Table of contents

Electrostatics 2011 was held in the city of Bangor which is located in North West Wales in an area of outstanding natural beauty close to the Snowdonia mountain range and bordering the Irish Sea. The history of the area goes back into the mists of times, but a continuous technological thread can be traced from the stone- and bronze-age craftsmen, who inhabited the area several thousand years ago, via the civil engineering and fortifications of the Romans and Edward I of England, through Marconi's long-wave trans-Atlantic transmitter near Caernarfon to the conference host. The School of Electronic Engineering at Bangor University has contributed much to the discipline of Electrostatics not only in teaching and research but also in supporting industry. It was a great pleasure for me, therefore, to have the pleasure of welcoming the world's experts in Electrostatics to Bangor in April 2011.

In my preface to the Proceedings of Electrostatics 1999, I reported that almost 90 papers were presented. Interestingly, a similar number were presented in 2011 testifying to the importance and endurance of the subject. The all-embracing nature of electrostatics is captured in the pictorial depiction used for the conference logo: a hand-held plasma ball with its close link to gaseous discharges and the superimposed Antarctic aurora highlighting the featured conference themes of atmospheric, planetary and environmental electrostatics. Leading these themes were three invited contributions, the first by Giles Harrison who delivered the Bill Bright Memorial Lecture 'Fair weather atmospheric electricity', Carlos Calle on 'The electrostatic environments of Mars and the Moon' and Istvan Berta on 'Lightning protection – challenges, solutions and questionable steps in the 21st century'. Leading other key sessions were invited papers by Atsushi Ohsawa on 'Statistical analysis of fires and explosions attributed to static electricity over the last 50 years in Japanese industry' and Antonio Ramos on 'Electrohydrodynamic pumping in microsystems'.

Of the papers submitted for publication 69 passed through the thorough review process and I take this opportunity to warmly thank the reviewers for their constructive criticism and rapid turnaround which has allowed the Proceedings to be delivered to the publisher on time. It is a pleasure also to thank members of the International Advisory Panel, and the Organizing and Programme Committees for their guidance and suggestions and especially Claire Garland and her team at the Institute of Physics for their support, all of which ensured a successful and enjoyable conference. Special thanks are due to Jeremy Smallwood for organising the pre-conference workshop, to Tom Jones, Martin Glor and Dave Swenson for their highly informative and educational contributions at the workshop, to CST for organising the simulation workshop, and to CST and JCI Chilworth for their much appreciated sponsorship of the conference.

I am sure you will enjoy reading this record of Electrostatics 2011, covering as it does the wide range of subjects upon which static electricity impinges. Especially important is the development of electrostatic-based methods for reducing atmospheric pollution. In this context it is interesting to see how Masuda's work on the surface-discharge-based Boxer charger, first reported over 30 years ago, has now developed into dielectric barrier discharge (DBD) systems for the removal of noxious molecules from industrial and vehicle exhaust gases.

Thanks to our hard working conference chairman, Paul Holdstock, the conference retained its now well-established reputation for providing a friendly, sociable atmosphere for discussing the newest developments in this important scientific area. Finally, my sincere thanks go to all the presenters and to all those who attended and contributed to another successful conference.

Professor D. Martin Taylor

Proceedings Editor

Bangor, May 2011

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Not long after Franklin's iconic studies, an atmospheric electric field was discovered in "fair weather" regions, well away from thunderstorms. The origin of the fair weather field was sought by Lord Kelvin, through development of electrostatic instrumentation and early data logging techniques, but was ultimately explained through the global circuit model of C.T.R. Wilson. In Wilson's model, charge exchanged by disturbed weather electrifies the ionosphere, and returns via a small vertical current density in fair weather regions. New insights into the relevance of fair weather atmospheric electricity to terrestrial and planetary atmospheres are now emerging. For example, there is a possible role of the global circuit current density in atmospheric processes, such as cloud formation. Beyond natural atmospheric processes, a novel practical application is the use of early atmospheric electrostatic investigations to provide quantitative information on past urban air pollution.

Atmospheric ionisation from natural radioactivity and cosmic rays has been measured at several sites in Snowdonia from 2005-present. The motivation for this project was a combination of public engagement with science, and research into the effects of ionisation on climate. A four-component atmospheric radiometer instrument is co-located with the ionisation detectors and the data is remotely logged and displayed on the Web. Atmospheric ionisation from natural radioactivity varies with local geology, and the cosmic ray ionisation component is modulated by solar activity and altitude. Variations due to all these effects have been identified and are described.

The electrification of stratiform clouds has is little investigated in comparison with thunderstorms and fair weather atmospheric electricity. Theory indicates that, at the upper and lower horizontal boundaries of layer clouds, charging will arise from vertical flow of cosmogenic ions in the global atmospheric electric circuit. Charge is transferred to droplets and particles, affecting cloud microphysical processes such as collision and droplet activation. Due to the lack of in-situ measurements, the magnitude and distribution of charge in stratiform clouds is not well known. A sensitive, inexpensive, balloon borne charge sensor has been developed to make in-situ measurements of edge charging in stratiform cloud using a standard meteorological radiosonde system. The charge sensor has now been flown through over 20 stratiform clouds and frequently detected charge up to 200 pC m⁻³ near cloud edges. These results are compared with measurements from the same sensor used to investigate charge in particle layers, such as volcanic ash from the Eyjafjallajökull eruption, and Saharan dust in the Cape Verde Isles.

Electrostatic phenomena have long been associated with the explosive eruption of volcanoes. Lightning generated in volcanic plumes is a spectacular atmospheric electrical event that requires development of large potential gradients over distances of up to kilometres. This process begins as hydrated liquid rock (magma) ascends towards Earth's surface. Pressure reduction causes water supersaturation in the magma and the development of bubbles of supercritical water, where deeper than c. 1000 m, and water vapour at shallower depths that drives flow expansion. The generation of high strain rates in the expanding bubbly magma can cause it to fracture in a brittle manner, as deformation relaxation timescales are exceeded. The brittle fracture provides the initial charge separation mechanism, known as fractoemission [1]. The resulting mixture of charged silicate particles and ions evolves over time, generating macro-scale potential gradients in the atmosphere and driving processes such as particle aggregation. For the silicate particles, aggregation driven by electrostatic effects is most significant for particles smaller than c. 100 μm. Aggregation acts to change the effective aerodynamic behaviour of silicate particles [2], thus altering the sedimentation rates of particles from volcanic plumes from the atmosphere. The presence of liquid phases also promotes aggregation processes [3] and lightning.

