Pulsed DC Power Supply Research Articles

Effect of pressure and current density on metastable argon dynamics in low-pressure Ar-O2 plasma

Abstract Non-thermal plasma demonstrates a significant enhancement in efficiency when oxygen is added into the plasma mixture, particularly in processes such as thin-film oxide deposition, poly film removal, and photoresist mask ashing. This study examines the behavior of metastable argon states (1s5 and 1s3) in Ar-O2 mixture plasma, generated by a 50 Hz pulsed DC power supply under low-pressure conditions ranging from 1 mbar to 7 mbar. The densities of metastable argon states were assessed at varying conditions of current density, argon concentration, and filling gas pressure, utilizing optical emission spectroscopy (OES). The argon emission line ratio technique was employed to determine the plasma parameters. Experimental results indicate that electron density increases with current density, driven by enhanced excitation and ionization processes, while higher argon concentrations facilitate efficient ionization. The declining trend of the electron density with an increase in filling gas pressure is attributed to higher-pressure collisional processes. Metastable argon atoms exhibit heightened density with increased current density and argon percentage but decrease with elevated pressure due to loss processes. The regulation of metastable states is crucial for processes like etching, surface modification, and sterilization, providing a crucial step to the optimization and enhancing these applications.

Low-frequency harmonic current suppression for a dc pulsed power supply based on improved ADRC

Low-frequency harmonic current suppression for a dc pulsed power supply based on improved ADRC

Mechano-synthesized wollastonite-forsterite composite coatings on the plasma electrolytic oxidized Ti-6Al-4V alloy for dental implant

This study investigated an innovative approach for dental implant coatings by developing mechano-synthesized wollastonite-forsterite composite coatings (MC) on plasma electrolytic oxidized (PEO) Ti-6Al-4V alloy. The process involved PEO treatment using a pulsed DC power supply in an electrolyte solution of mono-calcium acetate and calcium glycerophosphate, followed by MC with mixed wollastonite (CaSiO3) and forsterite (Mg2SiO4) powders. After MC treatment, FESEM, EDS analysis, cross-section, XPS, Raman analysis, corrosion test, and an in vitro test for biocompatibility were performed. Comprehensive surface characterization revealed that wollastonite particles transformed into smaller needle-like shapes, while forsterite particles became slightly less uniform but retained their spherical shape. Higher wollastonite content resulted in greater pore filling with fine particles, whereas increased forsterite content led to fewer fine particles on the surface. Cross-sectional analysis showed Si concentration inside the pores. Notably, wollastonite-rich samples exhibited superior corrosion resistance and rapid initial apatite formation in simulated body fluid (SBF) studies. In contrast, forsterite-containing samples demonstrated more controlled and sustained bioactivity, forming magnesium-substituted hydroxyapatite over time. The novelty of this work lies in combining the bioactive properties of wollastonite and forsterite with enhanced PEO surface characteristics, resulting in coatings with tailored corrosion resistance and bioactivity profiles suitable for dental implant applications.

Mechanical octacalcium phosphate coatings on the plasma electrolytic oxidized pure titanium for bio-implant use

In this study, OCP powder was used for mechanical coating on the plasma electrolytic oxidized (PEO) implant surface to improve bioactivity. PEO treatment was performed on the surface of the implant using a solution mixed with calcium acetate and calcium glycerophosphate, and creates porosity through a pulsed DC power supply. For compositional analysis, energy dispersive X-ray spectrometer analysis was employed to calculate OCP content and X-ray diffractometer analysis was used to confirm the crystal structure. Also, wettability, surface roughness, hardness, elastic modulus, and corrosion resistance testing were performed. Significantly, the reduction in OCP particle size decreased, and pore filling with OCP smaller particles increased as mechanical coating time increased from 0 to 12 h. Surface and cross-sectional morphology showed the presence of OCP on the substrate. Also, surface roughness, contact angles, hardness, and elastic modulus were reduced as mechanical coating time increased. Corrosion resistance was found to be the highest for mechanical OCP coating for 6 h surface treatment on the PEO-treated CW-Ti.

