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Surrounding air pollution is one of the important warnings to human health. It is necessary to detect hazardous pollutant gases in the air. The gas sensor is the candidate for such detection. Progress of smart and flexible sensors has been receiving growing curiosity in recent years because of their enormous sensing applications. Such smart and flexible sensors can be manufactured by depositing conducting materials, such as conducting polymer, carbon nanotube (CNT), graphene oxide, and metallic nanoparticles, onto nonconducting polymeric flexible substrates, such as paper, plastic films, and textiles. Most of the flexible polymeric substrates, such as polyethylene, polyester, nylon, and polypropylene, have low surface energy and poor wettability, which weakens the adhesion between conducting material and flexible substrate. Plasma surface modification is a novel technique to enhance surface properties to produce stable composites. This review focuses on various types of plasmas for surface modification and their effects on the surface after plasma treatment to improve the grafting and adhesion of the sensing layer with the substrate. The aim of this article is to systematically overview the development of plasma-enhanced smart and flexible gas sensors to date and to envisage their future progress. [ABSTRACT FROM AUTHOR]

The results presented in this article relate to the work conducted to verify the existence of anode-induced phenomena, predominantly anode vaporization and consequent prebreakdown (PBD) current enhancement due to the impact of positive ions and microparticles over a relatively larger area at the cathode (presumably ion-assisted field (I-F) emission like). The verification of this hypothesis is attempted using a three-electrode arrangement. One electrode is comprised of a needle insulated from and projecting through a plane electrode (collector) of 40-mm diameter. It was surmised that if the positive ion beam from the anode spot (due to electron beam impact) were to be macroscopically diffuse, at least the collector would gather a part of it. However, no currents could be detected in the collector circuit even at voltages close to breakdown. The needle currents continued to display the typical characteristics of PBD currents under alternating voltages. The needle currents depended on the spacing between the needle tip and the plane of the collector and the polytetrafluoroethylene (PTFE) insulation used to prevent emission from the immediate vicinity of the needle evaporated significantly. Typical broad-area electrode behavior displayed by needle currents indicated that I-F emission, if any, is limited to the needle itself, which is certainly broad compared to the positive ion beam. Dependence of the PBD currents and breakdown voltages on the melting point of the anode material lend support to such anode-triggered electrode phenomena. [ABSTRACT FROM AUTHOR]

Cancer is a devastating and life-threatening disease. It is the second leading cause of death worldwide after heart diseases. While science has significantly advanced to improve the treatment outcome and quality of life in cancer patients, there are still many issues with the current therapies, such as toxicity and the development of resistance to treatment. Among the novel tools to overcome these limitations is nonthermal plasma (NTP) and its treatment regimens. Recent progress in NTP devices with ion temperatures close to room temperature demonstrated significant potential in cancer therapy. NTP devices provide a unique combination of reactive oxygen species (ROS), reactive nitrogen species (RNS), photons, and electric fields that exhibit desirable properties of triggering cell death pathways, selectively for cancer cells. While in principle NTP is nonnecrotic and gentle to the tissue, but reactive oxygen and nitrogen species (RONS)-triggered tumor cell death exhibited to have pro-immunogenic properties. Many in vitro and in vivo experiments have demonstrated antitumor effects of direct NTP, synergistic applications of NTP with anticancer drugs/treatments, and plasma-conditioned medium (PCM) applications against a variety of cancer cells. The latest results and findings in this field are the subject of this review along with a brief lay-reader-explanation of cancer and immunology. In this review, initially, we give an overview of the literature that deals with studies on the use of NTP for cancer treatment. Subsequently, we present typical results from that literature to illustrate the advances of NTP in oncology. Finally, we discuss some challenges and future scopes offered by NTP for cancer treatment. [ABSTRACT FROM AUTHOR]

We describe the design, operation, and qualification of a coaxial plasma gun (CPG) in a low-pressure environment with a gas puff inlet. This infrastructure enables a CPG to operate in the deflagration mode followed by snowplow plasma sheath formation. These modes inject radially expanding and axially propagating plasma sheaths into a low-pressure residual background. This manuscript details the pulse power delivery circuit, including automatic logic control of subcircuits. High-speed camera images (12800 frames/s) of the formed plasma elucidate the ionization of an axially propagating plasma. Long-exposure images (1.3 s) capture the full propagation distance of the plasmoid. Rogowski coil current diagnostics elucidate the timing of a self-crowbar discharge that delineates between deflagration and snowplow modes. An empirically determined 50-ms gas puff duration resulted in a maximum plasma propagation distance of $\approx 23$ cm. Shorter durations did not ionize a sufficient amount of gas for elongated axial propagation, whereas longer durations suppressed axial plasma sheath expansion. This type of gas injection CPG device is now qualified for use in CPG experiments that require the snowplow mode and maximum mean free path of fast ions resulting from various plasma heating mechanisms. These include CPG operation within external magnetic fields in which significant plasma propagation distance is required, including solar physics experiments and space propulsion development. [ABSTRACT FROM AUTHOR]