A fixed site monitoring station recorded the potential gradient disturbances near to two high voltage power lines during 2008. The full year's results show that the electrical environment downwind of power lines is modified compared to that upwind. Potential gradient disturbance was greater on days when there was rainfall. Humidity was inversely correlated with mean potential gradient when the station was both downwind and upwind of both power lines. Wind speed is weakly correlated with the standard deviation of a 10 minute sample of potential gradient downwind of both power lines, but not upwind. The distributions of mean and standard deviation of potential gradient in 10 minute samples showed that the field was more negative overnight and on days where there was rain, but less variable at night and on dry days. Upwind of the power lines, the average 24 hour trace exhibits the natural background Carnegie curve, with peaks corresponding to increased global thunderstorm activity, while local effects mask this trace when the FSMS is downwind of the power lines. The results show that corona ions can cause potential gradient disturbances downwind of high voltage power lines, most particularly during rain and high humidity, and overnight.

The electrical activity present in the environment near the surfaces of Mars and the moon has very different origins and presents a challenge to manned and robotic planetary exploration missions. Mars is covered with a layer of dust that has been redistributed throughout the entire planet by global dust storms. Dust, levitated by these storms as well as by the frequent dust devils, is expected to be electrostatically charged due to the multiple grain collisions in the dust-laden atmosphere. Dust covering the surface of the moon is expected to be electrostatically charged due to the solar wind, cosmic rays, and the solar radiation itself through the photoelectric effect. Electrostatically charged dust has a large tendency to adhere to surfaces. NASA's Mars exploration rovers have shown that atmospheric dust falling on solar panels can decrease their efficiency to the point of rendering the rover unusable. And as the Apollo missions to the moon showed, lunar dust adhesion can hinder manned and unmanned lunar exploration activities. Taking advantage of the electrical activity on both planetary system bodies, dust removal technologies are now being developed that use electrostatic and dielectrophoretic forces to produce controlled dust motion. This paper presents a short review of the theoretical and semiempirical models that have been developed for the lunar and Martian electrical environments.

Lightning is expected to occur on Mars within dust devils and dust storms, which are likely to discharge in the low pressure carbon dioxide environment. Despite this, radio emissions from Martian lightning have not yet been conclusively observed by remote sensing, nor have there been any in situ measurements of Martian atmospheric electricity. We report laboratory experiments to simulate Martian electrical discharges and measure the radio emissions from them, to facilitate searches of Martian lightning from spacecraft data. Voltage transients were observed in a tank in which Martian analogue simulant was allowed to become triboelectrically charged, and then fall to a sensing electrode. A plausible explanation for our results is that electrical discharges have taken place, caused by charge separation on differently sized particles as predicted by theory. Unlike in previous reports, we have been able to detect discharges without adding glass microballoons to the Martian analogue dust to facilitate the charging, although the addition of glass microballoons did enhance the transient rate.

Asteroid surface material is expected to become photoelectrically charged, and is likely to be transported through electrostatic levitation. Understanding any movement of the surface material is relevant to proposed space missions to return samples to Earth for detailed isotopic analysis. Motivated by preparations for the Marco Polo sample return mission, we present electrostatic modelling for a real asteroid, Itokawa, for which detailed shape information is available, and verify that charging effects are likely to be significant at the terminator and at the edges of shadow regions for the Marco Polo baseline asteroid, 1999JU3. We also describe the Asteroid Charge Experiment electric field instrumentation intended for Marco Polo. Finally, we find that the differing asteroid and spacecraft potentials on landing could perturb sample collection for the short landing time of 20min that is currently planned.

Laboratory tests have shown that the chemical composition of fly ash (in that unburned coal) as well as its size distribution has significant influence on the dust cleaning process. Likewise the design of discharge electrodes has shown a strong influence on the dust cleaning. Tests of precipitation efficiency were carried out on a laboratory electrostatic precipitator (ESP) model using fly ash samples of diverse size distribution and unburned coal content collected from several grate boilers. Test results show explicit dependency of the ESP precipitation efficiency on physical and chemical characteristics of the fly ash, design of discharge electrodes and amount of electrical energy delivered to the ESP. Mercury concentration measurements show higher levels in the fly ash than in the fired coal indicating high sorption capacity of the fly ash. Prior observation suggests good mercury adsorption on fine fly ash particles in the presence of elemental coal. Hence the improvement of ESP collection efficiency of fine particles containing unburned coal may help decrease the emission of mercury.

Pulsed electrical field (PEF) treatment is a non-thermal food preservation technology based on the use of the electrical field in impulses applied in order to inactivate and control pathogen microorganisms in foods. This technology is highly appreciated for its ability to prolong the shelf life of the treated product without the use of heat and also for its ability to preserve the product's sensory qualities and nutritional value as well as for the microbiological control of the treated products. This paper presents the PEF and UV treatment methods, or a combination between the two, for microbe inactivation in liquid products. The experiments were carried out using yeasts, lactic bacteria and acetic bacteria in the following systems: stand-alone treatments (PEF or UV) or in combination (UV+PEF or PEF+UV). The results of these experiments showed that one can obtain total inactivation of microorganisms using the combined UV+PEF system, thus leading to the possibility of increasing liquid food products quality as compared to the quality obtained using thermal pasteurization.

In this paper, a wet type plasma reactor based on a three electrode device is investigated experimentally in order to remove NO and NOx at low flow rate. First, a comparison of cleaning performances of gas exhaust has been performed when the surface discharge operates in DBD or SD modes. From these previous results, the second part of study has consisted to improve the electrochemical conversion of the wet type plasma reactor by adding a coil between the AC HV power supply and the surface discharge. The parametric study has been performed with 100 ppm of NO content in gas flow at room temperature and atmospheric pressure for a flow rate of 1 L/min. For each electrical parameter tested, an electric characterization and measurement of NOx content via FT-IR has been conducted. The results highlight a better cleaning of gas exhaust when the surface discharge operates in DBD mode. Moreover, the presence of solution promotes the arc transition when the operating mode is SD, resulting a reliability reduction of plasma device. In addition, the measurements show that the insertion of coil in the electrical circuit improves the NOx removal at a given power consumption for the DBD operating mode.