Fabrication and Electrical Characterization of p/n PbSe Diodes

Lead selenide (PbSe) diodes were fabricated using a magnetron sputtering process system with a pulsed DC power supply and a 2-inch PbSe target with a purity of 5N. For p-type PbSe thin films, the process variable was the oxygen ratio in the mixed gas of argon and oxygen. The electrical characteristics of the thin films were observed after heat treatment. For the n-type PbSe, nickel (Ni) was used as a doping material. The deposition and doping were performed simultaneously using a co-sputtering method. During co-sputtering, the input power of the Ni sputter gun was adjusted as a process variable. Hall measurement experiments were performed to measure the doping concentration and resistivity of both the p-type and n-type PbSe semiconducting films. The maximum doping concentration was 2.33×10<sup>19</sup> cm<sup>-3</sup> for p-type PbSe and 7.55×10<sup>20</sup> cm<sup>-3</sup> for n-type PbSe thin films, respectively. The p-n junction IV curve showed that the lowest forward voltage generation point, V<sub>f</sub>, was 1.5 V and the reverse breakdown voltage was -4.3 V. In the photocurrent measurement, the photo sensitivities of the heat-treated samples were higher than that of the non-treated sample, and the maximum value was 5.148. Photo responsivity was also higher in the heat-treated samples. Its maximum was 0.7306 mA / W.

Improved creep resistance of AZ91 magnesium alloy after the micro arc oxidation process

AZ91 Mg alloy has a wide range of applications in the automotive industry, although its use is restricted to powertrain applications due to its low creep resistance. In this study, the effect of the micro arc oxidation (MAO) coating on the creep resistance of an AZ91 Mg alloy was investigated to take advantage of the coating layer with high thermal insulation properties. In this context, the MAO process was applied to AZ91 Mg alloy using a bipolar pulsed DC power supply. The creep tests were conducted at different temperatures (150–200 °C) and stresses (25–90 MPa) for the bare and coated samples, and the minimum creep rates were determined. It has been shown that the MAO coating reduces the creep rate of the bare alloy by 35%–84% depending on the temperature and the stress due to the stress-reducing effect and thermal barrier properties of the MAO coating. Based on the calculated creep activation energy and stress exponents, creep mechanisms were proposed for the bare and coated alloys. Effective activation energy was also calculated and lattice diffusion-controlled dislocation climb was determined to be the effective creep mechanism for both samples at lower stresses, while pipe diffusion-controlled dislocation climb was effective at higher stresses.

Contrasting the characteristics of atmospheric pressure plasma jets operated with single and double dielectric material: physicochemical characteristics and application to bacterial killing

This study reports an experimental comparison of two types of atmospheric pressure plasma jets in terms of their fundamental plasma characteristics and efficacy in bacterial sterilization. The plasma jets are fabricated by inserting a high voltage electrode inside a one-end closed (double DBD plasma jet) or both ends open (single DBD plasma jet) quartz tubes which are further enclosed inside a second quartz tube containing a ground electrode. Both plasma jets are operated in contact with water surface by using a unipolar pulsed DC power supply with helium as the working gas. Results from electrical and time-resolved imaging show that the single DBD configuration induces 3–4 times higher accumulation of charges onto the water surface with significantly faster propagation of plasma bullets. These results are accompanied by the higher discharge intensity as well as stronger emissions from short-lived reactive species which were analyzed through optical emission spectroscopy at the plasma-water interface. The rotational temperature for the single DBD configuration was observed to be higher making it unsafe for direct treatments of sensitive biological targets. These characteristics of the single DBD configuration result in the production of more than two times higher concentration of H2O2 in plasma activated water. Shielding of the HV electrode reduces the plasma potential which in turn reduces the electric field & electron energy at the plasma-water interface. The reduced electric field for the double DBD configuration was lower by ≈463 Td than the single DBD configuration. The bactericidal efficacy of the two configurations of the plasma jets were tested against Escherichia coli, a well studied Gram-negative bacterium that can be commensal and pathogenic in human body. Our results demonstrate that although single DBD plasma jet result in stronger antibacterial effects, the double DBD configuration could be safer.

