78 research outputs found
Introduction to investigations of the negative corona and EHD flow in gaseous two-phase fluids
No full textA simple method of determination of electron density in positive−column He−metal laser discharges
No full textOverview of the Hydrogen Production by Plasma-Driven Solution Electrolysis
No full textThis paper reviews the progress in applying the plasma-driven solution electrolysis (PDSE), which is also referred to as the contact glow-discharge electrolysis (CGDE) or plasma electrolysis, for hydrogen production. The physicochemical processes responsible for the formation of PDSE and effects occurring at the discharge electrode in the cathodic and anodic regimes of the PDSE operation are described. The influence of the PDSE process parameters, especially the discharge polarity, magnitude of the applied voltage, type and concentration of the typical electrolytic solutions (K2CO3, Na2CO3, KOH, NaOH, H2SO4), presence of organic additives (CH3OH, C2H5OH, CH3COOH), temperature of the electrolytic solution, the active length and immersion depth of the discharge electrode into the electrolytic solution, on the energy efficiency (%), energy yield (g(H2)/kWh), and hydrogen production rate (g(H2)/h) is presented and discussed. This analysis showed that in the cathodic regime of PDSE, the hydrogen production rate is 33.3 times higher than that in the anodic regime of PDSE, whereas the Faradaic and energy efficiencies are 11 and 12.5 times greater, respectively, than that in the anodic one. It also revealed the energy yield of hydrogen production in the cathodic regime of PDSE in the methanol–water mixture, as the electrolytic solution is 3.9 times greater compared to that of the alkaline electrolysis, 4.1 times greater compared to the polymer electrolyte membrane electrolysis, 2.8 times greater compared to the solid oxide electrolysis, 1.75 times greater than that obtained in the microwave (2.45 GHz) plasma, and 5.8% greater compared to natural gas steam reforming
Plasma processing methods for hydrogen production
No full textIn the future a transfer from the fossil fuel-based economy to hydrogen-based economy is expected. Therefore the development of systems for efficient H2 production becomes important. The several conventional methods of mass-scale (or central) H2 production (methane, natural gas and higher hydrocarbons reforming, coal gasification reforming) are well developed and their costs of H2 production are acceptable. However, due to the H2 transport and storage problems the small-scale (distributed) technologies for H2 production are demanded. However, these new technologies have to meet the requirement of producing H2 at a production cost of $(1–2)/kg(H2) (or 60 g(H2)/kWh) by 2020 (the U.S. Department of Energy’s target). Recently several plasma methods have been proposed for the small-scale H2 production. The most promising plasmas for this purpose seems to be those generated by gliding, plasmatron and nozzle arcs, and microwave discharges. In this paper plasma methods proposed for H2 production are briefly described and critically evaluated from the view point of H2 production efficiency. The paper is aiming at answering a question if any plasma method for the small-scale H2 production approaches such challenges as the production energy yield of 60 g(H2)/kWh, high production rate, high reliability and low investment cost
Microwave Metamaterial Absorber with Radio Frequency/Direct Current Converter for Electromagnetic Harvesting System
No full textThis article presents the analysis of the electromagnetic (EM) properties of a novel metamaterial (MM) array in the microwave frequency range. The background for this work is the rapid development of portable devices with low individual energy consumption for the so-called “Internet of Things” (IoT) and the demand for energy harvesting from the environment on a micro scale through harvesters capable of powering billions of small receivers globally. The main goal of this work was to check the potential of the novel MM array structure for EM energy harvesting. The proposed MM array was analyzed in the CST Studio simulation environment. This resulted in the determination of the substitute average EM parameters (absorption, reflection, and transmission) of the MM array. Then, the MM array was manufactured, and the simulation results of the MM array parameters were experimentally validated in a microwave waveguide test system. Based on this conclusion, a prototype of the microwave MM absorber, together with an RF/DC converter, was designed and manufactured for harvesting EM energy from the environment. The system’s energy efficiency was evaluated, and its potential application in energy harvesting technology was appraised. Using a microwave horn antenna, the EM energy harvesting efficiency of the prototype was evaluated. It was about 50% at a microwave frequency of about 2.6 GHz. This may make the prototype attractive as an EM energy harvester or bolometric sensor
Temporal and Spatial Development of the EM Field in a Shielding Enclosure with Aperture after Transient Interference Caused by a Subnanosecond High-Energy EM Plane Wave Pulse
No full textA proper assessment of the shielding effectiveness of an enclosure with aperture under subnanosecond transient interference requires a better understanding of the coupling and development mechanisms of the EM field induced inside the enclosure. In this paper, the results of a numerical study of the temporal and spatial development of the electromagnetic (EM) field in a shielding enclosure with aperture after transient interference caused by a subnanosecond high-energy EM plane wave pulse are presented. The interference pulse had Gaussian distribution of the electric and magnetic fields with amplitudes of 106 V/m and 2.68·103 A/m, respectively. The maximum pulse power density was 2.68 GW/m2. The novelty of this study was 2D and 3D images, which visualized the temporal and spatial build-up of electric and magnetic fields in the shielding enclosure within 90 ns after the transient interference. This is 58 times longer than the time needed by any EM wave to travel the distance between the front and rear walls of the enclosure. The presented images, showing the EM field morphology over a relatively long period of time, were crucial for understanding the EM field build-up process inside the shielding enclosure with aperture. They revealed the existence of two unknown phases of the EM field build-up in the enclosure with aperture. We call these two phases the wave phase and the interference phase. In the wave phase, the