The aim of the present work is to investigate the capability of a Wire-to-Square Tube Electrostatic Precipitator (or WST-ESP) to collect submicron particles using a Dielectric Barrier Discharge (DBD). A parametric study is carried out to evaluate the effects of four control variables that might affect the collection efficiency of the WST-ESP: diameter of the corona wire electrode, width of the ground electrode and the area of the tube section. The experimental data show that the wire diameter has a negligible effect on the WST-ESP collection characteristics. However, better overall performances can be obtained by putting in parallel several WST-ESPs with reduced section. The extension of the ground electrode and its discretization increase the collection efficiency.

The filtration of nanoparticles and submicron particles is an important problem in industry and health protection. One of the methods which can be used to solve this problem is to use nonwoven nanofibrous filters. The process of producing filtration mats of different thickness by electrospinning is presented in the paper. The experimental results on filtration properties of nanofibrous filter mat, including the efficiency of removal of cigarette smoke particles from a gas are also presented.

Human illnesses and deaths caused by foodborne pathogens (e.g., Salmonella enterica, Listeria monocytogenes, Escherichia coli O157:H7, etc.) are of increasing concern globally in maintaining safe food supplies. At various stages of the food production, processing and supply chain antimicrobial agents are required to sanitize contact surfaces. Additionally, during outbreaks of contagious pathogenic microorganisms (e.g., H1N1 influenza), public health requires timely decontamination of extensive surfaces within public schools, mass transit systems, etc. Prior publications verify effectiveness of air-assisted, induction-charged (AAIC) electrostatic spraying of various chemical and biological agents to protect on-farm production of food crops...typically doubling droplet deposition efficiency with concomitant increases in biological control efficacy. Within a biosafety facility this present work evaluated the AAIC electrostatic-spraying process for application of antimicrobial liquids onto various pathogen-inoculated food processing and handling surfaces as a food safety intervention strategy. Fluoroanalysis of AAIC electrostatic sprays (−7.2 mC/kg charge-to-mass ratio) showed significantly greater (p<0.05) mass of tracer active ingredient (A.I.) deposited onto target surfaces at various orientations as compared both to a similar uncharged spray nozzle (0 mC/kg) and to a conventional hydraulic-atomizing nozzle. Per unit mass of A.I. dispensed toward targets, for example, A.I. mass deposited by AAIC electrostatic sprays onto difficult to coat backsides was 6.1-times greater than for similar uncharged sprays and 29.0-times greater than for conventional hydraulic-nozzle sprays. Even at the 56% reduction in peracetic acid sanitizer A.I. dispensed by AAIC electrostatic spray applications, they achieved equal or greater CFU population reductions of Salmonella on most target orientations and materials as compared to uncharged sprays and conventional full-rate hydraulic-nozzle sprays.

Giant unilamellar vesicles (GUVs) [1], typically >10 μm in diameter, can serve as interesting models for mimicking biological membranes and furthermore can be usefully leveraged in drug delivery and bio-sensor applications. In this paper, we have demonstrated a chip based vesicle dispensing scheme that utilizes liquid dielectrophoresis (L-DEP) to dispense, precisely positioned GUVs over a range of diameter 30 – 100 μm, a capability that is not readily achieved by either conventional or microchannel technology. These GUVs can also be individually addressed and tailored for a variety of applications such as bio-sensing and cell-on-a-chip.

The aims of this work are to show the influence of adding a series resistance at the output of a discharge generator circuit and to point out that this component can be used to control the spark energy in electrostatic perforation systems. Analysis of the experimental results reveals that there exists a close connection between the resistor value and the obtained perforation pattern both in hole density and size. The use of a series resistor has a strong influence on the material porosity, which is an important industrial parameter for assessing the pattern perforation quality.

This paper is aimed at investigating the characteristics of a sliding discharge (SD) including the onset voltage (V_o), spark voltage (V_S), and current-voltage (I-V) relationship in a multi-rod reactor stressed by sinusoidal AC or pulse voltage. The effects of various parameters (the voltage amplitude, frequency, gas flow rate, and voltage type) on the characteristics of the reactor sliding discharge (V_o, V_S and I-V relationship) have been studied experimentally. It has been found that the DC onset and spark voltages increase with the increase of the gas flow rate, while the effect of the frequency on them is not pronounced. The onset and spark voltages of the stressed reactor for sinusoidal AC voltage are lower than those obtained under a pulse voltage of the same peak value. Subsequently, the sliding current increases with the increase of the sinusoidal AC high voltage, the frequency, and the negative DC voltage, while, it decreases with the increase of the flow rate. It is observed that stressing the reactor with sinusoidal AC voltage gives higher values of sliding current than those obtained using a pulse at the same peak voltage. Stressing the reactor with sinusoidal AC voltage gives higher values of the NO removal efficiency than those obtained using pulse voltage.

In this paper we compare the performance of DBD actuators when either a smooth or saw-like electrode is employed. Two electrode arrangements of DBD actuators are investigated. The first is the classic DBD actuator and the second is a DBD actuator with floating electrode. The usefulness of the saw-like electrode in these two types of DBD actuators is studied.

The new design of plasma reactor with back discharge electrode is presented and characterized. The laboratory scale plasma reactor was constructed in a plane parallel geometry with a gas permeable low-field electrode system. The low-field electrode was covered with a dielectric layer enabling the appearance of back corona discharges. The total volume of the reactor is equal to 2 dm³.The discharge properties of the reactor operating at dc voltage in air under normal conditions are given. The results of optimizing the electrical properties are also presented. The influence of back discharges on the discharge current is discussed. The maximum discharge current density obtained during the experiment was equal to about 25 μA/cm².

The impact of fluctuating and transient kinematic and thermodynamic airflow conditions on the performance of dielectric barrier discharge (DBD) plasma actuators is demonstrated. A novel online-characterization and control approach is introduced, revealing the possibility of compensating for impaired discharge performance due to changing airflow scenarios during actuator operation. The goal of controlling the plasma actuator performance online and in situ is achieved and successfully demonstrated.

The paper deals with a new way of modifying the properties of a surface discharge. This method consists of influencing the surface potential distribution on the dielectric layer. For this, we used two configurations of plasma device. The first one is a standard surface discharge. While the second one is based on a surface discharge with a segmented ground electrode to which we added a transmission line. For these experiments, the surface discharge is supplied by an AC high voltage of a few kV with frequency ranging between 0.5 to 4.5 kHz, and operates in DBD mode. The velocity of the produced electric wind has been recorded using a pressure probe in a quiescent environment. From these measurements, the maximum velocity has been extracted and used to compare the performance of the different configurations. In addition, the voltage waveform and current-discharge, from which the power can be calculated, have also been recorded. The results highlight the capability to modify the topology of the electric wind produced by the new configuration of plasma device. The highest induced velocity achieved is 15% greater than the standard case with the same power consumed.