Study of the influence of a gradient gas flow as an alternative to improve the adhesion of Diamond-Like Carbon film in the wear and corrosion resistance on the nitrided AISI 4340 steel

Diamond-Like Carbon (DLC) films have been widely studied due to their interesting properties, but this film presents low adhesion on metal surfaces. Interlayers have been performed, between the substrate and the DLC film, combined with previous surface treatment as plasma nitriding to improve film adhesion on the surface. This work aims to develop a multilayer treatment of nitriding, gradient treatment, and DLC film deposition without organosilicon interlayer to determine the synergic influence of treatments on multilayer adhesion, wear, and corrosion resistance of the AISI 4340 steel. Plasma surface treatments such as simple nitriding, simple DLC film deposition, which consists of treatments performed individually, multilayer treatment of nitriding + DLC with and without an organosilicon interlayer, and multilayer treatment of nitriding + gradient treatment + DLC without interlayer using gas flow gradient were carried out using a pulsed-DC power supply. The highest wear and corrosion resistance was obtained by the multilayer treatment with organosilicon interlayer due to the synergic effect of this interlayer with the DLC film and nitriding treatment, but the multilayer treatment without organosilicon interlayer performed with gas flow gradient presents better corrosion and wear properties compared with simple treatment. Results have shown that it is possible to perform multilayer treatments with the presence and the absence of an organosilicon interlayer, keeping wear, corrosion, and adhesion properties of the DLC film on nitrided AISI 4340 steel deposition.

Experimental Investigation into Residual Stress in Ball End Magne-Torheological Finishing

Ball end magnetorheological finishing (BEMRF) is a novel finishing process used to finish variety of surfaces ranging from flat, curved, complex, two dimensional, three di-mensional and non linear. The residual stress and surface finish play an important role in overall efficiency and durability of the components. The present work is aimed to relieve the residual stress of work-piece surface with the improvement in surface finish using pulse DC power supply (PDCPS) in BEMRF process. The preliminary experiments have been conducted on flat EN-31 steel with and without pulse DC power supply (WPDCPS). The process parameters during experiments were considered as magnetiz-ing current (MC) of 2.5A, tool rotational speed (TRS) 500 rpm, and working gap (WG) 1.5 mm with finishing time 35 minutes and 55 mm/minute feed rate given to the work-piece. The responses such as residual stress and surface roughness have been measured before and after experimentation. Residual stress of EN-31 surface was measured with X-ray residual stress analyzer using Cosα method. It has been observed that the residual stress was found reduced from 130 to 66 MPa and surface roughness was reduced drastically wit h the use of pulse DC power supply in BEMRF process. After preliminary experi-mentation, the statistical analysis with design of experiment has been conducted with pulse DC power supply on EN-31 steel to visualize the effect of various process parame-ters on residual stress using RSM technique.

Electrical Properties of Aluminum Nitride Thick Films Magnetron Sputtered on Aluminum Substrates.

The realization of a c-axis oriented aluminum nitride thick film on aluminum substrates is a promising step in the development of transducers for applications with a working temperature up to about 600 °C. The present paper deals with the realization of AlN thick films by means of reactive magnetron sputtering with a pulsed DC power supply, operating in continuous mode for 50 h. Two values (0.4 and 0.8) of nitrogen concentration were used; operative pressure and power were set at 0.3 Pa and 150 W, respectively. The thickness of the obtained aluminum nitride films on the aluminum substrate, assessed with a profilometer, varied from 20 to 30 µm. The preferential orientation of AlN crystals was verified by X-ray diffraction. Finally, as the main focus of the investigation, the films underwent electrical characterization by means of an LCR-meter used on a parallel plate capacitor set-up and a test system based on a cantilever beam configuration. AlN conductivity and ε33 permittivity were derived in the 100 Hz–300 kHz frequency range. Magnetron sputtering operation with nitrogen concentration equal to 0.4 resulted in the preferred operative condition, leading to a d31 piezoelectric coefficient, in magnitude, of 0.52 × 10−12 C/N.

