Electrostatics Society of America

At the dawn of the Industrial Revolution, electrostatics was an emerging branch of scientific discovery. Given what we know today about electrostatics, it's hard to imagine the sense of mystery and wonder that must have confronted early experimenters such as Franklin, Kelvin, Coulomb, Faraday, Cavendish, and others. Through basic observation and deductive reasoning, these scientists developed a deep understanding of electrostatics, paving the way for the mathematical explanations recounted in Maxwell's Treatise on Electricity and Magnetism. Although electrostatics retains its status as one of the oldest branches of physics, it continues to this day to be a vibrant and ever emerging field of study that touches our lives on a daily basis. We've come to accept copy machines, laser printers, fax machines, flat panel displays, microphones, high speed printing, digital cameras, and airbag sensors—all electrostatic devices— as part of everyday life. Although modern electrostatics has its roots in the same fundamentals discovered by the early experimenters, it has been transformed into an engineering discipline with strong ties to industry and commercial applications.

In the spirit of modern electrostatics, the papers contained in these proceedings reflect a great diversity of state of the art topics in science and engineering. Indeed, individuals from other fields may marvel at the wide range of ideas that fall within the domain of electrostatics. These proceedings include papers on the use of electrostatics in imaging systems, coating processes, atmospheric probing, micro electromechanical systems, land mine detection, industrial sensors, biological pathogen control, and nanoscale particle production. Also, while much of electrostatics deals with the harnessing of electrostatic charge, a large part of the discipline deals with eliminating its effects. Several of topics in these proceedings, including papers on electrostatic discharge (ESD), charge neutralization, and web charging, address this alternative perspective.

This sixth printing of the ESA Conference Proceedings continues a tradition that started in 1994 with the help of Laplacian Press and Electrostatic Applications. Initially, ESA meetings consisted of oral presentations only, and no permanent record of the many interesting talks and presentations was available. Since its inception, the annual ESA Proceedings has become an oft cited part of the vast body of literature in electrostatics. It also has provided a means for conveying the content of the annual meeting to those individuals unable to attend. Besides providing a permanent record of the conference, these proceedings are meant to encourage further discussions and interactions among the attendees, ESA members, and members of our counterpart organizations in the United States and in other countries. May the spirit of the ESA, known by all as "The Friendly Society," continue to permeate our meetings, proceedings, social events, and technical discussions. On behalf of the Department of Electrical and Computer Engineering at Boston University, it is with great pleasure that I welcome you to the 1999 Annual ESA Conference.

For the Friendly Society, Mark N. Horenstein 1999 Conference Chair

Charges and Fields

James Q. Feng
Xerox Corporarion 800 Phillips Road, Webster, NY 14580, USA

Corona current can be generated in air or in other kinds of gas media from a thin wire enclosed in a concentric cylinder, when the voltage difference applied between the wire and the cylinder exceeds a threshold value. The threshold voltage difference for corona onset corresponds to the local electric field strength around the wire becoming aufficiently large to cause localized air breakdown or, in other words, to ionize some of the gas molecules. In the case of positive corona, i. e., the electric field is directed outward from the wire, so that negative ions in the ionization zone are drawn toward the wire whereas positive ions drift along the electric field lines toward the cylinder. A unipolar charge current is established in the drift zone where ions of one sign are dominant and those charge carriers are set in motion in response to the electric field. Although a wire cylinder system represents one of a few simplest system configurations for corona current generation, some commonly used theoretical formulas in the literature have lacked rigorous mathematical derivation and analysis

[ 1]. In the present work, a quadratic form of the relationship between corona current and applied voltage is shown to be a very reasonable approximation to the complicated exact result. However, the form of the coefficient in the present quadratic formula is quite different from that of Townsend's quadratic formula for small current

[ 1 2]. Experimental data are gathered to compare with the theory.

[close]

M. C. Lee and J. Jastrzebski
Department of Electrical and Computer Engineering Boston University Boston, Massachusetts 02215
Ph: 617 353 3363, e mail: mclee@enga.bu.edu

