Bipolar Nanosecond Pulse Research Articles

Generation of Large-Scale Plasma Jet with Excitation of Bipolar Nanosecond Pulse Voltage in Single-Spiral Electrode Configuration

In this study, a single-outer-spiral electrode with inductance of 20 μH is employed to couple the energy input of a bipolar nanosecond pulse for the purpose of generating a large-scale atmospheric pressure plasma jet. When the spiral electrode is wrapped around a plasma jet tube with a length of 35 cm, the electrical field can be optimized, resulting in a stable laminar flow field, and a plasma jet with a length and diameter larger than 14 cm and 1.2 cm can be generated. A comparative study of the bipolar and unipolar pulse excitation voltages is also conducted, showing that the maximum lengths of the plasma jet excited by a bipolar pulse voltage, positive pulse voltage, and negative are 14 cm, 10 cm, and 7 cm, respectively. The temporal and spatially resolved spectra of the plasma jets excited by both bipolar and unipolar pulses are investigated, respectively, and the main physiochemical processes of the active species and the plasma dynamics’ evolution are discussed.

The interaction between filaments in dielectric barrier discharge excited by bipolar/unipolar nanosecond pulse powers

This study investigates the behavior of discharge filaments in dielectric barrier discharges with a focus on the effects of nanosecond pulse voltage polarity. We observed significant repulsion between discharge filaments when the pin electrode was grounded in bipolar nanosecond pulse discharge. The tilt angle of the filaments was directly proportional to the peak current, which is indicative of charge density. When the bare pin electrode acted as an H.V. electrode, the repulsion phenomenon was diminished. Surface charges released through the bare pin electrode instead of accumulated on the dielectric surface accounts for this phenomenon. The study also highlights the impact of bipolar versus unipolar nanosecond pulse powers. The addition of a water resistor (WR) results in a slower falling edge of the pulse voltage and the absence of subsequent reverse discharges. The repulsion between filaments disappears both in pin-to-ground discharge and pin-to-H.V. discharge. The introduction of WR leads to a reduction of the current pulse’s duration and a premature termination of the discharge process, resulting the influence of surface charges on filament positioning negligible. It is hypothesized that the spatial distribution of ions does not exhibit significant repulsion, attributed to their substantial mass and sparse distribution in space.

Bipolar nano-second pulse power supply for electrochemical micromachining of tungsten carbide without tool wear

Electrochemical machining (ECM) of tungsten carbide (WC) alloy using bipolar pulses with a neutral electrolyte (NaNO3 aq) was successfully proposed in recent years. However, tool electrode wear always occurs during machining in the period of negative pulses. To solve this problem, a method of ECM with sacrificial auxiliary electrode using bipolar current is presented. This paper is focusing on the development of nano-second pulse bipolar power supply for this method. Firstly, positive and negative nanosecond pulses are obtained with the method of DC voltage chopping by using a multi-channel high-speed switch composed of gallium nitride (GaN) transistors. Then, these pulses are accordingly distributed onto the electrodes between tool electrode, workpiece electrode and auxiliary electrode during ECM in different time. During the period of positive pulses, the workpiece anode and tool cathode form a circuit for ECM, which dissolve the workpiece and form a passive film (tungsten oxide) on tungsten carbide; during the period of negative pulses, the workpiece cathode forms a loop with the auxiliary anode, resulting in hydrogen evolution reaction on the surface of workpiece, so as to weaken the adhesion of the passive film and improve the pH value of the electrolyte close to the machining area on workpiece surface to dissolve the tungsten oxide. ECM experiments were carried out with the developed power supply, and the micro holes are successfully machined on the surface of tungsten carbide without tool wear, which verifies the feasibility of the presented method and designed bipolar pulse power supply.