Study of the Effect of Nitrogen on Corrosion, Wear resistance and Adhesion Properties of DLC Films Deposited on AISI 321H

The deposition of DLC films on 321H stainless steel aims at attributing properties such as high wear resistance and low friction coefficient to the substrate material. Nitrogen added to DLC can improve the film adhesion to metal substrates, but the investigation of its effect on corrosion resistance, an important property for stainless steels, is lacking. The DLC film was deposited by plasma-enhanced chemical vapor deposition (PECVD) using a pulsed-DC power supply with a gas mixture of Ar and CH4, and to the DLC(N) film deposition was used CH4 and N2 varying the percentage of nitrogen from 10 to 50% in the treatment. DLC films improved both the wear and corrosion resistance of 321H stainless steel. The results show that the 10, 20 and 30% of N2 supply during the deposition increased the adhesion of the film on the substrate, enhancing the wear resistance of the treated material. The addition of 40 and 50% of N2 during the deposition, however, impaired the corrosion resistance compared with the substrate. An improvement of adhesion, wear and corrosion resistance were observed for 30% N2 condition. Thus, the incorporation of suitable concentration of nitrogen modifies the features of the DLC film, obtaining a good combination of high wear resistance and corrosion protection due to a combination of structure, high thickness, and high adhesion of the film to 321H stainless steel.

Generation of high aspect ratio complex micro-features by micro-electrochemical milling employing novel flushing technique

Fabrication of high aspect ratio (HAR) complex micro features on high strength temperature resistant (HSTR) alloys is challenging by any conventional or non-conventional machining methods. In this study blind, HAR and complex micro features have been fabricated by micro electrochemical milling (MEM) on HSTR Cobalt alloy (Haynes-188) introducing a new strategic approach with novel flushing technique which could get rid of the need of pulsed DC power supply. Multiphysics simulation of the rotating micro-tool at different rpm and its impact on effective sludge removal has been analyzed and verified experimentally. In this study, most influencing parameters of MEM like voltage, feed rate, rpm of tool and milling layer depth have been selected to investigate their effects on the machining responses like width overcut, machined depth and surface roughness on Haynes-188 alloy. Comparison has also been made with constant and pulsed DC power source to know the influence of these process parameters on the MEM responses. Finally, several linear and non-linear blind, HAR (AR > 11) and intricate micro features have been fabricated successfully on cobalt alloy at the most suitable parametric combination, i.e., 7.5 V of machining voltage, feed rate of 0.3 mm/min, and tool rotation of 750RPM with 0.5 M of NaNO3 electrolyte.

Pulsed Discharge Plasma in High-Pressure Environment for Water Pollutant Degradation and Nanoparticle Synthesis

The application of high-voltage discharge plasma for water pollutant decomposition and the synthesis of nanoparticles under a high-pressure argon gas environment (~4 MPa) was demonstrated. The experiments were carried out in a batch-type system at room temperature with a pulsed DC power supply (15.4 to 18.6 kV) as a discharge plasma source. The results showed that the electrode materials, the pulsed repetition rates, the applied number of pulses, and the applied voltages had a significant effect on the degradation reactions of organic compounds. Furthermore, carbon solid materials from glycine decomposition were generated during the high-voltage discharge plasma treatment under high-pressure conditions, while Raman spectra and the HRTEM images indicated that titanium dioxide with a brookite structure and titanium carbide nanoparticles were also formed under these conditions. It was concluded that this process is applicable in practice and may lead to advanced organic compound decomposition and metal-based nanoparticle synthesis technologies.

The effect of cold plasma on antioxidant enzymes, minerals, and some of the levels of the biochemical parameters in the subjects with type 2 diabetes mellitus samples