In this paper we discuss two phenomena of atmospheric electricity diagnosed by radars. They are (1) energetic electrons precipitated from radiation belts, and (2) dense and hot electrons induced by lightning. High energy electrons are trapped by Earth's magnetic field in the radiation belts. However, whistler waves can interact resonantly with these electrons and change their pitch angles. As the electrons fall in the loss cone of the Earth's magnetic field, they move freely and precipitate into the lower atmosphere, causing layers of anomalous ionization. Controlled study of precipitated electrons from radiation belts was conducted at Arecibo, using injected VLF waves from the ground. After the ionosphere is heated by high power O mode HF waves, large scale density irregularity sheets are generated and aligned in parallel with the meridional plane, forming multi parallel plate waveguides (viz., ionospheric ducts) for ducted radio wave propagation. VLF waves injected from the ground based transmitter, impinge at the boundary between the neutral atmosphere and the disturbed ionosphere, and effectively couple into the ionospheric ducts. When the VLF waves enter the ionosphere, they change from linear into circular polarization and propagate in the form of whistler waves. These ducted whistler waves were recorded at the magnetic conjugate point, Trelew, Argentina by a VLF receiver. Triggered particle precipitation events were monitored by a UHF incoherent radar over Arecibo. Our results show that electrons with energy exceeding 100 eV can be precipitated into the atmosphere at the o0 80 km altitudes to produce thin but dense ionization layers, giving rise to intense radar backscatter echoes.

We used S band, C band, and UHF radars to investigate the reflectivity of lightning induced plasmas, by means of radio wave scattering from electron density fluctuations. The lightning induced hot and dense electrons are modelled as long, perfectly conducting cylinders with surface density fluctuations on a scale much smaller than the total channel length. The theoretical wavelength dependence of the radar reflectivity is compared with experimental results. It is found that the theory of rough surface scattering predicts two types of inverse power law wavelength dependence for radar reflectivity. They are inversely proportional to the wavelength and the squared wavelength, which correspond to density fluctuations of lightning plasmas with a Gaussian type spectrum and a power law type spectrum, respectively. By contrast, the theory of long, thin conductors predicts a square root of wavelength dependence for radar reflectivity. The experimental observations on common lightning targets free of precipitation masking effects show a mean wavelength dependence Iying between the predictions of the two theories. It means that the wavelength dependence in these observations is bounded by these two theories. We conclude that the theory for the overdense plasma channels with irregular surfaces and the theory for long, thin overdense channels bracket the observed wavelength dependence.

[close]

A. Ustundag and M. Zahn
Department of Electrical Engineering and Computer Science Laboratory for Electromagnetic and Electronic Systems Massachusetts Institute of Technology
Cambridge, MA 02139

Kerr electro optic fringe patterns have long been used to study space charge injection and transport phenomena in highly birefringent materials such as nitrobenzene. The past experimental work has been limited to one or two dimensional geometries where the electric field magnitude and direction have been constant along the light path such as two concentric or parallel cylinders or parallel plate electrodes. For these geometries the light maxima and minima in the fringe patterns can directly be used to find the electric field magnitude and direction. In this work we calculate theoretical Kerr electro optic fringe patterns for an axisymmetric point/plane electrode geometry for which the electric field magnitude and direction vary along the light path. We compare these patterns to the fringe patterns of the two dimensional analog, blade/plane geometry. We underline the differences and study how these fringe patterns can be used to reconstruct the axisymmetric electric field components in practice. It is of interest to extend the Kerr electro optic measurement technique to point/plane electrode geometry which is often used in high voltage research to create large electric fields for charge injection at known location and at reasonable voltages.

[close]

P. Robert Kotiuga
Dept. of Electrical and Computer Engineering
Boston University

In recent decades, magnetic helicity has been identified as a conserved quantity in many plasmas governed by the equations of magnetohydrodynamics [l]. In particular, many plasmas relax to a state of minimal energy subject to the constraint that helicity is conserved. This talk begins by introducing all relevant concepts and illustrates them in the context of space plasmas. Magnetic helicity is a topological quantity and not like a conventional conserved quantity such as energy. For example, it changes sign if one considers a "mirror image" problem. For this reason, it is of great interest to compute its time rate of change in nonideal plasmas and develop a physical understanding of the result. This leads to the notion of current helicity and other "electrostatic terms". The purpose of this talk is to identify and give meaning to these electrostatic terms . [1]

Invited talks from the Chapmann Conference on "Magnetic Helicity in Space and Laboratory Plasmas" held in Boulder Colorado, July 28 31, 1998, will soon appear as an American Geophysical Union (AGU) monograph.

[close]

R. A. Sims and M. K. Mazumder
University of Arkansas at Little Rock
Department of Applied Science ETAS 575, 2801 S. University Little Rock, AR 72204
Tel: 501 569 8045, Fax: 501 569 8020 E mail: sims@eivax.ualr.edu

This paper presents the results from experimental studies of the effect of the relative humidity of the fluidization and transport air on the charging ability of powder paint. These studies measured the charge to mass ratio of acrylic automotive clear coat powders and industrial powder paint as the moisture content of the air used for fluidization and transport was varied from 0 •F to 35 •F dewpoint. Both corona and tribo charging were studied.

