temperature oscillator and an arbitrary waveform generator to control the single qubit states. Scaling upquan tum processors faces challenges in hardware, management of qubit operations, and read-out procedure due to the large amount of expensive room-temperature equipment required for each qubit. Operating at millikelvin temperatures, these devices introduce thermal noise, reducing qubit lifetime and distorting control signals. An alternative promising control method is based on superconducting digital electronics. In these digital circuits, a bit of information is represented by a short unipolar voltage pulse generated when a single flux quantum (SFQ) pulse passes through a Josephson junction. The qubit states are controlled by the action of a sequence of SFQ pulses, with the pulse-to-pulse timing adjusted to induce a coherent rotation of the state vector in the computational subspace and to minimize leakage to the outside. The paper discusses a method for controlling the states of a transmon qubit using digital superconducting electronics. In this approach, the sequences of picosecond voltage pulses are used to control the state of a quantum computing system. We have considered a control scheme based on a bipolar pulse generator and proposed an algorithm for finding the optimal implementation of a bipolar short pulse control sequence for performing high-precision single-bit operations (with fidelity equal to 99,99 %) using deep learning algorithms with rein forcement: AlphaGo Zero, AlphaZero and Proximal Policy.

A Solid-State Bipolar Pulse Power Generator for Dielectric Barrier Discharge Applications

This article provides a distinctive unipolar/bipolar high voltage pulse power generator (PPG) architecture that produces exponential waveform with a rise time in the range of nanosecond. The setup is fit for dielectric barrier discharge applications, in practice. In this work, a push-pull circuit with a three-winding transformer is utilized on the charging side, as well as a quasi-resonant between the transformer leakage inductance and the capacitor on the discharging side to boost the voltage gain. As a result of the two windings on the primary side, and the bidirectional switches on the high voltage side, the tool offers either unipolar or bipolar high voltage pulses from a relatively low dc source. In addition to accomplishing the high gain objective, the effort focuses on lowering the number of circuit elements in contrast to previously studied topologies. The generator functions in discontinuous conduction mode, which enhances system efficiency by allowing complete positive and/or negative waves to be generated while lessening conduction losses. The pulse generator operation intervals are described in depth. The simulation results will demonstrate how this topology outperforms the prior models. Moreover, a 1000-V experimental prototype is also implemented to validate the projected PPG-enhanced properties in real-time.

Experimental comparison of partial discharge between fast-switching pulse waves and square waves

The behaviour of partial discharge has been examined for unipolar turn-to-turn-like waveforms with short 10%–90% rise-times of approximately 25 ns. Such waveforms simulate what may be seen between turns on random-wound inverter-fed electrical machines driven by ultra-fast switching wide-bandgap power semiconductors. The influence of pressure, voltage polarity, and pulse duration was examined, with particular focus on environments relevant to aerospace. Pulse waves were observed to generate distinct partial discharge behaviour relative to square waves, with important implications for detection and lifetime assessment. Partial discharge likelihood for pulse waves at a given voltage was reduced, with comparable discharge activity requiring an additional several hundred volts at both ambient pressure and 116 hPa. Partial discharge events typically occur sooner after voltage rise for shorter duration pulses, whereas discharges occasionally occurred over 1 ms after voltage rise for longer-duration 10–100 Hz square waves at lower pressures, which may be outside the window of detection of some instrumentation. While observations and stochastic behaviour were interpreted within the context of space charge and the latest understanding of Volume-Time theory, some observations have not been able to be accounted for. These include observed stochastic trends between partial discharge delay time and unipolar pulse duration not correlating well, a reduced delay between voltage change and partial discharge activity during voltage fall relative to rise, and the lack of observed partial discharge activity after voltage fall for unipolar voltage pulse durations less than 50 µs.