The paper presents experimental and theoretical investigations of electric field and charge distribution on the fly-ash layer covering the plate electrode in the back discharge in point-plane geometry. Two kinds of dielectric layer were used in the experiments: highly resistive fly-ash from an electrostatic precipitator and a dielectric plate (PET) with a small pinhole.

The properties of carbon fibers and other carbon structures produced from hydrocarbon vapours decomposed in electrically generated plasma at atmospheric pressure are studied in this paper. The electrical discharge was generated between a stainless steel needle and a plate made of nickel alloy. The carbon fiber has grown at the tip of the needle electrode, while other microflower-like deposits were built at the plate. The physical properties of carbon fibers were investigated by SEM, Raman spectroscopy, XRD, and EDS methods.

Whilst grounding is often undertaken in industry as a matter of good practice in situations where the risk of excess charge exists, little thought is usually given to the biological effects that such measures may have, or possible benefits that may arise from the more widespread application of electrostatic and other 'electromagnetic hygiene' measures in hospitals and the general built environment. Research, which is still in its infancy, indicates that grounding the human body using suitable methodologies, particularly in low electromagnetic field environments, can significantly enhance biological functioning. It is proposed that there are often a number of electrostatic and 'electromagnetic hygiene' factors that need to be addressed before the beneficial effects of grounding the human body can be fully realised in many everyday environments.

The lightning current generates a time varying magnetic field near down conductors, when lightning strikes the connected Franklin-rod. The down conductors are mounted on the wall of buildings, where residential places can be situated. It is well known that the rapidly changing magnetic fields could generate dangerous eddy currents in the human body. If the duration and the gradient of the magnetic field were high enough, the peripheral nerves are excited. In this study, the authors introduce an improved model of the interaction of electromagnetic fields of lighting current near a down conductor with the human body. The interaction model has two parts: estimation of the magnetic fields surrounding the down conductor and evaluation of health effects of rapid changing magnetic fields on the human body.

A new technique has been developed to measure the size distribution and charge state of highly charged aerosols using an Electrical Low Pressure Impactor (ELPI). The internal charger was switched alternately on and off and the time between stable charge states found to be ~ 10 s. The size distribution of aerosols was found when the charger was on, from which the charge distribution can be estimated when the charger is off using the current at each impactor stage. This method was tested in background conditions, when a candle was burning and when a negative air ioniser was used. The ELPI electrometers were not sensitive enough to accurately measure the charge state on background and candle air, but gave a value for air charged by an ioniser. Comparing results from the ELPI with other techniques showed inaccuracies in this method that need to be addressed before further use of this technique.

Polypropylene (PP) electrets with surface potential of −500V, −1000V and −2000V were prepared by constant voltage corona charging. The electrets were applied to excised rat skin for 2 hours respectively and then the skin samples were analyzed with the differential scanning calorimetry (DSC) technique to study the alteration of lipid organization of the skin. There were three peaks at 63°C, 82.7°C and 115.1°C in the DSC spectra for rat skin untreated, which have been assigned essentially to lipid, lipid-protein and protein alterations. For −500V electret treated-skin sample, only a single peak appeared at 79.1°C. With the increase of electret surface potential from −500V to −2000V, the transition temperature and peak areas at moderate decreased first and then increased. The negative electret could result in the transition of stratum corneum (SC) lipid from gel to liquid crystal and protein transition from α helix structure to β folding structure. The regulation action of electret to skin mircostructure presented an effect of "potential window".

The physical principles behind the electrohydrodynamic (EHD) actuation in microsystems is presented by reviewing five different EHD micropumps. These are classified into two groups: micropumps that exert electric forces in the liquid bulk and micropumps that exert forces in the diffuse double layer. This review of five EHD micropumps allows us to analyse the EHD actuation ranging from very insulating liquids to electrolytic solutions.

Electrospraying of solutions or suspensions provides a method for production of fine particles, in certain conditions even down to nanometer size. In the present study, electrospraying was used in drug particle production. The most important properties of the produced particles in a pharmaceutical sense are size distribution, degree of crystallinity and porosity. The size of the produced particles can easily be tailored by varying the concentration of the dissolved material, electric field strength or liquid flow rate. Most experiments on electrospraying are performed at atmospheric pressure. In the present study, the produced particles were dried under atmospheric or reduced pressure, the latter in order to improve the drying process. The effect of pressure reduction on the degree of crystallinity of the produced drug particles was studied by XRD and DSC. Also the porosity of the particles depends mainly on the drying conditions. The porosity and size of the produced particles was studied by SEM imaging.

The process of electrifying aerosol particles dispersed by a pneumatic sprayer with supersonic air flow is presented. To avoid the electric-field shielding effect, confirmed by investigations of induction charging of aerosol droplets with application of a concentric induction electrode placed in the region of liquid dispersion, the droplet electrification process following the dispersion of liquid was proposed. The supersonic atomizing head was equipped with an external high voltage contact electrode placed concentrically and perpendicularly to the droplets stream and closely to the atomizing head. Experiments were conducted in air, at ambient conditions (T = 18±2 °C, RH = 55±3%), for standard air feeding rate (0.5 m³/min, 0.4 MPa) and regulated dispersed liquid rate (0.1 – 0.55 l/min). Results of the applied electrification process, characterized by a (Q/m) factor measured as a function of liquid feed rate, have shown that the (Q/m) values achieved for post-dispersion electrification are comparable to the values obtained for typical induction electrification with application of a concentric electrode.

Electric fields induce forces at the interface between liquids with different electrical properties (conductivity and/or permittivity). We explore how to use these forces for manipulating two coflowing streams of liquids in a microchannel. A microelectrode array is fabricated at the bottom of the channel and one of the two liquids is labelled with a fluorescent dye for observing the phenomenon. The diffuse interface between the two liquids is deflected depending on the ac signal and conductivity (or permittivity) ratio between the liquids. Only a few volts are needed for observing the interface destabilization, in contrast with other electrode configurations where hundreds of volts are applied.

