Corona Charging Research Articles

Bifunctional ZIF-8 Grown Webs for Advanced Filtration of Particulate and Gaseous Matters: Effect of Charging Process on the Electrostatic Capture of Nanoparticles and Sulfur Dioxide.

Metal-organic framework (MOF), an emerging class of porous hybrid inorganic-organic crystals, has been applied for various environmental remediation strategies including liquid and air filtration. In this study, the role of the zeolite imidazole framework-8 (ZIF-8) was explored on the charge trapping ability and its contribution to capturing the targeted pollutants of NaCl nanoparticles and SO2 gas. Poly(lactic acid) fibers with controlled surface pores were electrospun using water vapor-induced phase separation, and the fiber surface was uniformly coated with ZIF-8 crystals via an in situ growth method. As a novel process approach, the corona charging process was applied to the ZIF-8 grown webs. The ZIF-8 promoted the charge trapping in the corona process, and the charged ZIF-8 web showed a significantly improved electrostatic filtration efficiency. Also, the charged ZIF-8 web showed an enhanced SO2 capture ability, both in the static and dynamic air flow states, demonstrating the applicability as a bifunctional filter for both particulate and gaseous matters. The approach of this study is novel in that both particulate and gas capture capabilities were associated with the charge trapping ability of ZIF-8, implementing the corona charging process to the ZIF-8 webs.

Programmable Tactile Feedback Patterns for Cognitive Assistance by Flexible Electret Actuators

AbstractAdvanced tactile feedback systems are important tools in the field of human–machine interfaces. In this work, an airflow‐assisted corona charging process is utilized to charge films made of electret material for the construction of a sandwich‐structured flexible actuator system. With a voltage as low as 20 V, this flexible actuator can stimulate skin sensations for basic tactile feedback functions. Under a driving voltage of 200 V, the system can generate an output force of ≈55 mN, which is larger than that of the output force by cellphones under the vibration mode. Utilizing these prototype flexible electret actuators array, programmable patterns of tactile sensations can be generated on human skin according to both vibrational intensities and spatial positions. Thus, two demonstrations of human–machine interface are illustrated based on the proposed device: 1) A tactile‐assisted navigation prototype with programmable commands; and 2) a tactile‐based braille prototype constructed via a 6‐pixels actuator array to generate designated patterns for assisting human–machine communications. As such, this system prototype has potential for applications in cognitive assistance via tactile feedbacks.

Ultrathin Stretchable Triboelectric Nanogenerators Improved by Postcharging Electrode Material.

Sustainable ultrathin stretchable power sources have emerged with the development of wearable electronics. They obtain energy from living organisms and the environment to drive these wearable electronics. Here, an ultrathin stretchable and triboelectric nanogenerator (TENG) improved by chargeable carbon black (CB)/thermoplastic polyurethane (TPU) composite material (CT-TENG) is proposed for mechanical energy harvesting and physiological signal sensing. The CB/TPU composite can act as both a stretchable electrode and a triboelectric layer due to the coexistence of conductive CB and dielectric TPU. The CT-TENG demonstrates good stretchability (≈646%), ultrathin thickness (≈50 μm), and a lightweight (≈62 mg). The triboelectric electrode material can be improved by postcharging treatment. With the corona charging process, the output performance of the CT-TENG was improved eightfold and reached 41 V. Moreover, the CT-TENG with a self-powered sensing capability can inspect the amplitude and frequency of different physiological movements. Consequently, the CT-TENG is promising in promoting the development of electronic skins, wearable systems of self-powered sensors, human-machine interactions, soft robotics, and artificial intelligence applications.

The Problem of Control Actions on the Lightning Discharge

The specificity of the development of a counter discharge from a grounded electrode in the field of a negative stepped lightning leader has been established. It is shown that high-voltage control pulses are effective only when acting directly on a counter leader. Analytical expressions are derived for estimating the conditions for the start of the counter discharge directly in the streamer form, which bypasses the stage of nonstationary ultra corona, and also for determining the amplitude of the control pulse capable of exciting an upward lightning from an electrode of a given height in the atmosphere free from the ultra corona charge. The parameters of the control voltage pulse for the excitation of a trigger lightning in a real thunderstorm situation are determined by numerical simulation. A sharp decrease in the effectiveness of control actions with the duration of a few microseconds is established. It is experimentally proven that the consequences of the impact of such pulses is a delay in the formation of a counter leader, but not in any way its stimulation. The origin of the decrease in the efficiency of lightning rods of early streamer initiation in comparison with traditional ones of the same height is established.