Multiphysics modelling of electroporation under uni- or bipolar nanosecond pulse sequences

A nonlinear dispersive multiphysics model of single-cell electroporation was proposed in this paper. The time-domain Debye model was utilised to describe the membrane dispersion while the dynamic pore radius function was deployed to modify the plasma membrane conductivity. The dynamic spatial distributions of the ion concentration were dominated by the Nernst-Planck function. First, a single nanosecond pulsed electric field was applied to verify our model and to explore the effects of dispersion and dynamic pore radius on the redistribution of the electric field. The dispersive membrane was found to increase the transmembrane potential, expedite the electroporation process, and weaken the membrane permeability; however, adding the dynamic pore radius function had the opposite effect on transmembrane potential and membrane permeability. The responses of the cells exposed to unipolar and bipolar nanosecond pulse sequences were subsequently simulated. During the application of unipolar pulse sequences, the pore radius and perforation area showed a step-like accumulation, and significant increases in the perforation area and intracellular ion concentration were observed with higher frequency pulse sequences and wider subpulse intervals. The bipolar cancellation effect was also observed in terms of membrane permeability and pore radius.

Silicon nanowires: the promoter of performance improvement of microplasma in a microcavity array device

A microcavity array device decorated by silicon nanowires (SiNWs) is fabricated and the discharge property improvement is investigated. The array device can be operated stably from several kPa to atmospheric pressure of argon, powered by a 20 kHz bipolar nanosecond pulse source. Profiting by electron emission from SiNWs, the microplasma discharge dynamics and emission properties are significantly enhanced. Experimental results manifest that the instantaneous total current of the device decorated by SiNWs is up to ∼20% higher than that of the device without SiNWs and the mean current is increased by ∼12.5% compared with the conventional device (without SiNWs), and the ignition voltage decreased by ∼24%. The setup time is less than 90 ns before the device is fully ignited, and emission intensity enhanced by over 60% compared with the conventional plain surface device. Moreover, calculated by Lissajous figures, the discharge power of proposed device is higher than that of the traditional device with increment of ∼26%, and the impact of SiNWs on microdischarge processes is analyzed. The mechanism of the microplasma property enhancement is discussed through introducing the electric field enhancement effect at SiNWs cap and initial seed electrons emitted from SiNWs. This work combines the characteristic advantages of SiNWs with microcavity gas discharge to achieve the performance improvement of microplasma, and the results reported here has profound impacts on improving microplasma discharge properties and implies potential significance in promoting the performance of plasma applications.

Ionization wave propagation characteristics under different polarity of pulse waveforms in micro-DBD device driven by bipolar nanosecond pulse waveform

Different spatiotemporal modes of ionization wave propagation at opposite polarity of bipolar pulses in a micro-dielectric barrier discharge structure device are investigated. The device is fabricated on a heavily doped n-type silicon substrate, and a 1 cm × 1 cm square cavity is formed on the 180 μm-thick polyimide film. Different modes of ionization wave propagation determined by the polarity of bipolar pulses are observed, and the details of streamerlike mode and wavelike mode under positive and negative half cycles of pulses are investigated, respectively. The propagation speeds of streamerlike ionization waves and wavelike ionization waves are ∼120 km/s and ∼40 km/s on average and ∼150 km/s and ∼70 km/s in maximum, respectively. Different parameters of bipolar pulses, especially the rising time of pulses, are applied to the proposed device to explore the variation of ionization wave propagation properties. The results show that the modes of the ionization wave propagation are barely changed when the device is driven by different rising time pulses. However, the initial plasma generation time and propagation speed are greatly changed. With a decrease in the rising time from 400 ns to 50 ns, the initial plasma generation time is brought forward over 200 ns, and the ionization wave propagation speed is improved over 30% for both cases. The results imply great significance in the exploration of the dynamics of plasma discharge evolution and regulation of plasma discharge properties through manipulating the pulse parameters.

Enhanced Breakdown Strength and Thermal Conductivity of BN/EP Nanocomposites with Bipolar Nanosecond Pulse DBD Plasma Modified BNNSs.