Electro-HydroDynamic Instability Patterning, EHDIP, is a novel micro-manufacturing process that makes use of the instability of viscous polymeric thin films when exposed to electrostatic fields. By using non uniform electrostatic fields, it is possible to shape the polymer into defined meso- and micro-scale structures which are subsequently cured to defined 2D and 3D microstructures. The relatively rapid process time, the one-step manufacturing approach, as well as the ability to produce hitherto unrealised topographies - such as continuous profile structures, makes EHDIP an attractive manufacturing process.

This paper presents a statistical analysis of 153 accidents attributable to static electricity in Japanese industry over the last 50 years. A more thorough understanding of their causes could help prevent similar incidents and identify hazards that could assist in the task of risk assessment. Most of the incidents occurred during operations performed by workers. In addition, more than 70% of the flammable atmospheres resulted from the presence of vapours. A noteworthy finding is that at least 70% of the ignitions were caused by isolated conductors including operators' bodies leading to spark discharges, which could have easily been prevented with earthing. These tendencies indicate that, when operators handle flammable liquids with any conductors, the ignition risk is significantly high. A serious lack of information regarding fundamental countermeasures for static electricity seems to be the main cause of such hazards. Only organised management, including education and risk communication, would prevent them.

When handling powders with low values of minimum ignition energy (MIE), it is often necessary to employ additional protective measures such as explosion venting, suppression, containment or inerting. Inerting generally involves reducing the oxygen concentration to around 5% v/v; however, it has been shown with gases that more modest reductions in the oxygen content can still have a significant effect on the MIE. Therefore, a test program was carried out to assess the impact of reduced oxygen levels on the MIE of a series of sensitive powders. In addition, this work was also used to investigate whether testing of such sensitive materials in the standard equipment but with reduced oxygen levels could enable the prediction of MIEs <1 mJ at standard atmospheric oxygen levels.

Accurate prediction of the probability of ignition arising from charged insulators is a crucial element of risk assessment in process industry. Incendiary brush discharges can occur when a large or grounded conductor approaches a charged insulator in the presence of a flammable atmosphere. This paper describes ignition tests based on an IEC standard method and simultaneously recorded temporal distribution of current released in the discharges, using a discharge probe integrated with the ignition probe. Ignition and non-ignition results are compared with peak discharge current and charge transferred in the discharge. No clear ignition threshold was found for either of these parameters. No major differences were found between igniting and non-igniting waveforms.

Incendiary brush discharges can occur when a large or grounded conductor approaches a charged insulator in the presence of flammable atmosphere. The probability of ignition of these discharges is essential to risk assessment in process industry. It is known that even if the total energy released in the discharge exceeds the minimum ignition energy (MIE), there may not be an ignition [1]. In a companion paper in this conference, we have reported simultaneous measurements of ignition and discharge current waveforms for brush discharges in an ethylene-air mixture in ignition tests based on an IEC standard test method [2]. In this paper we show that the resistance of the electrostatic discharge measurement system can have an effect on the peak discharge current signatures and charge transferred in the brush discharge from an insulating surface. The resistance of the discharge probe seems to affect the peak current value, but also to lesser extent the amount of charge transferred in the discharge.

Many types of granulated substances and liquids that are heavily used in industry may become easily inflammable when they are adequately mixed with air either in fine particle or vapour form. Many of these substances have very low conductivity which means that the particles can easily acquire electrostatic charge during transport or mixing operations, and the resulting electrostatic discharge may ignite the atmosphere leading to damage and even loss of life. The probabilities with which these events occur are hard to quantify. The authors present a case study and estimate the probability of ignition using FFTA (fuzzy fault tree analysis.) The result of the calculations is affected by several parameters, such as process temperature and humidity, which using suitable instruments can be easily observed. The authors thus propose a new approach where these parameters can be continuously monitored, and the fault tree evaluated in real time and early warning of the danger can be provided.

The paper analyses some ignition incidents that have been reported with insulating, (non-conductive) underground plastic pipes in retail petrol stations. The occurrence of the incidents is compared with voltage measurements, observations of the typical spread of streaming currents recorded in gasoline handling and theoretical estimates of the voltages on the pipes. The comparisons suggest that neither incendive sparks from unbonded conductors nor incendive brush discharges from insulating pipe surfaces can be ruled out although both are expected to be rare. The hazards can be prevented by using pipes with earthed conductive or dissipative inner linings.

We have measured the minimum ignition energy (MIE) of hydrogen-oxygen-nitrogen premixed gas by spark discharge. The gap distance of point-point electrode was changed between 0.3 and 1.0 mm. The effects of hydrogen and oxygen concentrations on the MIE were measured. It was 0.006 mJ for H₂ with O₂ / (O₂+N₂) = 0.35 mixture, while it was 0.017 mJ for H₂ with dry air mixture. For H₂–O₂ mixture, it was below 0.004 mJ, which was not precisely measured due to the limitation of our measurement.

Using the apparatus commonly utilized for the determination of the minimum ignition energy a series of experiments have been carried out in ethene/air as a representative of explosion group IIB. Thereby, the transferred charge as a criterion to judge the ignition potential is determined to verify the threshold of 30 nC of transferred charge given in the standard IEC 60079-0. The stored charge in a capacitance before the discharge is compared to the transferred charge in the spark. Furthermore, the correlation of ignition energy and transferred charge is examined. Based on the results presented here, the threshold of the transferred charge for explosion group IIB is discussed. Moreover, the MIE value of an ethene/air mixture is reviewed taking into account the measurement uncertainty.

In the present work, experimental results on the measurement of the total charge on a charged insulating sheet before and after a provoked brush discharge, their difference "C", the induced charge "A" when approaching an earthed microprocessor operated hand-Coulombmeter, and the transferred charge "B" at the instance of the discharge are presented. "B" is identical with the value measured by the hand-Coulombmeter within the expected measurement uncertainty. Due to observed corona losses and multiple brush discharges independent of each other, "B" correlates better with the incendivity than "C". The quotient B/C was closer to 1 than calculated in the literature but shows all predicted trends. The results obtained can be used for correct estimation of the incendivity of brush discharges between 10 nC and 90 nC. There is no need to change the existing threshold limits of 60 nC, 30 nC and 10 nC for the explosion groups IIA, IIB and IIC hitherto used in standards for zone 1.

