Unipolar Pulse Research Articles

Особенности импульсного инициирования плазменной струи

The generation of a cold plasma jet of atmospheric pressure in helium by unipolar positive pulses excitation at a voltage of 2–6 kV and the impact on a dielectric target made of aluminum oxide has been studied. It is shown that the main parameter influencing the regular nature of the streamer breakdown is the pulse duration, and the achievable parameters of cold plasma impact on the target identical to those for sinusoidal excitation.

Поправка к статье Усиление электрической площади импульса при отражениях от движущегося зеркала" Оптика и спектроскопия 130 (9), 1402--1404 (2022)

It is indicated that sets of plane-parallel layers of linear materials do not reflect the zero-frequency component of the incident pulse and therefore cannot serve as mirrors for unipolar pulses. The amplification of the electric area is possible with Fresnel reflection from an unlimited medium with a refractive index lower than that of the medium in which the incident pulse propagates. The same is realized in the case of a thick layer of such a medium with the exclusion of the influence of reflection by its rear face due to the slope or roughness of the face. The movement of the boundary does not lead to an additional amplification of the electric area, since the increase in the peak amplitude of the wave upon reflection is compensated by a decrease in the pulse duration.

Investigation of Partial Discharges in AlN Substrates under Fast Transient Voltages

The objective of this article is to characterize partial discharge (PD) inception voltages and patterns at sinusoidal and square voltages in insulating ceramic substrates with generic manufacturing defects. PD tests were conducted on active metal brazed (AMB) aluminum nitride (AlN) substrates either with cavities in the polymer coating or sharp protrusions of the metal brazing. The substrates were tested in silicone liquid instead of silicone gel. Light sensitive imaging was used to localize the PD sites on the surface. PDs at square voltage with rise time of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6 ~\mu \text{s}$ </tex-math></inline-formula> were measured with a high-frequency current transformer and a photomultiplier. In both substrate types, the peak–peak value of the PD inception voltage (PDIV) was higher at sinusoidal voltage compared to peak-peak value of the square wave. This difference was more pronounced in uncoated substrates, where discharges incepted at sharp edges surrounded by silicone liquid. For both types of defects, comparable PDIVs were measured at bipolar and unipolar square waves. Results for unipolar pulses are discussed considering the role of charge memory effect.

Time and space waveform optimization to extend the harmonic cutoff and to produce the water window single attosecond pulse

Abstract Based on the three-step theory of high-order harmonic generation, the harmonic cutoff is very sensitive to the few-cycle laser waveform in both time and space regions. Therefore, in this paper, we propose the method to control the harmonic cutoff and to produce the water window attosecond pulse through the optimization of time and space waveform. It is found that, in the time region, by properly choosing the delay and phase of the few-cycle two-color pulse, not only the harmonic intensity is enhanced, but also the quantum path of the harmonic emission can be controlled. Further, with the introduction of the 3rd pulse (i.e., the infrared pulse or the unipolar pulse), the harmonic cutoff from the single harmonic emission peak can be extended, showing a water window harmonic plateau. In the space region, by using the positive spatial inhomogeneous effect, the harmonic cutoff from the basic two-color waveform can also be extended, which leads to a water window spectral continuum. Finally, by Fourier transformation of harmonics during the water window region, the ultrashort single 29 as pulses can be obtained.

Using N-Norms for Analyzing Symmetric Protective Electrical Circuits with Triple Modal Reservation