Filling epoxy resin (EP) with boron nitride (BN) nanosheets (BNNSs) can effectively improve the thermal conductivity of BN/EP nanocomposites. However, due to the few hydroxyl groups on the surface of BNNSs, silane coupling agent (SCA) cannot effectively modify BNNSs. The agglomeration of BNNSs is severe, which significantly reduces the AC breakdown strength of the composites. Therefore, this paper uses atmospheric pressure bipolar nanosecond pulse dielectric barrier discharge (DBD) Ar+H2O low temperature plasma to hydroxylate BNNSs to improve the AC breakdown strength and thermal conductivity of the composites. X-ray photoelectron spectroscopy (XPS) shows that the hydroxyl content of the BNNSs surface increases nearly two fold after plasma modification. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) show that plasma modification enhances the dehydration condensation reaction of BNNSs with SCA, and the coating amount of SCA on the BNNSs surface increases by 45%. The breakdown test shows that the AC breakdown strength of the composites after plasma modification is improved under different filling contents. With the filling content of BNNSs increasing from 10% to 20%, the composites can maintain a certain insulation strength. Meanwhile, the thermal conductivity of the composites increases by 67% as the filling content increases from 10% (SCA treated) to 20% (plasma and SCA treated). Therefore, the plasma hydroxylation modification method used in this paper can provide a basis for the preparation of high thermal conductivity insulating materials.

Nanosecond Pulsed Array Wire-to-Wire Surface Dielectric Barrier Discharge in Atmospheric Air: Electrical and Optical Emission Spectra Characters Influenced by Quantity of Electrodes

In this paper, an array wire-to-wire surface dielectric barrier discharge (DBD) structure is used to generate large-scale plasma by bipolar nanosecond pulse power in atmospheric air. The quantity of electrodes can be adjusted from 1 to 10 for varying discharge area. The applied voltage and discharge current are measured, the discharge images are captured, and optical emission spectra (OES) are collected. The discharge power, discharge area, and OES intensity for a single group of/and whole structure are calculated. The vibrational and rotational temperatures are simulated by the OES of N2 (C-B, $\Delta \nu =-2$ ), and the effects of the quantity of electrodes on discharge current, discharge power, discharge area, OES intensity, and vibrational and rotational temperatures are investigated. The results show that the discharge current has two main peaks during single applied pulse voltage, and decays in a fluctuant type. As the quantity of electrodes increases, the peak value of discharge current increases and the decaying time from peak value to zero around becomes longer. The discharge power, discharge area, and OES intensity have increasing tendencies, and those of the single group of wires decrease. In addition, when the quantity of electrodes increases, the vibrational temperature increases first and then decreases, and the rotational temperature varies in a fluctuant type.

Volume added surface barrier discharge plasma excited by bipolar nanosecond pulse power in atmospheric air: optical emission spectra influenced by gap distance

In this paper, volume barrier discharge with different gap distances is added on the discharge border of high-voltage electrode of annular surface barrier discharge for generating volume added surface barrier discharge (V-SBD) excited by bipolar nanosecond high-voltage pulse power in atmospheric air. The excited V-SBDs consist of surface barrier discharge (d = 0 mm) and volume added surface barrier discharges (d = 2 mm and 3 mm). The optical emission spectra are recorded for calculating emission intensities of N2 (C3Πu → B3Πg) and (B2 → X2 ), and simulating rotational and vibrational temperatures. The influences of gap distance of V-SBD on emission intensity and plasma temperature are also investigated and analyzed. The results show that d = 0 mm structure can excite the largest emission intensity of N2 (C3Πu → B3Πg), while the existence of volume barrier discharge can delay the occurrence of the peak value of the emission intensity ratio of (B2 → X2 )/N2 (C3Πu → B3Πg) during the rising period of the applied voltage pulse and weaken it during the end period. The increasing factor of emission intensity is effected by the pulse repetition rate. The d = 3 mm structure has the highest threshold voltage while it can maintain more emission intensity of N2 (C3Πu → B3Πg) than that of d = 2 mm structure. The structure of d = 2 mm can maintain more increasing factor than that of the d = 3 mm structure with varying pulse repetition rate. Besides, the rotational temperatures of three V-SBD structures are slightly affected when the gap distance and pulse repetition rate vary. The vibrational temperatures have decaying tendencies of all three structures with the increasing pulse repetition rate.