The full electric arc discharge in gases for short gaps in homogeneous electric field and pressuredistance (pd) below 150 Torrcm, can be described as a transition between different discharge mechanisms such as: Townsend, glow, and arc. Once the arc is achieved the measured voltage drops to some volts and the current density increases several orders of magnitude. Depending upon the type of gas used, the electrode surface characteristics and type of electrical excitation, the cathode and anode voltage fall might change. The present work is directed to study the electrode fall (sum of anode and cathode falls) during a current impulse arc discharge between copper electrodes in ceramic tubes filled with argon between 0.01 and 6.5 Torrcm. The copper electrodes were cleaned, degassed and hydrogen reduced. The arc voltages were measured with fast/slow rise times and short/long duration current impulses produced by a RLC circuit. An increasing variation of the electrode fall was found at the pressuredistance range analyzed.

Electrostatic charge properties on polypropylene film have been characterized by atomic force microscopy and electrostatic force microscopy. The measurements have been carried out after the polypropylene film was electrified by contact and separation process in an atmosphere of controlled humidity. The negative and positive charge in concave surface has been observed. The correlation between concave surface and charge position suggests that the electrostatic charges could be caused by localized contact. On the other hand, positive charge on a flat surface has been observed. The absence of a relationship between surface profile and charge position suggests that the electrostatic charge should be caused by discharge during the separation process. The spatial migration of other positive charges through surface roughness has been observed. The results suggest that there could be some electron traps on the surface roughness and some potentials on the polypropylene film.

The aim of this paper is to discuss the peculiarities of the surface potential decay (SPD) curves obtained for certain non-woven media. The experiments were performed on samples of non-woven poly-propylene (PP) sheets, which are typically employed in the construction of air filters for heat, ventilation and air conditioning. The samples were in contact with a grounded plane, in order to: (1) ensure better charging and measurement reproducibility; (2) simulate the worst situation of practical interest. They were charged using either a high-voltage wire-type dual electrode or a triode-type electrode arrangement. The aspect of the SPD curves depends on the electrode configuration. When the electric field is strong enough, it can activate charge injection at the insulator-metal interface and extrinsic conduction.

The paper describes the approach of 'stutter timing' that has been developed to improve the accuracy of measuring charge decay times in the presence of noise in compact and portable charge decay test instrumentation. The approach involves starting and stopping the timing clock as the noisy signal rises above and falls below the target threshold voltage level.

We present results of finite element analysis for simple test structures which demonstrate clearly that the measurement situation is complex. The test structure consists of an open geometry parallel plate capacitor within a screened enclosure. Indeed, the presence of earthed objects, even at considerable distances, is shown to have a significant effect on the field geometry close to the source. These simulations are compared with field measurements made using an ultra-high input impedance sensor, the Electric Potential Sensor. A single experimentally determined calibration factor is all that is required to achieve excellent agreement between experimental measurements and the results of the simulations. Given this, the sensor is capable of mapping accurately, and in a non-perturbative manner, the spatial potential both within and outside of the test structure.

The aim of this paper was to assess electrostatic safety of polypropylene fabric with metallic yarns intended for use in coal mines. Such fabrics have not been used in the Polish mining industry yet. The tests conducted have been divided into two subgroups: laboratory tests and tests in a coal mine. This paper presents the results of laboratory tests, which comprise charge transfer tests, impact of washing and mechanical stress on the resistance and resistance-to-ground at the manufacturer's site. Some problems with measuring the resistance are highlighted and discussed. The results obtained allow a reliable assessment to be made of the risk of using fabrics with metallic yarns in the explosive atmosphere, which often occurs in coal mines.

The aim of this paper was to assess the electrostatic safety of polypropylene fabric with metallic yarns intended for use in coal mines. Such fabrics have not been used in the Polish mining industry yet. The tests conducted have been divided into two subgroups: laboratory tests and tests in a coal mine. This paper presents the results of tests in a coal mine, where we have focused on the resistance-to-ground in some specific situations. Bags made of fabric at the roadway face were tested, as well as the roll of fabric during transport and carried by a miner. The results obtained allow the reliable assessment of the risk of using fabrics with metallic yarns in the explosive atmosphere which often occurs in coal mines.

The electroperforation distribution in thin porous materials is investigated using the quadrat counts method (QCM), a classical statistical technique aimed to evaluate the deviation from complete spatial randomness (CSR). Perforations are created by means of electrical discharges generated by needle-like tungsten electrodes. The objective of perforating a thin porous material is to enhance its air permeability, a critical issue in many industrial applications involving paper, plastics, textiles, etc. Using image analysis techniques and specialized statistical software it is shown that the perforation locations follow, beyond a certain length scale, a homogeneous 2D Poisson distribution.

In this paper the results are presented of measurements of electrical, mechanical and chemical properties of fresh and used aircraft engine oils. Oils were used in a four-stroke aircraft engine and their samples were taken after the 50-hour work of the engine. The resistivity, permittivity and viscosity of oils were measured as a function of temperature. Additionally, some measurements of the absorbance spectra and size of particles contained in the oils were carried out. The significant reduction in the resistivity of the used Total oil was observed. The relative permittivity of both used oils was slightly increased. The oil's relative viscosity depends on temperature of oil and given time that elapsed from the very first moment when the shear force was applied in a rheometer. The results obtained allowed one to identify more precisely the chemical and physico-chemical interactions occurring in the tested samples, as compared with a typical infrared spectroscopy.

ESD Association standard test method ANSI/ESD STM2.1 – Garments (STM2.1), provides electrical resistance test procedures that are applicable for materials and garments that have surface conductive or surface dissipative properties. As has been reported in other papers over the past several years¹ fabrics are now used in many industries for electrostatic control purposes that do not have surface conductive properties and therefore cannot be evaluated using the procedures in STM2.1². A study was conducted to compare surface conductive fabrics with samples of core conductor fibre based fabrics in order to determine differences and similarities with regards to various electrostatic properties. This work will be used to establish a new work item proposal within WG-2, Garments, in the ESD Association Standards Committee in the USA.