The redundancy of functional blocks and critical assemblies in radio-electronic equipment is among the most widely used techniques for increasing reliability. Complex redundant systems raise the problem of electromagnetic compatibility (EMC). Ignoring EMC requirements can lead to partial or complete REE failures. In this paper, the authors analyze a noise-protective electrical circuit with triple modal reservation (a promising type of cold redundancy). A multilayer stripline is investigated, the conductors of which are symmetrically arranged relative to two planes. On account of the strong electromagnetic coupling, this protective circuit can decompose dangerous ultra-wideband (UWB) interference received at the input of the primary or redundant circuits into unipolar pulses of lower amplitude. Using this approach, due to the symmetry of the conductors, equal decomposition efficiency could be achieved. However, the effect of UWB interference at the input of one of the conductors produces bipolar pulses at the output of the other conductors. In this paper, the authors evaluate the dangers of unipolar and bipolar decomposed pulses and use modal analysis to mathematically determine the polarities and amplitudes of the decomposed pulses at all output nodes for a pseudo-matched structure. By using the quasistatic approach with and without losses, the time responses to a trapezoidal pulse with a total duration of 60 ps, which simulates UWB interference, are obtained. To confirm the results of modal analysis and quasistatic simulation, an experimental study is performed. Using a stroboscopic oscilloscope DSA 8300, the authors obtained a transient response to a step excitation. Then, taking the derivative, the response to a trapezoidal pulse with a total duration of 140 ps was obtained. To analyze the criticality of the decomposed pulses, N-norms are used. In the general case, it is shown that the UWB interference is decomposed into four pulses of lower amplitude. At the same time, the value of each N-norm indicates its significant attenuation. For example, the amplitude of the UWB pulse acting on the input of the reserved conductor decreases by 10.31–8.93 times. Such results numerically demonstrate the high efficiency of the suggested approach when it comes to protecting equipment against UWB interference. It is also shown that the probability of dielectric breakdown and damage to electronic components in redundant circuits is lower than in a primary circuit. This is due to the fact that the value of N3 in the redundant circuit is 2.38 times less than in the primary circuit. However, the results demonstrate that arcing is highly probable both in primary and redundant circuits. Finally, aspects of symmetry/asymmetry in the problem under investigation are emphasized.

Design and implementation of a CSI inverter with unipolar SPWM modulation and PR controller for lineal loads

This paper presents a detailed implementation of a current source inverter using unipolar sinusoidal pulse width modulation. This method is uncommon in these types of inverters and the semiconductor devices, integrated circuits, sensors, and filters used in conjunction with the TMS320F28379D microcontroller will be discussed. The inverter was tested in both an open and closed loop with a proportional resonant controller. Satisfactory results in terms of the harmonic distortion factor at the voltage output and the regulation indices for lineal loads were obtained. The response circuit demonstrated its viability for the subsequent connection to an electrical distribution network.

Highly Efficient Transformerless Inverter with Flying-Capacitor Buck–Boost for Single-Phase Grid-Connected PV Systems

Grid-connected inverters (GCI) are commonly used in PV system applications to generate a regulated AC current to feed into the grid. Transformerless inverters are the most advanced inverters that are used in industry, which provide efficiency with smaller size and lower cost. This paper proposes a grid-connected single-phase transformerless inverter with the technology of common ground and the virtual DC bus concept. In this topology, the grid neutral is connected directly to the PV ground, which generates a constant common mode voltage (CMV), thus leading to the elimination of the leakage current caused by the PV array’s parasitic capacitance. The proposed inverter has a buck–boost circuit with a flying capacitor to generate the DC bus for a negative power cycle, four switches, and two diodes. A unipolar sinusoidal pulse width modulation (SPWM) technique is used which reduces the output filter requirements. In addition, only one switch carries the load current during the active states of both the negative and positive power cycle, thus minimizing the conduction losses. One more advantage presented in the proposed inverter is its ability to charge the flying capacitor during all operation states due to the existence of the buck–boost circuit. Design and theoretical calculations were conducted in this paper to optimize the losses. Moreover, the PSIM simulation was used to validate the proposed topology inverter, verify the performance by showing leakage current elimination, and achieve unipolar voltage in the output bus. The simulation results show a peak efficiency of 98.57% for a 2 kW inverter, which agrees with the theoretical calculations.

Effects of applied voltage waveform on the uniformity of a microplasma array confined inside polydimethylsiloxane microchannels

AbstractThe uniformity of the microplasma array is essential to modify the hydrophilicity of the inner surface of polydimethylsiloxane (PDMS) microchannels by plasma treatment. In this study, the effects of applied voltage waveforms on the uniformity of the microplasma array are investigated. Interestingly, the microplasma array excited by AC (alternate current) voltage looks more “uniform” by a digital camera and has higher gas temperature and electron density than that excited by unipolar and bipolar pulse voltage. Imaging the microplasma array by a fast intensified charge‐coupled device camera shows that the ignition of microplasma inside each microchannel has strong randomness in spatial distribution, and the opportunity of each microchannel being ignited is almost equal. Detailed analysis reveals that the low density of surface charges and the small overvoltage in the case of AC voltage are expected to play crucial roles in the stochastic behavior of microplasma ignition inside PDMS microchannels. This study is useful for understanding the uniformity of the microplasma array for surface modification of PDMS microchannels.