Recent progress in random number generator using voltage pulse-induced switching of nano-magnet: A perspective

Voltage pulse-driven switching of nano-magnets has gained distinct attention because of its high-speed writing with ultralow power consumption. One of the key advantages is that the external voltage applied to a nano-magnet reduces the magnetic anisotropy energy and excites a precessional motion of magnetization. By adjusting the duration and amplitude of the voltage pulse, a switching probability close to 50% can be attained, suggesting that the magnetic state of nano-magnets can be used as a source for generating binary random numbers (RNs) in principle. Because the bi-directional switching of nano-magnets is induced by unipolar voltage pulses, which is essentially different from the case of spin transfer torque (STT) switching, the results are a mixture of two switching polarities: from parallel (“0” state) to antiparallel (“1” state) and vice versa. Here, we focus our attention on the appearance probabilities of four cases, “00,” “01,” “10,” and “11,” all of which change linearly as functions of voltage. By tuning the probabilities of “00” or “11” to 25%, well-balanced RNs can be generated. A clear advantage of the voltage-pulse driven random number generator (RNG) over the conventional STT-driven one is lower consumption, which enables integration and heavily parallel operations of a large number of RNGs.

Experimental and Numerical Study of Electroporation Induced by Long Monopolar and Short Bipolar Pulses on Realistic 3D Irregularly Shaped Cells.

In this article, the reversible electroporation induced by rectangular long unipolar and short bipolar voltage pulses on 3D cells is studied. The cell geometry was reconstructed from 3D images of real cells obtained using the confocal microscopy technique. A numerical model based on the Maxwell and the asymptotic Smoluchowski equations has been developed to calculate the induced transmembrane voltage and pore density on the plasma membrane of real cells exposed to the pulsed electric field. Moreover, in the case of the high-frequency pulses, the dielectric dispersion of plasma membranes has been taken into account using the second-order Debye-based relationship. Several numerical simulations were performed and we obtained suitable agreement between the numerical and experimental results.

IMPROVING THE EFFICIENCY OF ELECTROSTATIC PRECIPITATORS

This paper provides information on the achievements in development of gas cleaning. A critical analysis of functioning principle of electrostatic precipitators, which are currently being developed and operated, is conducted. The possibility of increasing the effectiveness of gas cleaning using unipolar voltage pulses has been analyzed. It has been found that a streamer mechanism of discharge or streamer shape of corona discharge is the case, when voltage pulses with over-voltage are used and electrostatic precipitators run. The most rational circuit for unipolar voltage pulses generation using low-voltage generators of periodic voltage pulses is identified. To separate space charges formed in the streamers' channel, it is proposed to use pulsating voltage with a direct component and a potential plane with corona needles-grounded plane electrode system. The analysis of transient process within feed circuit of discharge technological gaps has shown that cut-off pulse repetition frequency, in which stability of discharge current is ensured, depends on the parameters of feed circuit elements and the discharge gap capacitance. It was found that the use of corona discharge streamer form allows increasing the speed of the gas to be purified up to 8 m/s, and reducing the aerosol particles deposition zone to 1 m. The gas velocity is 1 m/s with a deposition zone of more than 27 m in an existing gas filling device (GFD) type electrostatic precipitator. When comparing these indicators, the energy intensity of the process decreases by more than 100 times, and the specific power of the gas flow purification process is 33 (W·s)/m3.

Modes of Impulse Barrier Discharge to Water Surface in Atmospheric Air

The possibilities of creating a homogeneous discharge in air of atmospheric pressure between a flat metallic electrode covered by a dielectric barrier and water surface are demonstrated. In the experiments, the discharge was initiated in the gas gaps by applying unipolar voltage pulses with fronts of ~15 ns and duration of ~100 ns. It was found that the discharge mode was affected by the pulse repetition rate. Its critical magnitude corresponding to the appearance of a homogeneous discharge was reduced from 500 to 50 s−1 if the length of the air gap was increased from 1 to 4 mm. The lifetime of a homogeneous discharge mode was affected by the total duration of the discharge. Thus, it was about several tens of seconds at a pulse repetition frequency of 100 s−1 and it reduced at increased frequencies. It is suggested that the transition from homogeneous to inhomogeneous modes is associated with local overheating of the gas due to significant energy dissipation in the discharge volume.