[close]

A Method to Determine the Surface Charge Density
of a Powder Having an Arbitrary Particle Size Distribution

Albert E. Seaver
3M Engineering Systems Technology Center
3M Center Bldg. 518 1 01 St. Paul, MN 55144 1000
Ph: (651) 733 8629 email: aeseaver@mmm. com

For safety reasons it is usually desirable to keep the charge on a powder low during transport and storage. On the other hand it is desirable to obtain a very high charge on a powder to be used in an electrostatic powder coating process. The surface charge density rTs on a particle will have an equilibrium value determined by its collisions within its environment, but this surface charge density can not exceed the Gaussian limit. As a result, the charge on a powder relative to the Gaussian limit can be used to describe the state of the powder provided the surface charge density of the powder can be estimated. Although it is relatively easy to measure the net charge Q and net mass M of a powder sample there is no known method to relate these measurements to the surface charge density as on the individual particles in the powder sample if the sample has a particle size distribution. This paper examines the mathematical relationship between Q, M and as and the results show that the surface charge density can be determined if a separate measurement of the particle size distribution is also made. To demonstrate the application of the analysis developed in this paper the theory is applied to the recent charge measurements on biological particulates discussed by Banerjee and Law.

[close]

Electrophoretic and Dielectrophoretic Particle Control
and Transport with a New Separation Apparatus

Jack Macknis Lift Feeder, Inc. Yardley, PA
Phone: 215 321 4776 Fax: 215 321 7003

Principles and applications will be presented for a new separator which diverts selected components of a fluid stream out of the main stream using electric force fields (electrophoretic or dielectrophoretic). In operation, a fluid stream is propelled axially through a three dimensional array of field gradients produced by a repetitive pattern of rods arranged at an angle between parallel and perpendicular to the initial flow direction into the separator. Those materials which are attracted or repulsed by electric field forces will move toward the outside walls of the separator because of the resultant force on them due to the combination of the force propelling them axially through the separator and the force fields set up inside the separator.

The fluid flows axially through the separator, with the wires or rods disposed within the flow volume and oriented at a given angle between parallel and perpendicular to the direction of flow of the fluid stream. The given angle is designed based on the relative magnitude of the force propelling the fluid stream axially through the separator and the forces on the selected materials due to the electric field forces between the plurality of small diameter rods. The combination of those forces and the angle of the rods produces resultant forces on those select molecules or particles sensitive to the field gradients, which are different in relation to the particle or molecules location relative to the rods. When the field gradient force has a component opposite in direction to the propelling force, the resultant force moves the particle towards the outside wall, and also within a channel formed by the electric forces and parallel to the rods, because the angle of the rods is the same as the angle of the resultant force. These particles tend to maintain the same relation relative to the rods, and remain in the channel moving towards the outside wall. When the field gradient force has a component in the same direction as the propelling force, the resultant force moves the particle to a location where the field gradient has a component opposite in direction to the propelling force or the first case.

Thus, the select molecules or particles will concentrate in the channels parallel to the rods where the resultant force is towards the outside wall. At the outside walls, partitions or slits to an outer plenum are located to divert the flow into separate plenum streams, where the select molecules or particles are removed from the main fluid stream. Advantages with this process include:

1) It is continuous with minimal contact and build up on the electrodes. The channels are formed by the force fields with no physical hardware in the flow stream. 2) A highly effective separation volume. Effect is cumulative along the length. Each volume passes through multiple capture sites. 3) Adaptable to a wide range of particles and molecules. Electric forces are produced between multiple parallel rods which can be varied in diameter and spacing to produce a wide range of gradient strength and size. This allows the process to be adaptable to a wide range of particle sizes. 4) Moves the particles outside the main flow to a separate plenum so certain problems can be worked on without interrupting the process. 5) Economically adaptable to nanoscale dimensions. Deposition on substrates possible. 6) Low energy and low pressure drop.