A high-repetition-rate bipolar nanosecond pulse generator for dielectric barrier discharge based on a magnetic pulse compression system

Magnetic pulse compression (MPC) systems are suitable for generating dielectric barrier discharges (DBDs) owing to their capability of producing high-amplitude, short pulse voltage waves. This paper proposes a high-frequency, bipolar magnetic compression system to study DBD plasma characteristics. First, the principle of bipolar MPC is explained [a bipolar MPC system comprises a full bridge inverter circuit, pulse transformer (PT), and magnetic switch (MS)]. Additionally, the design of the PT and MS is described. Then, the waveform of the resistive load is tested and compared with PSpice simulation results. It was found that the nanosecond pulse generator produces a pulse on a resistor with an amplitude of 0-13 kV, a rise time of approximately 100 ns, and a repetition frequency of 0 to several kHz. Finally, this paper studies the plasma characteristics under the application of a high-frequency bipolar pulse, and the charge-voltage Lissajous figure of the discharge waveform is analyzed. Combining discharge photographs and theoretical calculation results yields the relationship between the discharge characteristics and the frequency, which enriches the theoretical study of high-frequency bipolar discharges.

Spectroscopic and electrical characters of SBD plasma excited by bipolar nanosecond pulse in atmospheric air

In this paper, an atmospheric surface barrier discharge (SBD) generated by annular electrodes in quartz tube is presented through employing bipolar nanosecond pulse voltage in air. The discharge images, waveforms of pulse voltage and discharge current, and optical emission spectra emitted from the discharges are recorded and calculated. A spectra simulation method is developed to separate the overlap of the secondary diffraction spectra which are produced by grating in monochromator, and N2 (B3Πg→A3Σu+) and O (3p5P→3s5S2o) are extracted. The effects of pulse voltage and discharge power on the emission intensities of OH (A2Σ+→X2Пi), N2+ (B2Σu+→X2Σg+), N2 (C3Πu→B3Πg), N2 (B3Πg→A3Σu+), and O (3p5P→3s5S2o) are investigated. It is found that increasing the pulse peak voltage can lead to an easier formation of N2+ (B2Σu+) than that of N2 (C3Πu). Additionally, vibrational and rotational temperatures of the plasma are determined by comparing the experimental and simulated spectra of N2+ (B2Σu+→X2Σg+), and the results show that the vibrational and rotational temperatures are 3250±20K and 350±5K under the pulse peak voltage of 28kV, respectively.

Experimental study on surface modification of PET films under bipolar nanosecond-pulse dielectric barrier discharge in atmospheric air

Abstract Dielectric barrier discharge (DBD) is widely used for surface modification of polymer films. In this paper, DBD characteristics under bipolar repetitive frequency nanosecond pulse in atmospheric air are studied and surface properties of polyethylene terephthalate films under homogeneous DBD and filamentary DBD modification are compared through scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and dielectric test equipment. It is found that the discharge is homogeneous when gap spacing d is less than 1.2 mm and filamentary when d is within the range of 3.0 mm to 5.8 mm. SEM pictures reveal that films under homogeneous DBD present a smooth surface while intensive “gully-like” etches appear on the surface of the films under filamentary DBD, which can result in local insulation defects and is disadvantageous to surface modification. It is found from the XPS analysis that a number of oxygen-containing polar groups are introduced onto the surface of the film modified by homogeneous DBD compared with the untreated one. Experimental results for dielectric properties indicate that the three parameters: relative dielectric constant ɛr, dielectric loss tangent tan δ and breakdown voltages Vb are all changed in different degree after surface modification. And possible reason for the phenomenon is discussed.

Electrical and optical characteristics of diffuse nanosecond pulsed discharge plasma using a needle-array electrode in atmospheric air

In this paper, a stable and diffuse dielectric barrier discharge plasma excited by bipolar nanosecond pulse is obtained under a needle-array electrode at atmospheric pressure in air. The images of the diffuse discharge, electric characteristics, and the optical emission spectra emitted from the diffuse discharge are investigated under mono and multi needle electrodes configuration. The peak value of discharge current, the average power, the power density, the emission intensity of N2 (C3Πu →B3Πg, 0-0), and the gas temperature of the diffuse dielectric barrier discharge plasmas are investigated under different needle electrode numbers based on the waveforms of pulse voltage-current and the optical emission spectra. Moreover, the plasma area is obviously enlarged in the transverse direction when the needle electrode number is increased from 1 to 13. An area approximately 65 × 45 mm2 diffuse discharge plasma region under 13 needle electrodes can be obtained and the discharge plasma still keeps good uniformity, which could be used for large-area surface processing in several fields spanning from biological sterilization and plasma medicine to surface modification of materials and synthesis of functional materials.