Introduction: Hyperglycemia in people with diabetes mellitus and its lack of control are associated with irreversible consequences. Glycation of proteins and enzymes, especially antioxidant enzymes in uncontrolled diabetes mellitus, affects these consequences. Consumption of bioactive compounds containing antioxidants and minerals as well as the use of adjunct therapies, such as cold atmospheric plasma therapy, can be effective in preventing and controlling the consequences of diabetes mellitus.Objective: In this research, we investigated whether cold plasma treatment of diabetic samples was effective in altering the activity of oxidative enzymes, some biochemical elements, and biochemical parameters.Methods: Thirty individuals with type 2 diabetes mellitus and 30 healthy individuals, as controls, participated in the study. The samples were exposed to cold argon plasma jet for 10 minutes (by a 10 kHz pulsed DC power supply with an amplitude up to 20.0 kV). The following contents of the serum samples of all participants were evaluated according to the instructions of the used kits before and after the cold argon plasma jet treatment: the activity of catalase, superoxide dismutase, and glutathione peroxidase enzymes; the concentration of glucose, hydrogen peroxide, and selenium binding protein 1 (as an indicator of blood selenium); and the concentration of copper, zinc, iron, and magnesium.Results: The activity of antioxidant enzymes and minerals significantly increased in diabetic samples treated with cold plasma (P value < 0.05). No significant changes were observed in the concentrations of glucose, hydrogen peroxide, or selenium binding protein 1 in diabetic samples treated with cold plasma.Conclusions: Using cold argon plasma jet as an adjunct method, which will reduce the glycation of enzymes and improve some minerals, can reduce the risk of diabetes complications in patients with diabetes mellitus.Keywords:Antioxidant enzymes, Cold plasma, Diabetes mellitus, Minerals.

Influence of Various Pulse Waveforms during Fabrication of Micro Rectangular Pattern by Masked Tool using Electrochemical Micromachining

Maskless electrochemical micromachining (EMM) is an alternative method to fabricate microsurface textures on conductive substances, but it is still very challenging issue to create microsurface textures by this method. This paper proposes a new issue that maskless EMM process generates micro rectangular patterns using various pulse waveforms i.e. triangular, sine and square of pulsed DC power supply at constant voltage mode on stainless steel (SS-304) workpiece. A novel concept of maskless EMM setup consisting of EMM cell, electrode holding devices, electrical connections and vertical cross flow electrolyte system is introduced for the generation of high-quality micro rectangular patterns using various pulse waveforms. Another important finding is that SU-8 2150 negative photoresist can fabricate more than 28 micro rectangular patterned samples with higher dimensional accuracy and surface quality. The influence of machining voltage, inter electrode gap, pulse frequency, duty ratio and flow rate is investigated on machining performance such as length overcut, width overcut, machining depth and surface roughness ([Formula: see text] of micro rectangular pattern using three pulse waveforms. One mathematical model is developed to show the effectiveness of three pulse waveforms by the estimation of current efficiencies. From the experimental investigation, it is observed that higher frequency with square waveform at constant duty ratio is suitable to generate high-quality micro rectangular patterns under pulsed DC power supply.

The Production Efficiency of Reactive Oxygen and Nitrogen Species (RONS) of AC and Pulse-DC Plasma Jet

Atmospheric pressure plasma jets driven by ac and pulsed-dc voltage were characterized, operating in helium with different admixture fractions up to 2% pure air, N2, and O2. The absolute production efficiency of nitrogen dioxide, nitric oxide, ozone, hydroxyl, and atomic oxygen was measured when plasma was processing real biological tissue. The power consumption of each power source, the effect of frequency, and gas composition were investigated. It has been found that the power consumption of 10-kHz ac-driven plasma jets increases with gas mixture increasing from 0% to 0.5% and then decreases slightly with gas mixture increasing from 0.5% to 2.0%, while 1-kHz ac-driven plasma jets are almost constant. Moreover, the average dissipated power of 10-kHz ac-driven plasma jets was about ten times more than that of the 1-kHz case, while the power consumption of P-dc-driven plasma jets was not drastically affected by gas admixture. Furthermore, O2 and air were important impurities contributing to the O, O3, and NO2 production efficiency, while N2 admixture would enable the diminution of O and O3 production efficiency. Especially, an admixture of O2, N2, and air to the main helium flow led to a reduction of OH and NO production efficiency for both ac and pulsed-dc power supply. This research may prove to be valuable both for an attainable range of RONS production efficiency and plasma medical research as a tool for assigning specific RONS or RONS mixtures.