Effects of dielectric properties on electrical characteristics of dielectric barrier discharge generated by low frequency uni-polar high voltage pulses

This paper presents experimental results concerning the effects of properties of glass and ceramic dielectric on electrical characteristics of the dielectric barrier discharge (DBD). The effect has been examined with a focus on low frequency uni-polar pulse driving in order to eliminate influences induced by the presence of residual charges and mestastable states in the discharge volume. The results revealed that at low frequency, in the glass reactor, the discharge just occurred after a delay with respect to moment when a high voltage pulse is applied to the reactor, whereas this phenomenon was not observed in the case of discharge in the ceramic reactor. Furthermore, in the glass reactor, DBD was generated with a much higher current peak and shorter discharge current duration in comparison with the electrical characteristics of DBD generated in a ceramic reactor. The differences are presumed to be the result of the difference in ability of trapping and binding surface electrons of dielectric layers.

Skyrmion-Mediated Voltage-Controlled Switching of Ferromagnets for Reliable and Energy-Efficient Two-Terminal Memory.

We propose a two-terminal nanomagnetic memory element based on magnetization reversal of a perpendicularly magnetized nanomagnet employing a unipolar voltage pulse that modifies the perpendicular anisotropy of the system. Our work demonstrates that the presence of Dzyaloshinskii-Moriya interaction can create an alternative route for magnetization reversal that obviates the need for utilizing precessional magnetization dynamics as well as a bias magnetic field that are employed in traditional voltage control of magnetic anisotropy (VCMA)-based switching of perpendicular magnetization. We show with extensive micromagnetic simulation, in the presence of thermal noise, that the proposed skyrmion-mediated VCMA switching mechanism is robust at room temperature leading to extremely low error switching while also being potentially 1-2 orders of magnitude more energy efficient than state-of-the-art spin transfer torque-based switching.

Diagnostics of the thickness of a plasma electrolytic oxidation coating on a nanostructured Mg-Sr alloy

This study is focused on the development of a method for controlling the thickness of a plasma electrolytic oxidation (PEO) coating on a new nanostructured Mg-2wt%Sr alloy. The process of high pressure torsion of a solution-treated Mg-2wt%Sr magnesium alloy was investigated. A significant reduction in the grain size to 500 nm was attained. The PEO coating process on the new nanostructured Mg-2wt%Sr alloy was studied. The produced coating was compared with a PEO coating with a coarse-grained structure. The waveforms of unipolar voltage pulses of a power source were studied, and electrical transients that can be described by an exponential of the second order were revealed. The relationship between the time constant of the electrical transient exponent and the thickness of the PEO coating was justified. A method for estimating the thickness of the PEO coating on the surface of the Mg-2wt%Sr alloy in terms of the parameters of the electric transient was proposed.

Influence of residual charge on repetitively nanosecond pulsed dielectric barrier discharges in atmospheric air

The plane-to-plane dielectric barrier discharge within 5 mm air gap driven by repetitive nanosecond pulses is studied. A water resistance (WR) is connected in parallel with the discharge circuit. For the discharge without the WR, two reverse discharges occur in the falling front of the voltage pulse, and besides, the primary discharge occurs in the rising front. For the discharge with the WR, only the primary discharge takes place, and the voltage waveform is changed into the unipolar positive voltage pulse with the elevated fall time. Additionally, the discharge with the WR displays the intermediate between the traditional diffuse and filamentary modes. Moreover, the uniformity of the discharge with the WR is increased as the pulse repetition frequency decreases from 1200 Hz to 100 Hz. The above observations in the discharge with the WR are mainly attributed to the increase in the residual charge at the inception of the following pulsed discharge.

Multiple Physical Time Scales and Dead Time Rule in Few-Nanometers Sized Graphene-SiOx-Graphene Memristors.