Time integration and differentiation of unipolar pulses of unusual shape

Based on the previously developed theory of transformation (time integration and differentiation) of ultrashort pulses in thin metal films, we study the possibility of time differentiation and integration of unipolar pulses. Unipolar pulses of unusual shape–rectangular and triangular–are considered, and their mutual transformation upon propagation through thin films with certain parameters is demonstrated. The conservation of the electrical area in such problems is shown.

Review on Solid-State-Based Marx Generators

Marx generators are widely used to produce transient high-voltage pulses. The evolution of semiconductor devices and power electronics concepts promotes the development of solid-state Marx generators (SSMGs) and enables them with flexible pulse modulation ability. First, this article sorts out the evolution of SSMGs topologies chronologically. We can see that how the energy efficiency of SSMGs is considerably improved by replacing resistors with diodes and switches and how square-wave pulses are generated by SSMGs based on half-bridge structures. Unipolar and bipolar pulses can be easily produced with different SSMGs. Second, we discuss the influence of rated voltage and rated power of present semiconductor switches on the performances of SSMGs since switches are the key components in pulse generators. To reduce the size and weight of SSMGs, metal–oxide–semiconductor field-effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) with small packages are preferable. Third, synchronous isolated driving of switches as the crucial technique in SSMGs is introduced. Different methods of providing synchronous signals and isolated power to various stages in SSMGs are illustrated. Fourth, the performance including load capacity, droop compensation, waveform modulation, and self-triggering of SSMGs is discussed. In the end, the developing trend of SSMGs is given.

Obtaining Unipolar Pulses at Far Field Zone of the Source

Obtaining Unipolar Pulses at Far Field Zone of the Source

Spatial distribution and time evolution of metal-containing plasma of a low-current atmospheric pressure discharge with magnesium cathode

The spatial intensity distribution and temporal dynamics of the plasma generated by an atmospheric pressure discharge with magnesium cathode in an argon flow are investigated in a coaxial geometry discharge system. The repetition rate of unipolar pulses was 56 kHz and the pulse duration was 12 μs. The steady-state amplitude of the discharge current was 100 mA at a voltage of about 130 V. Under this operating mode, a local melting of the active cathode surface took place. The evaporated magnesium atoms were captured by the working gas flow and formed a green glow plume around the positive discharge column outside the anode nozzle. The image of the plasma formation was projected onto the entrance slit of the monochromator. The spatial distribution of the radiation intensity and evolution in time of its selected monochromatic components were measured. The radiation spectrum contained groups of ion and magnesium atom lines with wavelengths of 285.21 nm (singlet resonant Mg I); 383.08, 383.36, 383.9 nm (triplet Mg I); 517.3, 517.5, 518.1 nm (triplet Mg I). The results of this work are promising with regard to studying open-type spontaneous radiation sources, as well as the generation of combined gas-metal plasma flows at atmospheric pressure.

Free Space Strange and Unipolar EM Pulses: Yes or No?

E.G. Bessonov suggested the time integrated strength of an electric field ∫−∞∞E(r,t)dt=SE(r) as a parameter to classify electromagnetic (EM) waves. Since then, this parameter has been studied and used in many works on microwave and laser physics, especially when it comes to unipolar, bipolar and few cycle EM pulses. In this paper, it is shown that SE(r)=0 is an identity for a wide class of free space pulses of finite total energy. This property can be useful in various applications of few cycle radiation and as a benchmark in EM and QED computations.

Effective streamer discharge control by tailored nanosecond-pulsed high-voltage waveforms

In this paper we present our solid-state nanosecond pulse source (the solid-state impedance-matched Marx generator) which can generate arbitrary waveforms and which can be used for pulsed discharge generation. The purpose of the development of such a generator is twofold: by being able to change the waveform at will, we aim to control the discharge generated by such pulses very precisely which can be very useful for plasma applications, but also for more fundamental studies. In the presented study, we applied the arbitrary-waveform pulse source for streamer discharge generation in a cylinder-wire-like arrangement and used the arbitrary-waveform capability to change the rise time (in our experiments we used 6.8–26.2 ns) of unipolar positive pulses with 6-10 kV amplitude and 80 ns duration. Additionally, we introduced variations of a step in the rising edge of the waveform. We performed measurements both in air and nitrogen to electrically characterize the discharge while analyzing the streamer propagation in the plasma reactor with intensified charge-coupled device imaging and measured ozone generation (in air). The results show that we can indeed control the propagation of the streamer discharge with the stepped waveform, but that the rise-time variation has little effect on the streamer propagation in our system. However, the streamer velocity and structure differs significantly comparing discharges in nitrogen and air for the same applied voltage waveform. Additionally, for some of the stepped waveforms we found a slight increase of the ozone yield for air at low overall energy densities.