We report the deposition of nanocrystalline graph- itic films on Cu foil in a roll-to-roll (R2R) plasma-enhanced chemical vapor deposition (PECVD) system. The influence of discharge modes on the graphitic film synthesis is studied in radio frequency (RF) capacitively coupled Ar/H2/CH4 plasma. First, electrical and spectroscopic characterizations supported with modeling are carried out to study the properties of hybrid and gamma modes in Ar plasma at an excitation frequency of 80 kHz. A hybrid mode, which exhibits both alpha and gamma characteristics, exists at 950 Pa for Ar plasma at powers up to 1100 W. However, Ar plasma transitions at 1380 Pa from hybrid to gamma mode when the power is greater than 750 W. Second, the quality of the nanocrystalline graphitic films, which is assessed with Raman spectroscopy, is correlated with the characteristics of hybrid and gamma modes in Ar/H2/CH4 plasma. The hybrid mode in Ar/H2/CH4 plasma has relatively less ion bombardment. However, the gamma mode in Ar/H2/CH4 plasma provides abundant intermediate carbon species and heats the Cu substrate directly to around 1193 K. Hence, thin films of nanocrystalline graphite with different qualities can be produced at a web feed rate of 30 mm/min without supplemental heating by adjusting the discharge modes. [ABSTRACT FROM AUTHOR]

We present an experimental analysis of the change in the electric field enhancement factor with varying gap size and penetration depth (P.D) of cathode into anode for a coaxial vacuum gap, diagnosed using Fowler–Nordheim analysis and optical imaging via scanning electron microscope (SEM) and time integrated Digital single lens reflex camera (DSLR). Data were collected on the Coaxial Gap Breakdown Machine (240 A, 25 kV, 150 ns, ~0.1 Hz). Experiments using five different gap sizes at nine different P.Ds are compared over runs comprising 50 shots for each case. The results show a strong link between enhancement factor and gap size, with P.D and surface topology. For large gap sizes, 150, 330, and 700 $\mu \mathrm {m}$ , the average enhancement factor value increases with increasing P.D. For smaller gap sizes, 50 and 100 $\mu \mathrm {m}$ , the average enhancement factor decreases with P.D. SEM imaging before and after plasma formation for each gap size allows for quantifying surface finish, microprotrusion growth, average blast diameter, and an estimation of the surface area breakdowns occupy. Time integrated DSLR imaging analysis of the gap at each shot allows for a determination of the distribution of breakdowns about the circumference of the gap for each case tested. The Fowler–Nordheim analysis allows for a quantitative analysis of the surface roughness of all gap sizes tested. Results show that for large gap sizes, the gap geometry and increasing area of breakdown is the main cause for increasing average enhancement factor. For small gap sizes, the dominant driving factor for small average enhancement factors—that subsequently decrease with P.D—is significant changes in surface topology due to an increased number of breakdowns. [ABSTRACT FROM AUTHOR]

This study explores the degradation of the reactive Remazol Blue RR (RBRR) as a model textile effluent upon its exposure to non-thermal atmospheric pressure plasma. An extensive comparative study of different combinations of the following plasma/solution treatment environments was conducted: 1) Ar plasma jet (Ar-PJ) alone; 2) Ar/O2 and Ar/N2 plasmas; 3) Ar plasma with O2 or N2 injected (INJ) in the bulk of the Ar plasma afterglow; and 4) Ar plasma with O2 or N2 bubbling (BB) in the RBRR solution. In all conditions, plasma treatment was carried out at a fixed applied voltage of 31 kV and treatment time of 10 min. The degradation efficiency of RBRR in the different plasma-treated solutions was evaluated using UV–visible spectroscopy. Optical emission spectroscopy (OES) was used to examine the generation of excited species in plasma during the degradation processes. Moreover, the concentration of plasma-induced reactive hydroxyl radicals (OH•) and hydrogen peroxide (H2O2) was determined spectroscopically. To further corroborate the results, the pH, conductivity, and total organic carbon (TOC) of the plasma-treated RBRR solutions were assessed. Overall, the results showed that the highest degradation efficiency (45%) was obtained upon exposure of RBRR aqueous solution to Ar plasma with N2 bubbling in the solution. The non-toxic nature of all plasma-treated solutions was confirmed by non-inhibition of bacterial growth (Escherichia coli and Staphylococcus aureus). Overall, plasma treatment in general and Ar plasma accompanied with N2 bubbling in particular constitute an eco-friendly and very promising techniques to degrade/decolorize textile effluent. [ABSTRACT FROM AUTHOR]