Unravelling the silicon-silicon dioxide interface under different operating conditions

Silicon dioxide (SiO2) has played a critical role in the development of high-efficiency silicon (Si)-based photovoltaic devices. Recently, it has experienced a renaissance as an interlayer in many of the new contact passivating structures. Studies have extensively investigated the recombination process at the Si–SiO2 interface, however, only little is known about the impact of temperature on the surface recombination. In this study, we investigate the recombination at the Si–SiO2 interface by varying the temperature, excess carrier density, and dielectric fixed charge. An improved lifetime is observed with increasing temperature. A forming gas anneal is used to improve the passivation quality, however, at higher temperatures, the hydrogenated interface passivation degrades due to increased surface state density. The degradation is stronger for corona-charged SiO2, due to the instability of the corona charge within the dielectric. Using the extended Shockley-Read Hall recombination model, the Si–SiO2 interface defects’ parameters are extracted. Most importantly, we determine the value and the temperature-dependence of the capture cross-sections at this interface.

Drift-diffusion model of corona discharge in coaxial geometry due to negative lightning impulse voltage

Corona discharge at atmospheric pressure in cylindrical geometry is simulated numerically for negative lightning voltage impulse. The simulation is performed by solving the drift-diffusion-reaction equations for electrons, positive and negative ions. Spatial dependence and time evolution of the concentration of charged particles and created space electric field are used for detailed theoretical analysis of corona discharge based on the values of the transport and reaction gaseous coefficients. This exact drift-diffusion model enables clear physical picture of the corona discharge dynamics. It is used for the determination of the charge-voltage curves necessary for taking into account the corona effects in transient overvoltage calculation on transmission lines. In contrary to the previous engineering corona models, it is shown that the corona charge continues to increase although the input voltage pulse decreases after reaching its maximum value. This behavior is confirmed by measurements in a few experimental studies. Secondly, it has been shown that according to this model there are no positive streamers formation departing from central electrode or wire during decreasing edge of the input voltage pulse. The total charge simply commences to decrease when the negative ions neutralize themselves on the central electrode or wire of positive polarity. A sharp peak of corona current is observed immediately after the beginning of the intense ionization. The drift-diffusion model could also be used to check the validity of other common assumptions and predictions of previous engineering corona models.

Multi-Layered, Corona Charged Melt Blown Nonwovens as High Performance PM0.3 Air Filters.

Particulate matter (PM) and airborne viruses bring adverse influence on human health. As the most feasible way to prevent inhalation of these pollutants, face masks with excellent filtration efficiency and low press drop are in urgent demand. In this study, we report a novel methodology for producing high performance air filter by combining melt blown technique with corona charging treatment. Changing the crystal structure of polypropylene by adding magnesium stearate can avoid charge escape and ensure the stability of filtration performances. Particularly, the influence of fiber diameter, pore size, porosity, and charge storage on the filtration performances of the filter are thoroughly investigated. The filtration performances of the materials, including the loading test performance are also studied. The melt blown materials formed by four layers presented a significant filtration efficiency of 97.96%, a low pressure drop of 84.28 Pa, and a high quality factor (QF) of 0.046 Pa−1 for paraffin oil aerosol particles. Meanwhile, a robust filtration efficiency of 99.03%, a low pressure drop of 82.32 Pa, and an excellent QF of 0.056 Pa−1 for NaCl aerosol particles could be easily achieved. The multi-layered melt blown filtration material developed here would be potentially applied in the field of protective masks.

Polymer, Additives, and Processing Effects on N95 Filter Performance.

The current severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) pandemic has highlighted the need for personal protective equipment, specifically filtering facepiece respirators like N95 masks. While it is common knowledge that polypropylene (PP) is the industry standard material for filtration media, trial and error is often required to identify suitable commercial precursors for filtration media production. This work aims to identify differences between several commercial grades of PP and demonstrate the development of N95 filtration media with the intent that the industry partners can pivot and help address N95 shortages. Three commercial grades of high melt flow index PP were melt blown at Oak Ridge National Laboratory and broadly characterized by several methods including differential scanning calorimetry (DSC), X-ray diffraction (XRD), and neutron scattering. Despite the apparent similarities (high melt flow and isotacticity) between PP feedstocks, the application of corona charging and charge enhancing additives improve each material to widely varying degrees. From the analysis performed here, the most differentiating factor appears to be related to crystallization of the polymer and the resulting electret formation. Materials with higher crystallization onset temperatures, slower crystallization rates, and larger number of crystallites form a stronger electret and are more effective at filtration.