Optical and application study of gas–liquid discharge excited by bipolar nanosecond pulse in atmospheric air

In this study, a bipolar nanosecond pulse with 20ns rising time is employed to generate air gas–liquid diffuse discharge plasma with room gas temperature in quartz tube at atmospheric pressure. The image of the discharge and optical emission spectra of active species in the plasma are recorded. The plasma gas temperature is determined to be approximately 390K by compared the experimental spectra with the simulated spectra, which is slightly higher than the room temperature. The result indicated that the gas temperature rises gradually with pulse peak voltage increasing, while decreases slightly with the electrode gap distance increasing. As an important application, bipolar nanosecond pulse discharge is used to sterilize the common microorganisms (Actinomycetes, Candida albicans and Escherichia coli) existing in drinking water, which performs high sterilization efficiency.

An atmospheric air gas-liquid diffuse discharge excited by bipolar nanosecond pulse in quartz container used for water sterilization

In this Letter, we report that the air gas-liquid diffuse discharge plasma excited by bipolar nanosecond pulse in quartz container with different bottom structures at atmospheric pressure. Optical diagnostic measurements show that bountiful chemically and biologically active species, which are beneficial for effective sterilization in some areas, are produced. Such diffuse plasmas are then used to treat drinking water containing the common microorganisms (Candida albicans and Escherichia coli). It is found that these plasmas can sterilize the microorganisms efficiently.

A large-area diffuse air discharge plasma excited by nanosecond pulse under a double hexagon needle-array electrode

A large-area diffuse air discharge plasma excited by bipolar nanosecond pulse is generated under a double hexagon needle-array electrode at atmospheric pressure. The images of the diffuse discharge, electric characteristics, and the optical emission spectra emitted from the diffuse air discharge plasma are obtained. Based on the waveforms of pulse voltage and current, the power consumption, and the power density of the diffuse air discharge plasma are investigated under different pulse peak voltages. The electron density and the electron temperature of the diffuse plasma are estimated to be approximately 1.42×1011cm−3 and 4.4eV, respectively. The optical emission spectra are arranged to determine the rotational and vibrational temperatures by comparing experimental with simulated spectra. Meanwhile, the rotational and vibrational temperatures of the diffuse discharge plasma are also discussed under different pulse peak voltages and pulse repetition rates, respectively. In addition, the diffuse air discharge plasma can form an area of about 70×50mm2 on the surface of dielectric layer and can be scaled up to the required size.

An uniform DBD plasma excited by bipolar nanosecond pulse using wire-cylinder electrode configuration in atmospheric air

In this study, a bipolar nanosecond pulsed power supply with 15ns rising time is employed to generate an uniform dielectric barrier discharge using the wire-cylinder electrode configuration in atmospheric air. The images, waveforms of pulse voltage and discharge current, and the optical emission spectra of the discharges are recorded. The rotational and vibrational temperatures of plasma are determined by comparing the simulated spectra with the experimental spectra. The effects of pulse peak voltage, pulse repetition rate and quartz tube diameter on the emission intensities of N2 (C3Πu→B3Πg, 0–0) and N2+B2Σu+→X2Σg+,0–0 and the rotational and vibrational temperatures have been investigated. It is found that the uniform plasma with low gas temperature can be obtained, and the emission intensities of N2 (C3Πu→B3Πg, 0–0) and N2+B2Σu+→X2Σg+,0–0 rise with increasing the pulse peak voltage and pulse repetition rate, while decrease as the increase of quartz tube diameter. In addition, under the condition of 28kV pulse peak voltage, 150Hz pulse repetition rate and 7mm quartz tube diameter, the plasma gas temperature is determined to be 330K. The results also indicate that the plasma gas temperature keep almost constant when increasing the pulse peak voltage and pulse repetition rate but increase with the increase of the quartz tube diameter.