This work reports the estimation of discharge diameter ($d_{d}$) using “Gaussian fit” method applied on the discharge’s image captured using high–speed camera (HSC). Work was conducted in a rotating gliding arc (RGA) and obtained the $d_{d}$ near the shortest ($\delta $) and longest ($\Delta $) gap between the electrodes, operated under 5 SLPM (transitional) and 50 SLPM (turbulent) flow rates of argon gas at atmospheric conditions. Gaussian fit was verified to be suitable to estimate the thickness of the objects that could be well differentiated from the background in the captured image. Furthermore, the results indicated that the gas flow rate is highly influential on $d_{d}$. The average $d_{d}$ was thinned by ≈28%, from 0.29 to 0.21 mm, when the flow rate was increased from 5 to 50 SLPM, indicating the influence of turbulent eddies at 50 SLPM. The $d_{d}$ was varying along the discharge length under turbulent flow due to discharge’s inhomogeneity in intensity arising due to twisting, curling, and knot formations. This work marks an essential step toward the characterization of the RGA reactor. [ABSTRACT FROM AUTHOR]

The plasma limiter (PL) is a suitable method to protect electronic devices from high-power electromagnetic pulses. The $S$ -band PL has target specifications of 100 kW of power handling capability, < 100 ns of response time, and < 0.5 dB of insertion loss. Carbon nanotube (CNT) can be used to reduce power losses and instrument corrosion under frequent electromagnetic attacks. This article used CNT-coated copper needles in a PL to increase the electric field for the rapid breakdown process. Furthermore, the impact of dimensional parameters (needle’s length, needle’s radius, and axial displacement of the needles) were investigated. The experiment was conducted at 1800 W of peak power and 25 ns of the $S$ -band (2.45 GHz) microwave duration. In this case, the height of 19 mm and diameter of 1 mm were found to be the optimal needle parameters, in which the fastest breakdown of the electric field is available. The finite-element method was used by CST software to verify the experiment results. The transmission losses were < 5% in the normal state. The breakdown electric field threshold was ~431 kV/m near the atmospheric pressures. There was an error of < 1.28 in the case with the lowest compatibility. [ABSTRACT FROM AUTHOR]

In this study, voltage distribution and surface dielectric barrier discharge (DBD) of a microplasma discharge device (MDD) were modeled in 2-D domain using finite-element analysis (FEA). Initially, the voltage distribution across comb-, H-tree-, and honeycomb-structured MDD was analyzed. Then, the cross section of an MDD consisting of a polyimide-based dielectric sandwiched between two copper electrodes was used for modeling the microplasma discharge characteristics in an argon environment. A sinusoidal voltage was applied to one of the copper electrodes while the other electrode was grounded. The spatial distributions of electron temperature (ET) across the electrodes for varying input voltages were simulated to demonstrate the importance of breakdown voltage. A detailed analysis on the effect of varying electrode and dielectric barrier thicknesses on electron density and ET was also performed to understand the importance of optimizing device configurations for microplasma discharge. Moreover, MDD was also simulated in varying ambient temperature and pressure conditions to evaluate their effect on ET and density across the electrodes. The results from these simulations provide a better understanding of parameters such as varying input voltage, electrode, and dielectric thickness on ET and electron density. This enables us to optimize design parameters for fabricating MDDs and the operating conditions for effective sterilization applications. [ABSTRACT FROM AUTHOR]