Charging of Piezoelectric Cellular Polypropylene Film by Means of a Series Dielectric Layer.

Piezoelectric polymer cellular films have been developed and improved in the past decades. These piezoelectric materials are based on the polarization of the internal cells by means of induced discharges in the gas inside the cells. Internal discharges are driven by an external applied electric field. With this polarization method, cellular polypropylene (PP) polymers exhibit a high piezoelectric coefficient d33 and have been investigated because of their low dielectric polarization, high resistivity, and flexibility. Charging polymers foams is normally obtained by applying a corona discharge to the surface with a single tip electrode-plane arrangement or a triode electrode, which consists of a tip electrode-plane structure with a controlled potential intermediate mesh. Corona charging allows the surface potential of the sample to rise without breakdown or surface flashover. A charging method has been developed without corona discharge, and this has provided good results. In our work, a method has been developed to polarize polypropylene foams by applying an insulated high-voltage electrode on the surface of the sample. The dielectric layer in series with the sample allows for a high internal electric field to be reached in the sample but avoids dielectric breakdown of the sample. The distribution of the electric field between the sample and the dielectric barrier has been calculated. Experimental results with three different electrodes present good outcome in agreement with the calculations. High d33 constants of about 880 pC/N have been obtained. Mapping of the d33 constant on the surface has also been carried out showing good homogeneity on the area under the electrode.

Traps energy distribution in Kapton HN polyimide films through surface potential decay model under humidity conditions

In this paper, an experimental study and analysis of the effects of environmental relative humidity (RH %) on the transport mechanisms of electrical charges in 50 μm thick Kapton HN polyimide (PI) films have been presented. The evolution of the surface potential decay with time after negative corona charge deposition have been investigated and analyzed by examining the tdV/dt characteristics to straightly obtain information about trap energy distribution in PI films for different relative humidity levels (35, 50, 70 and 90%). The calculating method of trap energy distribution is based on the double exponential fitting analysis of surface potential decay measurements. Two peaks were observed in the trap charge density distribution curve with trap levels, which is agreed with the presence of the shallow and deep traps. The results indicate that for different charging voltage levels, the surface potential decays faster in humid air (RH = 90%) than in relatively dry ones (RH = 35%). The recorded corona charging current confirms the interpretation of surface potential decay measurements. In addition, the density and depths of both shallow and deep traps change with charging voltage and relative humidity levels. Both shallow and deep trap distribution moves towards lower energy levels, indicating an increase in the film's electrical conductivity.

Electron-ion Technology Modular Fine Gas Cleaning Apparatus

For the process gases cleaning from dust in sinter production, different types and designs of apparatus are used. These are battery multicyclones and electrocyclones, bag filters, as well as electrostatic precipitators of various designs. However, only electrostatic precipitators have clear advantages. The purpose of this article is to improve the design of an electrostatic precipitator by increasing the efficiency of collecting dust, using electronic-ion technology with the combined movement of dusty gases and reducing the size. The improvement is based on the task of introducing a new architecture for constructing an electrostatic precipitator. The use of this improvement will contribute to the creation of lighter and more compact electrostatic precipitators, will make it possible to regulate the resistance of the apparatus, which affects the efficiency, depending on the dust load and the dispersion composition of the solid component. Computer modeling was carried out in order to establish the mechanism of the aerodynamic forces influence of the gas flow and to determine the dependence of the drift velocity and the direction of movement of charged dispersed particles on the velocity of the medium being purified during the combined course of gases in the electrostatic precipitator. The problem is solved by the fact that the electrostatic precipitator has a modular structure and consists of a voltage unit, a charging unit with a system of crown needle electrodes made in the form of needle plates 0.2... 0.5 m long and 0.020... 0.030 m wide, connected to the deposition unit, in which the deposition electrodes are installed perpendicular to the gas flow with the possibility of regulation and fixation at any angle to the direction of movement of the gas flow. The technical result is an increase in the density of the corona charge, the efficiency of the deposition process, a decrease in the overall dimensions of the electrostatic precipitator, and a decrease in the time of its manufacture, adjustment and installation. A gas cleaning apparatus of modular type “MV-2” has been developed, in which a new modular layout and technology of gas cleaning are applied. The device makes it possible to provide the required emission standards in a much smaller size in the range of 20... 50 mg/m³, depending on the parameters of the dust and gas flow entering for cleaning and the fractional composition of dust.