Software designed to digitize transitional characteristics when conducting bioimpedance studies on a biological object

The essence of the article is to develop a method for the formation of descriptors intended for neural networking classifiers of medical risks based on the analysis of transition processes in the biomaterial in the in vivo experiment.The essence of the proposed method is to form the test effects of the probing current on the anatomical areas with anomalous electrical conductivity and obtaining the amplitude-phase-frequency characteristics of the impedance of the biomaterial to which the test effect was carried out. The coordinates of the Cowla’s graphic were used as descriptors. Cowla’s graphic was obtained on the basis of the conversion of Carson counts of the transition process in a quadrupole, the element of which is the impedance of the studied biomaterial. A sequence of unipolar rectangular pulses was supplied to the inlet of the quadrupole.It is shown that the linear model of the biomaterial impedance allows you to obtain descriptors based on its amplitude-phase-frequency characteristics, taking into account the dissipative properties of the biomaterial. The receipt of the Cowla’s graphic model with its dissipative properties, allows you to build medical risk classifiers for socially significant diseases.

Co-effect of dielectric layer material and driving pulse polarity on the spatial emission intensity distributions of micro dielectric barrier discharge

A micro concentric ring device with asymmetric dielectrics (glass and n-silicon) is driven by a bipolar pulse generator with 20 kHz frequency, 1 μs pulse width, 50 ns rising/falling time, and 3.6 kV peak-to-peak voltage, and the spatial emission intensity distributions in the device are investigated. The experiments are operated at 133 mbar pure argon. The spatial-temporal microplasma evolution recorded by intensified charge-coupled device illustrates that ‘edge emission’ arises in the microchannels when the electrode (indium tin oxide) on which the glass dielectric is located acts as the cathode. However, when the electrode (conductive silver paste) adjacent to the n-silicon acts as the cathode, ‘center emission’ is induced. The dielectric materials’ properties (relative permittivity and secondary electron emission coefficient), synergistically with the pulse polarity, which determines the influence of the residual long-living particles generated by previous discharge on the subsequent discharge, are inferred to be responsible for the distinct spatial emission intensity distributions at different pulse polarities. When the n-silicon is situated on the cathode, the high permittivity of n-silicon repels the electric field into plasma, which means that the electrons can obtain more energy in the first half of their journey. Furthermore, the high secondary electron yield of n-silicon makes it possible to provide more seed electrons for microdischarge. This mechanism of electrons dynamics leads to the occurrence of ‘center emission’. When the positive half period of the bipolar pulse arrives at the n-silicon, the residual charged particles generated by the previous discharge will induce a reversed electric field in the channel center to impair the applied electric field and bring about the ‘edge emission’, but this cannot emerge in the microdischarge powered by the unipolar pulse. Investigation of spatial emission intensity distributions of microplasmas is important for the comprehension of devices based on micro-structure techniques.

Incorporation of electroendocytosis and nanosecond pulsed electric field in electrochemotherapy of breast cancer cells

ABSTRACT The study aimed to evaluate the possibility to perform electrochemotherapy using nanosecond pulsed electric field (nsPEF) and low electric field (LEF) monopolar electrical impulses to alleviate the problems of conventional electroporation. Two types of pulses have been used to treat MCF-7 human breast carcinoma cell line: very low voltage (electric field strength) long trains of short unipolar electric pulses, and low frequencies of extremely intense (40kV/cm), ultra-short (10ns) electric pulses. The electropermeabilization efficiency of the formed endocytotic vesicles was measured using the cloning efficacy test. The cell viability was decreased significantly at a repetition frequency begins from 0.01 Hz by ~35% and reached complete cell loss at 1 Hz of nanosecond pulses for cells treated before with monopolar pulses at 20 V/cm in the presence of BLM with 4 µM concentration. The uptake of non-permeant drugs has been done without plasma membrane permeabilization (classical electroporation), but by endocytosis. Nanosecond electric pulses can disrupt the membrane of endocytotic vesicles and release the cytotoxic drug bleomycin.