This article presents the complete design of a hybrid metal-plasma transmit-array antenna with beam-scanning capabilities. The antenna operates at 1.07 GHz and consists of an active metallic dipole, a metallic ground plane (GP), and a set of cylindrical plasma discharges arranged in a 2-D lattice. The main lobe of the antenna can be tilted toward different directions simply by turning on/off specific subsets of plasma discharges. Toward this aim, a two-step optimization strategy based on the combination of a particle swarm optimization (PSO) and of a genetic algorithm (GA) is adopted. A realistic model of the antenna has been simulated in CST Microwave Studio. To derive plasma parameters, a prototype plasma discharge has been realized and tested. Each plasma bar included in the numerical setup comprises not only the plasma material, but also the glass envelope and the metallic electrodes used to confine and generate the plasma, respectively. An analysis has been carried out to evaluate the effects of adding the electrically long metallic cables to each discharge needed to ignite and sustain the plasma. The radiation properties of the array can be maintained thanks to the insertion of inductances between the electrodes and the cables. Finally, a sensitivity analysis has been conducted to identify intervals of plasma density and neutral gas pressure within which the beam-scanning capabilities of the antenna remain unaffected. [ABSTRACT FROM AUTHOR]

As energy storage elements in modular multilevel converter (MMC) sub-module of a unified power flow controller (UPFC), metallized film capacitors endure ac and dc superimposed voltages, which brings new challenges to insulation performance of the dielectric film. In this article, an experimental setup was created to investigate the breakdown characteristics of the dielectric film for sub-module capacitors. Factors which may affect breakdown strength under ac and dc superimposed voltages were studied experimentally. The results reveal that, as the dc voltage component increases in the range of 0–3200 V, the breakdown strength gradually increases by 16.36%; as the ac voltage component increases in the range of 0–1800 V, the breakdown strength slightly decreases by 3.52%; the breakdown strength is more affected by frequency as the ac voltage component increases and decreases with increasing frequency; as temperature increases from 20 °C to 95 °C, the breakdown strength substantially decreases by 31.12%; as the thickness of the film increases from 7 to $10~\mu \text{m}$ , the breakdown strength slightly increases by 6.32%. For capacitors in 500-kV UPFC, the dc voltage component is approximately 1600 V; the ac voltage component, whose peak-to-peak value is within 800 V, mainly contains power frequency and the second harmonic components. According to the experimental results, since the ac voltage component is small and the order of harmonic is low, the breakdown strength of capacitors in UPFC has little difference compared with that of the dc capacitors. This article can provide a reference for insulation design optimization of capacitors in UPFC. [ABSTRACT FROM AUTHOR]

A 4-MV self-triggered switch based on ultraviolet (UV) illumination technology is designed and tested under approximate 800-ns rise time pulse voltage. The switch is composed of five sections in series, and each section comprises an UV-illuminating gap (UV gap) and a main gap. The voltage charged on the UV gap is obtained by a resistance–capacitance coupling circuit, which enhances synchronization with the main gap voltage. The gap distance of the 4-MV switch is determined according to the performance of the same type of switch under a shorter pulse (about 300 ns), while the characteristics of the gap under 800-ns pulse voltage is still unclear. The experimental results show that low jitter breakdown of the switch can be realized effectively when two UV gaps are functioning. The breakdown jitter percentage achieves less than 1.55% within the range of 1.0–3.2 MV. When the working scope is narrowed down to 1.4–2.1 MV, the breakdown jitter is less than 1%. [ABSTRACT FROM AUTHOR]

A surface corona actuator for flow control, already tested in wind tunnel experiments, is here characterized at the bench in still air. The anodic electrode is provided with periodic triangular tips and is operated with a pulsed waveform. The operating stability and voltage range turn out to be wider than for dc operation. The actuator is characterized by means of several measurements as a function of the frequency, including power absorption and ionic wind measurements in different locations. The ionic wind is measured first by a micropitot probe obtaining time-averaged values, then by a hot wire anemometer obtaining instantaneous velocities and turbulence spectra. The behavior of the actuator is interpreted accounting for the creation and removal of charges in the gap subject to a periodic excitation. [ABSTRACT FROM AUTHOR]

Surface dielectric barrier discharges (SDBDs) at atmospheric pressure can be achieved by direct air discharge. It can produce reactive species without expensive vacuum chambers as well as generate the ionic wind to control the airflow or accelerate actuators. For the purpose of extending the discharge zone to satisfy the larger area treatment of materiel or enhance the electrohydrodynamic (EHD) force, an efficient way is to arrange several single modules of SDBDs in series. In this article, several kinds of SDBDs with different geometries and voltage polarities of multi-electrode are studied to investigate the discharge dynamical characteristics, such as the discharge uniformity, the streamer length, the number of streamers, and the EHD force during the discharge. The spatial distribution of the electric field (or potential gradient) established by the electrode array is crucial to determine the discharge behaviors. [ABSTRACT FROM AUTHOR]