The effect of dielectric thickness on diffuse nanosecond dielectric barrier discharges using a needle array-plate electrode configuration in air at atmospheric pressure

A stable diffuse large-area air plasma with low gas temperature is developed under different dielectric thicknesses by using a needle array-plate electrode configuration in air at atmospheric pressure, which is excited by a bipolar nanosecond pulse power with about 20 ns rising time. The images of the diffuse discharge, electric characteristics, and the optical emission spectra emitted from the diffuse discharge are obtained under different dielectric thicknesses. The discharge area, the average power, the power density, and the emission intensities of N2 (C3Πu → B3Πg, 0-0) and N2+ (B2Σu+ → X2Σg+, 0-0) of the nanosecond dielectric barrier discharges are investigated under different dielectric thicknesses based on the waveforms of discharge voltage and discharge current and the optical emission spectra. The gas temperature of plasma is determined to be approximately 385±5 K by measuring the optical emission spectra of the N2+ (B2Σu+ → X2Σg+, 0-0), and decreases gradually with increasing dielectric thickness. Consistently, an area of approximately 2000 mm2 plasma region under 7 needle electrodes can be formed at 1 mm thick dielectric layer.

Atmospheric air homogenous DBD plasma excited by bipolar nanosecond pulse used for improving the hydrophilic property of polypropylene

In this paper, an air homogenous dielectric barrier discharge excited by bipolar nanosecond pulse voltage is obtained and used for the surface modification of polypropylene non-woven fabric at atmospheric pressure. Compared with the DBD plasma excited by sine alternating current (AC) voltage, nanosecond pulsed dielectric barrier discharge exhibits obvious advantages, e.g., better discharge homogeneity, lower energy cost, and lower plasma gas temperature etc. Hence it presents the potential application in improving the hydrophilic property of polypropylene non-woven fabric with high energy efficiency and without surface damage. To reduce the water contact angle of the polypropylene surface from 145° to 110°, the average energy cost of the nanosecond pulsed dielectric barrier discharge is only about 0.1 J/cm2, which is about 1/20 of AC dielectric barrier discharge. On the other hand, the surface damage of non-woven fabric induced by nanosecond pulsed dielectric barrier discharge plasma cannot be distinguished by SEM photographs.

Effect of dielectric material on bipolar nanosecond pulse diffuse dielectric barrier discharge in air at atmospheric pressure

In this paper, dielectric plates made by ceramic, quartz and polytetrafluoroethylene (PTFE) respectively are employed to generate low gas temperature, diffuse dielectric barrier discharge plasma by using a needle-plate electrode configuration in air at atmospheric pressure. Both discharge images and the optical emission spectra are obtained while ceramic, quartz and PTFE are used as dielectric material. Plasma gas temperature is also calculated by comparing the experimental emission spectra with the best fitted spectra of N2 (C3Πu→B3Πg 1–3) and N2 (C3Πu→B3Πg 0–2). The effects of different pulse peak voltages and gas gap distances on the emission intensity of N2 (C3Πu→B3Πg, 0–0, 337.1nm) and the plasma area on dielectric surface are investigated while ceramic, quartz and PTFE are used as dielectric material. It is found that the permittivity of dielectric material plays an important role in the discharge homogeneity, plasma gas temperature, emission spectra intensity of the discharge, etc. Dielectric with higher permittivity i.e., ceramic means brighter discharge luminosity and stronger emission spectra intensity of N2 (C3Πu→B3Πg, 0–0, 337.1nm) among the three dielectric materials. However, more homogeneous, larger plasma area on dielectric surface and lower plasma gas temperature can be obtained under dielectric with lower permittivity i.e., PTFE. The emission spectra intensity and plasma gas temperature of the discharge while the dielectric plate is made by quartz are smaller than that while ceramic is used as dielectric material and bigger than that when PTFE is used as dielectric material.