The Giant-magnetoresistive (GMR) head suffers magnetic damage from ESD current on the order of 10 mA and thermal damage from ESD energy on the order of 0.5nJ. Contact discharge from an electrified object into a floating device was investigated as the peak current caused magnetic damage and as the energy-loss caused thermal damage. Experiments with discharges between various capacitors clarified that the discharge between 2pF-capacitors at 10V gave a peak current of 34mA and the discharge between 100pF-capacitors at 100V reached 1.5A. A 2D-plot of the peak current simulated by PSPICE indicated that the peak value arose at the order of pF and was approximately maximized at the same value of both capacitors. Theoretical energy-loss was estimated by the difference between the potential energies prior to and following the discharges. The energy-loss was 0.05nJ for 2pF-capacitors at 10V and increased in excess of 0.5nJ when both capacitors were grater than 20pF. The energy-loss reached 250nJ for 100pF-capacitors at 100V. 2D-plot of the energy-loss indicated a gradual increase as both capacitance-values increased. In order to decrease the risk of ESD failure, reducing the capacitance of the device was effective, because the transferred-charge and energy-loss were restricted.

A new on-chip detection circuit is proposed for electrical fast transient (EFT) protection design in a display system. For microelectronic products, electrical transient disturbances often cause upset or frozen states under the IEC test standard. The output signal of the proposed detection circuit can be used as a firmware index to execute system automatic recovery operations and to release the EFT-induced locked states in display panels. The circuit function to detect positive or negative electrical transients has been investigated in HSPICE simulation and verified in silicon chip. The experimental results have confirmed successful circuit performance under EFT tests. With hardware/firmware co-design, the immunity of a display system against electrical transient disturbance has been significantly improved.

Cellular polymers have recently attracted attention for their property of exhibiting a piezoelectric constant when they are electrically charged. The electrostatic charge generated in the voids by the internal discharges creates and internal macrodipole which is responsible for the piezoelectric effect. Charging by corona discharge is the most used method for cellular polymers. Many works has been published on polypropylene and polyethylene films mainly focused on the required expansion process or on the results obtained for raw cellular materials electrically activated. Our work is based on commercial polyethylene cellular films which have been physically characterized and electrically activated. The effect of thermal treatment, physical uniaxial or biaxial stretching and corona charging was investigated. The new method of corona charging improved the piezoelectric constant under other activation conditions.

Measurements of the capacitance of metal-insulator-semiconductor capacitors and the output characteristics of thin film transistors based on poly(3-hexylthiophene) as the active semiconductor and poly(vinylidenefluoride-trifluoroethylene) as the gate insulator show that ferroelectric polarisation in the insulator is stable but that its effect when poled by depletion voltages is partially neutralised by trapping of electrons at or near the semiconductor interface. Nevertheless, the combination of materials is capable of providing an adequate memory function.

Optical communication and adaptive optics have emerged as two important uses of micro-electromechanical (MEMS) devices based on electrostatic actuation. Each application uses a mirror whose surface is altered by applying voltages of up to 300 V. Previous generations of adaptive-optic mirrors were large (~1 m) and required the use of piezoelectric transducers. Beginning in the mid-1990s, a new class of small MEMS mirrors (~1 cm) were developed. These mirrors are now a commercially available, mature technology. This paper describes three advanced applications of MEMS mirrors. The first is a mirror used for corona-graphic imaging, whereby an interferometric telescope blocks the direct light from a distant star so that nearby objects such as planets can be seen. We have developed a key component of the system: a 144-channel, fully-scalable, high-voltage multiplexer that reduces power consumption to only a few hundred milliwatts. In a second application, a MEMS mirror comprises part of a two-way optical communication system in which only one node emits a laser beam. The other node is passive, incorporating a retro-reflective, electrostatic MEMS mirror that digitally encodes the reflected beam. In a third application, the short (~100-ns) pulses of a commercially-available laser rangefinder are returned by the MEMS mirror as a digital data stream. Suitable low-power drive systems comprise part of the system design.

In droplet-based microfluidics, the simultaneous movement and manipulation of dielectric and aqueous droplets on a single platform is important. The actuation forces on both dielectric and aqueous droplets can be calculated with an electromechanical model using an equivalent RC circuit. This model predicts that dielectric droplet actuation can be made compatible with electrowetting-based water droplet manipulation if the oil droplet is immersed in water. Operations such as transporting, splitting, merging, and dispensing of dielectric droplets at voltages less than 100 V are demonstrated in a parallel-plate structure. Such capability opens the way to fully automated assembly line formation of single-emulsion droplets.

In this paper a three-species two-dimensional numerical model is used for the simulation of the Trichel pulse regime of corona discharge in air in a point-plane configuration. The effect of air pressure on Trichel pulse characteristics is investigated and the numerical results are compared with the available experimental data. The effect of corona electrode radius of curvature on charge per pulse and the relation between charge per pulse and the average charge per pulse is also studied, and compared with the experimental data reported by Atten et al.

A 3D realistic numerical model of the electrostatic coating process has been developed including all relevant mechanical and electrical phenomena. The commercial computational fluid dynamics (CFD) software FLUENT was used to simulate the mechanical portion of the process. The electrical phenomena including space charge fields due to ions and poly-disperse particle charge distributions were added to FLUENT through the User Defined Function (UDF) capabilities. Selected example results are shown to demonstrate the effect of particle charge to mass ratio distributions, electrohydrodynamic flow effects and corona currents on particle trajectories and deposition efficiency. These numerical results correlate well with the theoretical expectations for static targets. In addition, an efficient method for handling 3D cases with moving flat parts is presented using the superposition principle. A procedure for extending the model for the general case of 3D moving targets is suggested.

Electrostatic precipitator (ESP) models have improved significantly in the past years. The dramatic development of the capacity of computers made it possible to increase the complexity of ESP models. Recently the different interactions between the gas, the electric field with ion space charge and the charged particles to be precipitated can be described more accurately by the newly developed complex approach. However even some of the newest computer models are limited; they are not able to follow the interactions of the complicated physical phenomena properly. For example pulse energisation of short time impulses cannot be described correctly with models assuming continuous corona current. There is another important problem, namely the examined duration of operation. Some of the models determine the trajectories of dust particles assuming that they are unchanged during the operation of an ESP. The validity of this assumption is very limited in such cases, where the development of certain phenomena is time dependent (e.g. back corona formation). In this paper the authors focus on the "long term" models, analysing such situations in which it is vital to investigate a longer period of operation of ESP-s. Using the newly developed model the effect of back corona, rapping, etc. can be analysed with higher reliability than it has been performed in previous ESP models.