Soliton-like unipolar objects in nonequilibrium dissipative media

For electromagnetic pulses without a carrier frequency, propagating in a system of multilevel atoms with a fast irreversible relaxation of the induced dipole moment, but a slow relaxation of the populations of quantum states, the nonlinear integro-differential equations of the ‘reaction–diffusion’ type are derived. One-dimensional soliton-like solutions of these equations in the form of unipolar pulses are found and analyzed. It is shown that such pulses can be formed in a nonequilibrium medium. These pulses transfer a medium to other metastable states, which depend on the input conditions. The propagation of these soliton-like signals is accompanied by a change in the populations of quantum states of atoms in the modes of switching waves with the memory of input conditions.

ПЕРЕТВОРЕННЯ ІМПУЛЬСНОЇ ЕНЕРГІЇ В МІКРОХВИЛІ В НЕЛІНІЙНИХ ЛІНІЯХ ПЕРЕДАЧІ

Purpose: Experimental results and numerical simulations are presented, concerning effects of microwave generation in coaxial transmission lines which are fed with unipolar, high voltage electric pulses. The work is aimed at clarifying the relative importance of several mechanisms that could be responsible for the appearance of microwave-frequency oscillations in the course of pulse propagation through the guiding structure. Design/methodology/approach: Dispersive and filtering properties of coaxial waveguides that involve three structural sections are discussed. These latter follow one another along the axis of symmetry. Two identical sections at the input and output are filled with an isotropic liquid dielectric, while the middle part may, in addition, be either partially or fully filled with a non-conductive gyrotropic material. The inserted core represents a set of ferrite rings showing a nonlinear response to the initial high voltage, pulsed excitation. Throughout the series of measurements, the diameters of the inner conductor and of the ferrite core were kept constant. The outer conductor’s diameter was varied to permit analysis of the effect of that size proper and of the degree to which the cross-section is fi lled with ferrite. The gyrotropic properties of the ferrimagnetic material were realized through application of a magnetic bias field from an external coil. The measurements were made for a variety of pulsed voltage magnitudes from the range of hundreds of kilovolts, and magnetic bias fields of tens kiloamperes per meter. Findings: As observed in our experiments, as well as in papers by other writers, a unipolar pulse coming from the radially uniform front-end section, further on gives rise to quasi-monochromatic voltage oscillations. These appear as soon as the pulse has advanced a sufficient distance into the radially nonuniform portion of the guide. The oscillations may consist of a small number of quasi-periods, which suggests a large spectral line width. However, by properly selecting geometric parameters of the wave guiding line and the characteristics of the initial pulsed waveform it proves possible to obtain output frequencies of about units of gigahertz and pulse powers at subgigawatt levels. Conclusions: The frequencies and amplitudes of the appearing oscillations, as well as their spectral widths, are governed by the complex of dispersive and non-linear properties of the guiding structure. The diameters of the inner and outer coaxial conductors in the line, diameter of the ferrimagnetic insert and its intrinsic linear dispersion determine the set of waveguide modes capable of propagating through the line. An oscillating part of the waveform may appear and get separated from the main body of the pulse if it has originated at a higher frequency than the cut-off value for a different mode than the initial TEM. Key words: unipolar pulse, coaxial transmission line, microwave frequency oscillations, dispersion laws, waveguide modes

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas–liquid discharge generated in atmospheric N2

In this paper, unipolar pulse (including positive pulse and negative pulse) and bipolar pulse voltage are employed to generate diffuse gas–liquid discharge in atmospheric N2 with a trumpet-shaped quartz tube. The current–voltage waveforms, optical emission spectra of excited state active species, FTIR spectra of exhaust gas components, plasma gas temperature, and aqueous H2O2, and production are compared in three pulse modes, meanwhile, the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied. The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge, differently, in bipolar pulse driven discharge, only one main discharge appears in a single voltage pulse time. The intensities of active species (OH(A), and O(3p)) in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min−1 of gas flow rate. The absorbance intensities of NO2 and N2O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate. Under the same discharge conditions, the bipolar pulse driven discharge shows lower breakdown voltage, and higher intensities of excited species (N2(C), OH(A), and O(3p)), nitrogen oxides (NO2, NO, and N2O), and higher production of aqueous H2O2, and compared with both unipolar positive and negative discharges.