Studying properties of corona electret based on compositions of polylactic acid and bentonite

The study focuses on the composites of polylactic acid and bentonite as well as corona electrets based on them. The paper explores rheological, electrical, physical and mechanical properties of the composites as well as the effect of corona charging on their properties. Differential scanning calorimetry was used to assess transition temperatures in the compositions. Surface potential, electric field strength and effective surface charge density were measured. Optimal performance was shown by the compositions of polylactic acid with 4% bentonite.

The Effect of Temperature and Humidity on the Filtration Performance of Electret Melt-Blown Nonwovens.

Electret melt-blown nonwovens are widely used for air purification due to their low pressure drop and high filtration efficiency. However, the charge stability could be affected by the ambient temperature and humidity, reducing the filtration efficiency, resulting in the electret melt blown filter not providing effective protection. Herein, we used corona charge to prepare electret melt-blown nonwovens and systematically studied the effects of different temperature and humidity on the structure, morphology, filtration performance, and surface potential within 24 h. The effect of treatment temperature and humidity on pressure drop was minimal because the fiber morphology and web structure of melt-blown nonwovens were not damaged. When the treatment temperature was lower than 70 °C, the effect on the filtration efficiency of the sample was small, but when the temperature increased to 90 or 110 °C, the filtration efficiency decreased significantly with the increase of the treatment time, and the surface potential also declined similarly. In conclusion, high temperatures will lead to charge escape and reduce the electrostatic adsorption effect. Furthermore, at the same temperature, increasing relative humidity can accelerate the charge release and make the filtration efficiency drop more. After the sample was treated at 110 °C and 90% relative humidity for 24 h, the filtration efficiency decreased from 95.49% to 38.16% at a flow rate of 14.16 cm s−1, and the surface potential dropped to the lowest value of −1.01 kV. This result shows that all links of electret melt-blown filter material from raw material to final use should be avoided in high temperature and high humidity conditions to ensure the protection effect.

Probing local charge distribution of an electret — A case study with a PVDF polymer

A simple versatile way of producing mini electret pieces with a handheld corona charging device is reported here. Its adaptability and suitability are demonstrated using a PVDF polymer. A quantitative assessment of the electret pieces is made by probing local charge distribution using electric force microscopy. The results are expected to be useful for polymer-based applications like dust filters that protect in the sub-micron range and for possible drug release devices.

Leader Charges, Currents, Ambient Electric Fields, and Space Charges Along Downward Positive Leader Paths Retrieved From Ground Measurements in Metropolis

AbstractAn approach for retrieving the leader channel charge density, leader current, ambient electric field, and space charge along a leader channel path from ground observations with a complicated ground condition was presented. With this approach, properties of two downward positive leaders (DPL1 and DPL2) struck at high‐rise buildings were studied based on electric and optical measurements made on the roof of a 100 m high building in Guangzhou, China. It shows that the leader‐produced electric field on the roof of the 100 m high building was about 4 times of that on flat ground. The 2‐D speed for both leaders showed a general increasing trend as the leader going down, in the range of 1.8 to 32.3 × 105 and 1.7 to 46.9 × 105 m/s, respectively. The channel line charge density for both leaders showed firstly a sharp increasing trend and then a decreasing trend as the leader going down, in the range of 0.4 to 8.6 and 0.4 to 15.2 mC/m, respectively. The current of the two leaders varied in the range of 0.7 to 5.4 and 0.7 to 4.6 kA, respectively. The ambient electric field (downward is positive) for both leaders showed an alternating polarity along the leader path, in the range of −120 to +176 and −250 to +180 kV/m, respectively. The space charge for both leaders showed also an alternating polarity along the leader path, in the range of −12.3 to +4.2 and −13.9 to +7.8 nC/m3, respectively, which may reflect the in‐cloud electric structure and the corona charge distribution between the cloud and ground.