In this article, a nonthermal gliding arc discharge (GAD) was generated in an air flow driven by a 40-kHz alternating current (ac) constant-current electric power supply. The influence of gas flow rate on the discharge characteristics of gliding arc was investigated using electrical diagnostics and fast Fourier transform (FFT) analysis method. The average discharge power, total harmonic distortion rate of arc voltage (THD ${_{u}}$), total harmonic distortion rate of arc current (THD ${_{i}}$), and the resistance of arc were experimentally studied. As the air flow rate increased from 4 to 12 L/min, it was found that the average discharge power of the gliding arc gradually decreased from 407.9 to 187.8 W. However, because of the nonlinear characteristics of the GAD circuit, with air flow rate increasing, both THDu and THDi linearly increased, while the resistance of arc gradually decreased from 26.3 to 14.1 $\text{k}\Omega $. Totally, the air flow rate influenced the discharge characteristics of the gliding arc mainly by ruling the average discharge power. Finally, for a better understanding of the discharge characteristics of the gliding arc, a discharge circuit model was further analyzed based on the average discharge power and reactive power. [ABSTRACT FROM AUTHOR]

Simple low-temperature pulsed power dissociation method for high resistive liquid is proposed in this article. Active high voltage rebound tailing pulse (RTP) diodes are adopted to conventional high voltage pulse power sources. In order to explain this method, the study was performed using deionized water (DIW) (high resistive $>17~\text{M}\Omega \cdot $ cm) electrolysis with two immersed electrodes. The forward pulses, the full-width at half-maximum (FWHM) of 400 ns and forward voltage (7 kV) with rising-up ratio (dV/dt) of 1011 V/s, were applied to the electrodes. When a 5 kV RTP diode was simply adopted to this electrical circuit and DIW load in series, the high forward voltage pulse and continuous high reverse current were applied to this circuit. Then, H2 was generated at the anode electrode and OH radical (OH) in the water vessel. Those phenomena were apparently dependent on the anode electrode area. At the beginning of the forwarded high voltage application, the circuit behaved as capacitance load with generated ions and built up charges at the interface between DIW and the electrode. Continuous rebounded high reverse voltage and highly built-up reverse recovery charges induce avalanche breakdown of RTP diode. The rebounded electrical current was found to be collected in the circuit, accompanied by the generation of hydrogen and OH, as well as the tailing current flowing at the interface as a resistive load. In consequence, we point out that rebounded electrons injected from the surrounding water to the anode electrode interface induced the water electrolysis characteristically, according to RTP-diode inserted in the circuit. [ABSTRACT FROM AUTHOR]

This article describes the performance of a multi-gap, multichannel (MGMC) spark gap switch, evaluated numerically and experimentally, to achieve multichanneling using a relatively low-magnitude trigger pulse. First, an electrostatic analysis of the switch geometry was carried out using COMSOL Multiphysics 5.5 to determine the electric field distribution during high-voltage hold-off before triggering and to determine the coupling parameters between trigger and other intermediate electrodes of the switch. Second, a circuit model was developed in PSpice Lite 16.6 for predicting the process of channel formation and its influence on adjacent channels. Based on the simulation results obtained, a six-gap, eight-channel, planar MGMC switch operating in air has been designed and developed. The developed switch was, then, incorporated into a compact experimental setup to experimentally evaluate various switch parameters such as inductance, switching delay, jitter, and closing time when triggered using a negative-polarity trigger pulse of magnitude −40 kV, generated using a compact, in-house developed trigger generator. In contrast to most of the reported MGMC switches that use complicated Marx-based generators to produce ≥120-kV trigger pulses for multichannel formation, the experimental results, thus obtained, report comparable switch performance using a low-magnitude (−40 kV) trigger pulse. In addition, framing and streak camera images taken during the current discharge indicate the presence of ~6 luminous channels. In addition, short-circuit experiments for estimating switch inductance by consecutively shorting one or more channels also indicate multichanneling in the switch using a low-magnitude trigger pulse. [ABSTRACT FROM AUTHOR]

A coaxial electrode configuration with surface dielectric barrier discharge is designed to generate a cold plasma jet emerging into the ambient air. A technique to determine the length of plasma extension based on the measurements of average values of current and applied voltage is proposed. The capacity of the discharge cell calculated using current and voltage values agrees with the capacity obtained from the integral length of a plasma layer along a dielectric surface. The average charge deposited on the dielectric surface is determined. [ABSTRACT FROM AUTHOR]