The resistive switching behavior in SiOx-based phase change memory devices confined by few nanometer wide graphene nanogaps is investigated. Our experiments and analysis reveal that the switching dynamics is not only determined by the commonly observed bias voltage dependent set and reset times. We demonstrate that an internal time scale, the dead time, plays a fundamental role in the system's response to various driving signals. We associate the switching behavior with the formation of microscopically distinct SiOx amorphous and crystalline phases between the graphene electrodes. The reset transition is attributed to an amorphization process due to a voltage driven self-heating; it can be triggered at any time by appropriate voltage levels. In contrast, the formation of the crystalline ON state is conditional and only occurs after the completion of a thermally assisted structural rearrangement of the as-quenched OFF state which takes place within the dead time after a reset operation. Our results demonstrate the technological relevance of the dead time rule which enables a zero bias access of both the low and high resistance states of a phase change memory device by unipolar voltage pulses.

A Novel CH5 Inverter for Single-Phase Transformerless Photovoltaic System Applications

Versatile single-phase voltage source inverters with unipolar voltage pulse and leakage current elimination capability have been extensively investigated for transformerless PV systems in the literature. However, the innovative current source inverters with leakage current elimination capability are not well explored. In this brief, a novel single-phase current source H5 (CH5) inverter is proposed. Only one extra IGBT is needed, but the leakage current can be significantly suppressed with a novel space vector modulation. Finally, the experimental tests are carried out on a single-phase CH5 inverter and the experimental results verify the effectiveness of the proposed topology and space vector modulation.

Micromagnetic simulation of electric-field-assisted magnetization switching in perpendicular magnetic tunnel junction

The feasibility of a voltage assisted unipolar switching in perpendicular magnetic tunnel junction (MTJ) has been studied using a micromagnetic simulation. Assuming a linear modulation of anisotropy field with voltage, both parallel (P) to anti-parallel (AP) and AP to P switchings were observed by application of unipolar voltage pulse without external magnetic field assistance. In latter case, the final P state can only be achieved with an ultrashort voltage pulse which vanishes before spin transfer torque (STT) becomes dominant to restore the initial AP state. In addition, it was found that the larger change in anisotropy field is required for the MTJ with smaller diameter.

Ozone generation in a kHz-pulsed He-O2 capillary dielectric barrier discharge operated in ambient air

The generation of reactive oxygen species using nonequilibrium atmospheric pressure plasma jet devices has been a subject of recent interest due to their ability to generate localized concentrations from a compact source. To date, such studies with plasma jet devices have primarily utilized radio-frequency excitation. In this work, we characterize ozone generation in a kHz-pulsed capillary dielectric barrier discharge configuration comprised of an active discharge plasma jet operating in ambient air that is externally grounded. The plasma jet flow gas was composed of helium with an admixture of up to 5% oxygen. A unipolar voltage pulse train with a 20 ns pulse risetime was used to drive the discharge at repetition rates between 2–25 kHz. Using UVLED absorption spectroscopy centered at 255 nm near the Hartley-band absorption peak, ozone was detected over 1 cm from the capillary axis. We observed roughly linear scaling of ozone production with increasing pulse repetition rate up to a “turnover frequency,” beyond which ozone production steadily dropped and discharge current and 777 nm O(5P→5S°) emission sharply increased. The turnover in ozone production occurred at higher pulse frequencies with increasing flow rate and decreasing applied voltage with a common energy density of 55 mJ/cm3 supplied to the discharge. The limiting energy density and peak ozone production both increased with increasing O2 admixture. The power dissipated in the discharge was obtained from circuit current and voltage measurements using a modified parallel plate dielectric barrier discharge circuit model and the volume-averaged ozone concentration was derived from a 2D ozone absorption measurement. From these measurements, the volume-averaged efficiency of ozone production was calculated to be 23 g/kWh at conditions for peak ozone production of 41 mg/h at 11 kV applied voltage, 3% O2, 2 l/min flow rate, and 13 kHz pulse repetition rate, with 1.79 W dissipated in the discharge.