A numerical method is presented for determination of higher-order dielectrophoretic forces on non-spherical particles. The method is applied to ellipsoidal particles of different dimensions subjected to electric fields with different degrees of non-uniformity. The results are compared against net force calculations using the Maxwell stress tensor method. The contribution from higher-order forces is shown to exceed the dielectrophoretic force based only on the dipole approximation when particle dimensions are comparable to the length scale of electric field non-uniformity. It is also shown that individual contributions from quadrupolar and octupolar dielectrophoretic forces strongly depend on particle aspect ratio.

In a previous paper, the authors introduced an original model for the computation of the triboelectric charges due to particle-to-particle collisions in a vibrated bed. The evaluation of the electric field inside the particle bed is a prerequisite for the accurate modelling of the tribochaging process, as it determines the trajectory of the particles as well as the charge swapping during collision. Two different approaches are presented and compared in terms of accuracy and computational time consumption. One consisted of computing the electric field as the superposition of the contributions of each point charge. The other, which proved to be much more effective, implied solving the Poisson equation for the potential generated by a given spatial distribution of charge density.

Besides the special primary lightning protection of extremely high towers, huge office and governmental buildings, large industrial plants and resident parks most of the challenges were connected to the secondary lightning protection of sensitive devices in Information and Communication Technology. The 70 year history of Budapest School of Lightning Protection plays an important role in the research and education of lightning and development of lightning protection. Among results and solutions the Rolling Sphere designing method (RS) and the Probability Modulated Attraction Space (PMAS) theory are detailed. As a new field Preventive Lightning Protection (PLP) has been introduced. The PLP method means the use of special preventive actions only for the duration of the thunderstorm. Recently several non-conventional lightning protection techniques have appeared as competitors of the air termination systems formed of conventional Franklin rods. The questionable steps, non-conventional lightning protection systems reported in the literature are the radioactive lightning rods, Early Streamer Emission (ESE) rods and Dissipation Arrays (sometimes called Charge Transfer Systems).

Evaluation of electrostatic performance of footwear and flooring in combination is necessary in applications such as electrostatic discharge (ESD) control in electronics manufacture, evaluation of equipment for avoidance of factory process electrostatic ignition risks and avoidance of electrostatic shocks to personnel in working environments. Typical standards use a walking test in which the voltage produced on a subject is evaluated by identification and measurement of the magnitude of the 5 highest "peaks" and "valleys" of the recorded voltage waveform. This method does not lend itself to effective analysis of the risk that the voltage will exceed a hazard threshold. This paper shows the advantages of voltage probability analysis and recommends that the method is adopted for use in future standards.

The 2nd part of the international standard on lightning protection (IEC 62305) deals with risk management. The explanations of the mathematical principles and the basic terms of this part facilitate the proper application of the standard. This paper gives additional information for better understanding of the standard and highlights some issues that might occur in its practical application.

Fluidized bed devices have already been used as tribochargers for various industrial electrostatic separation processes. In the present paper, the authors investigate the behaviour of polyamide – polycarbonate granular plastic mixtures in a parallelepiped bed, the height of which is roughly 2 times its length or width, so that the collisions between granules become the prevailing tribocharging mechanism. Two of the opposite walls of the tribocharging chamber consist of metallic plates connected to two DC high-voltage supplies of opposite polarities, so that the charged particles are attracted to the electrodes and separated while still in the fluidized state. The collecting hoppers are designed as Faraday cups connected to two electrometers, thus allowing the instantaneous measurement of the charge carried by the separated particles. Experimental design methodology was employed for the optimization of the tribo-aero-electrostatic separation process, the input variables being the high-voltage applied to the electrodes and the duration of the tribocharging. Higher voltages applied to the electrode system do not necessarily lead to larger quantities of collected products but improve the purity of the concentrates. The composition of the mixture influences the outcome of the process.

Electrostatic separation has already proven its efficiency as a method to recover metals and plastics from granular waste electrical and electronic equipment (WEEE). Nevertheless, there still is some work to do regarding the sorting of the various sorts of plastics (ABS, ABS-PC, HIPS, PC) contained in information technology wastes. The main objective of this paper is to optimize the electrode configuration and the operation of a belt-type electrostatic separator employed in conjunction with a new tribo-aerodynamic charging device. This application is particularly designed for the recovery of granular materials issued from shredding of computer cases, which contain large quantities of ABS. The following control variables were considered for the optimization: (i) distance between the axis of the high-voltage electrode and the surface of the grounded belt electrode; (ii) angular position of the high-voltage electrode with respect to the horizontal plane; (iii) high-voltage level. Experimental design methodology was employed for determining the optimum value of each variable, using commercial software (MODDE, Umetrics, Sweden).

In gas-solid fluidized beds as particles are fluidized, they continuously come into contact with other particles, as well as the fluidization column wall. This generates electrostatic charges by means of triboelectrification and frictional charging, leading to particle agglomeration, reactor wall fouling, and eventually process downtime and large financial losses. Grounding the fluidization column has been considered as a means of helping electrostatic charge dissipation within fluidized beds; however, in industrial applications despite the process vessels being grounded, the electrostatic problem still persists. This work focused on the effect of fluidization column grounding on particle wall fouling. Experiments were conducted in an atmospheric system consist of a 0.1 m in diameter carbon steel fluidization column. The mass and charge-to-mass ratio (q/m) of the particles that remained adhered to the column wall upon the completion of one hour fluidization period were measured in an electrically isolated and grounded columns to quantitatively determine the amount of reactor wall fouling. Polyethylene particles with different particle size ranges (300– 1000 μm) were fluidized with extra dry air at 1.5 times their respective minimum fluidization velocity (u_mf). Results obtained in the grounded fluidization column were not significantly different from those in the isolated column for all particle size ranges tested where the particles mass collected and q/m and were found to be generally similar.

The triboelectrically generated plasma discharge generated in the gap behind a sliding contact is thought to be one of the main causes of the unexplained serious tribological problems met recently in the development of advanced technologies. To solve the tribological problems arising from the triboplasma, it is essential to develop a triboplasma control technology. In this report, the effect of magnetic field on triboplasma generation is investigated as a method for developing a control technology using the Lorenz force, which acts on moving charged particles in the plasma under the influence of an applied magnetic field. Photographs of the photons emitted from the sliding contact and its vicinity were obtained with an ICCD camera while sliding a diamond pin along a sapphire disk in ambient air. By applying a magnetic field, both the distribution and intensity of the tribo-plasma changed greatly, demonstrating that a triboplasma can be controlled by applying a magnetic field.