EM field is generated in the form of so-called primary and secondary wave pulses, traveling towards the enclosure rear wall. In the interference phase, the EM field has the form of temporally and spatially varying pulse-like interference (size-limited) patterns of the associated electric and magnetic fields. The EM field induced in the enclosure is long-lasting compared to the interference pulse duration. The amplitudes of the electric and magnetic fields decreased about threefold in 5 ns and 30-fold in 90 ns, thus exhibiting a severe EM hazard for much longer than the external interference duration. For a long period of time, the highest EM field amplitudes would change their locations in the enclosure, which makes it difficult to assess the shielding effectiveness on the basis of classical definitions. The existence of the long-lasting temporally and spatially varying EM field induced in the enclosure with aperture by the subnanosecond transient interference, visualized in detail in this paper, confirms that a new definition and measurement methods of shielding effectiveness under transient conditions are needed. The obtained results provide a source of data that can be useful when working on the introduction of time-domain parameters to evaluate the transient shielding effectiveness in the case of the ultrashort EM interference
Determination of Shielding Effectiveness of a Subnanosecond High-Power EM Interference by an Enclosure with Aperture Using Time Domain Approach
No full textThe most likely intentional high-power electromagnetic (EM) interference, threatening the operation of technologically advanced electronic infrastructure, will have the forms of sub- and nanosecond ultra-wideband (UWB) pulses, several hundred nanosecond pulses of attenuated sinusoids, and sub- and microsecond sinusoidal pulses. The protection of electronic objects against high-power EM pulses is provided by different types of metal enclosure shields with technological apertures, inside which sensitive electronic objects can be placed. These technological apertures allow external EM interference to penetrate into the enclosure, making the EM shielding imperfect. The EM protection against the EM pulses has been mainly assessed based on the so-called shielding effectiveness (SE) parameters. The SE parameters (SEe and SEm for the electric and magnetic fields, respectively) are useful for designing and comparing EM shields. In relatively small shielding enclosures, which have recently become the subject of interest, the SE parameters have been studied for relatively long transient EM interference, longer than 150 ns, i.e., for the EM pulses whose duration is much longer than the time that the pulse takes to pass the small enclosure. In this work, we dealt with an ultrashort transient interference pulse, the duration of which was much shorter than the pulse transit time through the enclosure. The intentional high-power EM subnanosecond UWB pulse is an example of such a pulse. For such an ultrashort pulse, we studied the EM shielding performance of a small size enclosure numerically (W:H:D = 455 mm:50 mm:463 mm) with aperture (W:H = 80 mm:30 mm). The ultrashort EM interference pulse of a Gaussian distribution of the electric and magnetic fields with amplitudes of 106 V/m and 2.68·103 A/m, respectively, applied in this study, had a duration of 0.0804 ns (FWHM). This means that the high-power EM interference pulse was about 18 times shorter than the time that it takes to pass the enclosure (equal to about 1.5 ns). Our numerical simulations of the subnanosecond high-power EM interference of the interior of the enclosure with aperture were performed in the time domain using the commercial code CST Microwave Studio. First of all, the time-domain simulations resulted in 2D and 3D images and 2D vector maps of the electric and magnetic fields, which visualized the temporal and spatial development of the EM field in the enclosure with aperture caused by the incident subnanosecond high-power EM interference. The development of the associated electric and magnetic fields proceeded in two phases: first in the form of EM waves and later as an interference pattern, traveling forth and back between the front and rear enclosure walls. Due to the energy loss through the aperture, suffered by the traveling EM field and the tendency of the EM field to be evenly distributed over time throughout the entire enclosure, the amplitudes of the EM field decreased about 30 times within 90 ns. Despite the energy loss, the EM field developed in the enclosure existed at least 1000 times longer than the subnanosecond duration of the incident EM pulse (i.e., at least 90 ns as demonstrated by the numerical calculation). Apart from the EM field development visualization, the time-domain simulation enabled easy tracking of the temporal behavior of the EM field in selected points in the enclosure. Such tracking showed that each point in the enclosure was passed by a series of subnanosecond EM pulses, called internal EM pulses, over a relatively long time (at least over the simulation duration of 90 ns). This means that over 90 ns, the points in the enclosure were repeatedly influenced by the series of about 500 subnanosecond internal EM pulses. The amplitudes of many of these pulses were only (3–5) times lower than that of the incident EM pulse. Despite the lower amplitudes, these internal pulses may cause severe EM interference inside the enclosure. This shows a substantial change in the nature of the EM interference caused by a subnanosecond high-power EM plane wave when a given point is not shielded (a single interference of the subnanosecond strong EM pulse) and when a given point is shielded by the enclosure with aperture (a repetitive interference of subnanosecond weaker EM pulses). With the time dependence of the EM field amplitudes obtained from the time-domain calculation at a selected point in the enclosure, it is easy to determine the SEe and SEm at that point as a function of time. In this way, evaluation of the local SEe and SEm (for selected points in the enclosure) can be performed. Moreover, the 2D and 3D images and 2D vector maps calculated in the time domain for a given time enabled easy calculation of the SEe and SEm maps for various times. Such maps, shown for the first time in this paper, give a more global view of the shielding properties of the enclosure with an aperture. This all shows the advantages of the use of the time-domain approach for studying EM shielding in the case of ultrashort EM interferences
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