Observations of corona point discharges from grounded rods under thunderstorms

We investigated features of corona point discharges when a grounded conductive rod is subject to a high background electric field. In the laboratory, high voltage is applied to an upper plate in a plane-to-point experiment, and the discharges are observed from a grounded rod using an ultraviolet camera and a photosensor. The current is measured using a shunt resistor, a current transformer, and a high impedance ammeter. We have found that corona current pulses have fast rise time (tens of nanoseconds) and slow decay (hundreds of nanoseconds). For the initial stage of the discharges, above a certain threshold, the frequency of pulses increases with the voltage applied. In the field, one current sensor coupled to a grounded rod, 1.5 m above a roof, was installed in a site located at an altitude of 2525 m above sea level. The same pulses observed in the laboratory are recorded during periods of electric field enhancement caused by the movement of charged clouds or lightning activity near the sensor. For that specific installation, the frequency of pulses is correlated with the ambient electric field measured 250 m away. To the best knowledge of the authors, this is the first time in which such correlation is made for outdoor measurements, seeing that other works correlate the electric field with the average current flow. Pulses of positive corona were no longer observed when the electric field magnitude was lower than 1.8 kV/m and pulses of negative corona were more atypical and presented a higher threshold, of about 3.8 kV/m. This study is relevant for understanding the production of corona and space charges in high structures, such as wind turbine blades, towers, and buildings in general.

Effect of Aging under AC Superimposed Harmonic Voltage on Trap and Carrier Transport Properties of Silicone Rubber

The rapid growth of power grid capacity and the widespread use of a large number of power electronics and non-linear loads have led to harmonics in the power system. Harmonics in the power system will cause safety hazards to the normal operation of power equipment, exacerbate the aging of insulation materials, and reducing the overall operation reliability of the system. In the present work, we used power frequency ac voltage superimposed harmonics to carry out ageing experiments on power cable terminals. Then, we tested the infrared spectra, dielectric spectra, electrical conductivity, and surface potential decay characteristics of silicone rubber insulation materials on the cable terminals aged for different times. The experimental results show that the dielectric constant and dielectric loss of silicone rubber gradually increase with the aging time. In particular, the dielectric loss of silicone rubber changed greatly at low frequencies. The effect of dc conductance of aged silicone rubber on dielectric loss is significantly enhanced at low frequencies, which causes the dielectric loss to increase as the frequency decreases following an inverse power law. The surface potential decay rates of silicone rubber insulation after positive and negative corona charging accelerate with increasing the aging time, which is consistent with the experimental results of electrical conductivity. By analyzing the distribution characteristics of electron and hole traps in silicone rubbers, it is found that the trap energy levels of electron and hole traps become shallower as the operating time increases. The calculation of the carrier hopping conduction model shows that the shallow trap formed with increasing the aging time will lead to increases in both carrier mobility and conductivity. When the conductivity rises to a certain value, the silicone rubber will lose its insulation performance, resulting in insulation failure.

An Innovation in Corona Charging of Electrets

An innovation in corona charging of electrets of polymer films has been adopted in locally designed and fabricated corona charging set up by replacing the regular high voltage DC power supply with a light, portable handy 3V-6V DC to DC 400kV boost step-up power module high voltage generator. Polymer film electrets of polyethylene transparency film have been corona charged using this innovative setup. The measurements were done and the results have been analyzed in the light of cited literature to show the effectiveness and advantage of the innovation.

Rapid Airborne Influenza Virus Quantification Using an Antibody-Based Electrochemical Paper Sensor and Electrostatic Particle Concentrator.

Airborne influenza viruses are responsible for serious respiratory diseases, and most detection methods for airborne viruses are based on extraction of nucleic acids. Herein, vertical-flow-assay-based electrochemical paper immunosensors were fabricated to rapidly quantify the influenza H1N1 viruses in air after sampling with a portable electrostatic particle concentrator (EPC). The effects of antibodies, anti-influenza nucleoprotein antibodies (NP-Abs) and anti-influenza hemagglutinin antibodies (HA-Abs), on the paper sensors as well as nonpulsed high electrostatic fields with and without corona charging on the virus measurement were investigated. The antigenicity losses of the surface (HA) proteins were caused by H2O2 via lipid oxidation-derived radicals and 1O2 via direct protein peroxidation upon exposure of a high electrostatic field. However, minimal losses in antigenicity of NP of the influenza viruses were observed, and the concentration of the H1N1 viruses was more than 160 times higher in the EPC than the BioSampler upon using NP-Ab based paper sensors after 60 min collection. This NP-Ab-based paper sensors with the EPC provided measurements comparable to quantitative polymerase chain reaction (qPCR) but much quicker, specific to the influenza H1N1 viruses in the presence of other airborne microorganisms and beads, and more cost-effective than enzyme-linked immunosorbent assay and qPCR.

Experimental Evaluation of Bipolar Surface Potential with Corona Charging for Electret Activation

Experimental Evaluation of Bipolar Surface Potential with Corona Charging for Electret Activation