Fabricating a Raman spectrometer using an optical pickup unit and pulsed power

Although Raman spectroscopy is a major analytical tool in modern chemical experiments, commercial Raman spectrometers remain very pricey for educational and research purposes in individual university laboratories. Thus, this study focused on the structural similarity between the Raman spectrometer and an optical pickup unit (OPU), which is an inexpensive compact optical device used for a part of optical discs. The study investigated whether or not a full set of Raman spectrometer can be developed at a cost of less than 1,000 US$. The OPU-based Raman spectrometer was fabricated using 3D printer-made components, a Raman edge filter, and a laser diode with a wavelength of 520 nm as the light source. A function generator was used as a pulsed power source to analyze the characteristics of the OPU Raman spectrometer according to various frequencies and duty ratios. When using a pulsed DC power supply, the laser wavelength tended to move to a longer wavelength with increases in duty ratios. That is, the higher the frequency at the same duty ratio, the weaker the background light intensity compared with the scattered Raman signal intensity. The findings illustrate that Raman signal strength can be adjusted by adjusting the focal length of the objective lens of the OPU through an external adjustment of an additional DC power. In the Raman spectra of all solid and liquid samples used, the maximum error rate reached approximately 11 cm−1, whereas the maximum intensity deviation reached approximately ± 6%. The cost of the complete OPU Raman spectrometer is less than 1,100 US$ using a function generator as power source and less than 930 US$ using a DC adapter. If the optical density (OD) 6 filter can be replaced with the OD 4 filter, then the costs are expected to decrease to approximately 730 US$.

A Study for the Nanofinishing of an EN-31 Workpiece with Pulse DC Power Supply Using Ball-End Magnetorheological Finishing

Ball-end magnetorheological finishing (BEMRF) is a high-level nanofinishing process used in finishing different kinds of surfaces including flat, 2- and 3-dimensional, and curved surfaces. In the present study, a pulse DC power supply is used to energize the electromagnet of magnetorheological (MR) finishing tool. The experiments have been conducted on EN-31 flat workpiece surface with and without pulse DC power supply using a magnetizing current (MC) 2.5 A, a working gap (WG) of 1.5 mm and a rotational speed of the tool (RST) of 500 rpm with a feed rate of workpiece of 50 mm/min. The study has been carried out to analyse the effect of the duty cycle on the response percentage reduction in surface roughness. It has been observed that an improved response percentage reduction in surface roughness has been found with pulsating DC power supply as compared to the response percentage reduction in surface roughness obtained with DC power supply without pulse at the same process parameters. After conducting the preliminary experiments, the statistical analysis was done to analyse the effect of various process parameters on the response percentage reduction in surface roughness using response surface methodology (RSM) at 0.16 duty cycle.

Designing the Topology of a Unipolar Pulsed-DC Power Supply using the Open-source Scilab/Xcos Software for a Low-cost Plasma Etcher

We proposed a design topology for a unipolar pulsed direct-current power supply to produce low-cost reactive plasma etcher system. The design was simulated by a block diagram method using the open-source software Scilab/Xcos, and the results were validated by prototyping the power supply. In the topology, the snubber circuit and the RLC circuit play a critical role in producing a smoother pulse waveform and regulating the characteristics of the plasma current. Their optimized parameters can provide well-controllable duty cycles in the voltage output of the power supply. Moreover, the effect of the duty cycles on the performance of the power supply is analyzed. We found that the duty cycle can adjust the transient response of the plasma current as well as the density of the plasma ions. This aspect is useful not only for reducing the arcing effect but also for modifying the surface wettability of the treated substrates. As a result, the glass substrates treated with a 100% duty cycle becomes more hydrophilic, while those treated with a 20% duty cycle tend to be more hydrophobic.

Design and Implementation of DC Pulsed Power Supply Employing Self-Excited Induction Generators and Flywheels for Toroidal Field Coils of a Tokamak Device, PLATO

Tokamak devices with non-superconducting coils must be equipped with pulsed power supplies employing energy storage system when the devices cannot receive electricity from power grids directly. Flywheel energy storage system (FESS) for the coil power supplies have been used only in large or middle-sized tokamak devices since they employed synchronous motor generators (SMGs), which have difficulty in downsizing and maintenance. In our previous research, FESS with induction motor generators (IMGs) utilizing self-excited phenomena was developed. In this paper, using two novel concepts of multiple IMGs and installing a multistage converter, both of design flexibility and coil current ripple reductions are realized. As an experimental result, a peak load power of 778 kW and an electric energy supply of 408 kJ to the dummy coil were achieved using a toroidal field coil power supply (TFCPS) of a tokamak device, PLATO.