Hardness of Nanocrystalline TiO<sub>2</sub> Thin Films

In this work results of hardness investigations of nanocrystalline TiO2 thin films are presented. Thin films were prepared by low pressure hot target reactive sputtering (LPHTRS) and high energy reactive magnetron sputtering (HERMS). In both processes a metallic Ti target was sputtered under low pressure of oxygen working gas. After deposition by LPHTRS TiO2 thin films with anatase structure were obtained and after additional post-process annealing at 1070 K, these films recrystallized into the rutile structure. Annealing also resulted in an increase of average crystallite size from 33 nm (for anatase) to 74 nm (for rutile). The HERMS process is a modification of the LPHTRS process with the addition of an increased amplitude of unipolar voltage pulses, powering the magnetron. This effectively increases the total energy of the depositing particles at the substrate and allows dense, nanocrystalline (8.7 nm crystallites in size) TiO2 thin film with the rutile structure to be formed directly. The hardness of the films was determined by nanoindentation. The results showed that the nanocrystalline TiO2-rutile thin film as-deposited using HERMS had high hardness (14.3 GPa), while the TiO2-anatase films as-deposited by LPHTRS, were 4-times lower (3.5 GPa). For LPHTRS films recrystallized by additional annealing, the change in thin film structure from anatase to rutile resulted in an increase of film hardness from 3.5 GPa to only 7.9 GPa. The HERMS process can therefore produce the TiO2 rutile structure directly, with hardness that is 2 times greater than rutile films produced by LPHTRS with additional annealing step.

Photon-Drag Effect in Single-Walled Carbon Nanotube Films

We observed an interaction of single-walled carbon nanotube films with obliquely incident nanosecond laser radiation in visible and infrared regions generating unipolar voltage pulses replicating the shape of the laser pulses. The photoelectric signal significantly depends on the laser polarization and has maximum value at the laser beam incidence angle of ±65° and at the film thickness of 350 nm. The results are explained in the framework of the photon-drag effect.

An experimental study on discharge mechanism of pulsed atmospheric pressure glow discharges

The discharge mechanism of pulsed atmospheric pressure glow discharges excited by the unipolar positive voltage pulses between two parallel plate electrodes with or without one dielectric barrier on the ground electrode in flowing helium has been characterized by nanosecond time resolved optical and electrical measurements. The uniform glow discharges can only be achieved when the voltage pulse duration is less than 1 μs with bare electrodes. With introducing a dielectric barrier on the ground electrode, a model of electrons traveling on the background ions between two discharge events is proposed to explain the discharge mechanism and characteristics in terms of discharge ignition, discharge spatial profile and discharge current amplitude.

Excitation of atmospheric pressure uniform dielectric barrier discharge using repetitive unipolar nanosecond-pulse generator

Dielectric barrier discharge (DBD) excitation by unipolar high voltage pulses is a promising approach for producing non-thermal plasma at atmospheric pressure. In this study, a magnetic compression solid-state pulsed power generator was used to produce repetitive nanosecond pulses for the excitation. The DBD is created using two liquid electrodes. The electrical characteristics of the discharge voltage and current are illustrated under different experimental conditions. The nanosecond-pulse discharge current is of the order of tens of amperes. This differs from common DBD current excitated by high-voltage ac sources. Compared with the characteristics of two current pulses corresponding to two discharges for unipolar pulsed-excitation, the secondary discharge in this study is minor owing to the pulsed power and discharge configuration. Under the experimental conditions, the luminous emissions from the front and side views of the liquid electrodes show that no filament is observed and the discharge is homogeneous and diffuse in the whole discharge region. The effects of applied voltage amplitude, repetition rate, and air gap spacing on the discharge characteristic are investigated. The discharge mode does not change with the variation of the investigated parameters. A comparison of high voltage ac and nanosecond-pulse excitation is also presented. In addition, discussion of the experimental results is presented.