[close]

Sensors and Measurements

Applications of Quasistatic Sensors:
From Cure Monitoring to Landmine Imaging and Detection

Andrew Washabaugh, Yanko Sheiretov, Darrell Schlicker, and Neil Goldfine
JENTEK Sensors, Inc. 200 Dexter Ave. Watertown MA 02472
Phone: (617) 926 8422 Fax: (617) 926 8744 email: jentek@shore.net

Electromagnetic sensors that operate in the low frequency, quasistatic regime are well suited to materials characterization and defect monitoring applications. In this regime the electric and magnetic fields are decoupled and the sensor choice depends upon the properties of the materials being tested. For electroquasistatic (EQS) applications, capacitive sensing dielectrometry provides information for low conductivity materials, such as layer thickness, porosity, thermal conductivity, cure state, or the presence of defects, through measurements of the material electrical properties such as dielectric constant, conductivity, loss tangent, or complex permittivity. For magnetoquasistatic (MQS) applications, inductive sensing magnetometry provides information for high conductivity and magnetic materials, such as layer thickness, fatigue state, shot peen intensity, and crack size, through measurements of material properties such as magnetic susceptibility, electrical conductivity, or complex permeability. This paper focuses on dielectrometry applications and will describe sensor configurations and inversion methods for obtaining real time property estimates. Representative applications to be described include monitoring of epoxies during the curing transient, dielectric coating thickness measurement, monitoring of moisture concentrations in porous transformer pressboard insulation, detection of cracks in composite materials, and imaging and detection of nonmetal and metal objects such as landmines.

The capacitive sensors to be described are designed to provide measurements on a single side of a material. Electrodes are located in a single plane so that the fringing electric fields couple to the test material. In one implementation, the electrodes consist of spatially periodic interdigitated drive and sense electrodes. Since the electric field satisfies Laplace's equation, the spatial periodicity of the electrode structure or wavelength controls the penetration depth of the field into the test material and it is possible to generate a profile of the material properties as a function of depth at a given input frequency. This can be realized with multiple sets of such interdigitated structures by varying the spatial periodicity of the electrode structure or with novel electrode structures that provide multiple spatial wavelengths over a fixed sensor footprint. This approach allows for spatial profile measurements of dispersive media, where the electrical properties vary with the excitation field frequency and intensity. AISO, arrays of capacitive sensors can provide quantitative two dimensional imaging of low conductivity materials. The grid measurement methods to be described provide a real time solution to the inverse problem relating the material properties to the sensor impedance. These grid measurement methods use a database of sensor responses to map the measured signals into the desired properties for the material. The database is derived, prior to the data acquisition, using a 'forward model' of the sensor response based on either a continuum model or a finite element model for the sensor and the specific problem of interest. The measurement grids can be visualized as grids that relate measured parameters, such as the magnitude and phase of the impedance, to the unknown parameters, such as the permittivity and thickness of a dielectric layer.

[close]

Y. Du, S. H. Kang, A. V. Mamishev, B. C. Lesieutre, and M. Zahn
Massachusetts Institute of Technology Cambridge, MA 02139

The moisture diffusion process in oil free transformer pressboard is monitored using an interdigital dielectrometry three wavelength sensor in a specially constructed bench top apparatus. Experiments are performed for five different temperatures at various moisture levels. The time evolution of the moisture spatial profile in transformer pressboard is non destructively estimated. Experimental results have a good agreement with theoretical analysis of the moisture diffusion equation on the effects of pressboard thickness and temperature on the diffusion process.

The diffusion coefficient for oil free pressboard as a function of temperature and moisture concentration is estimated. Numerical methods of solving the non linear diffusion equation are developed. Literature results of the diffusion coefficient for cellulose insulation are compared and analyzed.

The interdigital sensor setup is also combined in a transformer oil Couette Facility that simulates the transformer environment for studying temperature and moisture transients in pressboard. The understanding of moisture related processes in power transformers can be enhanced with this methodology.

[close]

B.C. Lesieutre, A.V. Mamishev, Y. Du, E. Keskiner, G.C. Verghese, and M. Zahn
Massachusetts Institute of Technology Cambridge, MA 02139

In this paper we extend the continuum model for interdigital dielectrometry sensors and propose a new, direct technique for estimating material electrical properties from measurements. Interdigital sensors consist of alternating parts of long, thin electrodes on a plane. An ideal model assumes that the periodic structure extends to infinity and the electrodes have no thickness. We extend the ideal analysis to account for the physical thickness of the electrodes. We also present the model in a matrix form which is amenable to linear algebraic analysis techniques. In particular, the "inverse problem" of estimating material properties is formulated as a generalized eigenvalue problem, which avoids the convergence problems of previously used iterative algorithms.

[close]

Applied Electrostatics

lon Beam Contouring to Generate Sub Millimeter Optics

Thomas G. Bifano, Mark N. Horenstein, Mike Feinberg, Prahsant Shanbhag
Boston University 110 Cummington Street, Boston, MA 02215
Phone: 617 353 5619, Fax: 617 353~659, Pager: 888 377~801 email: bifano@bu.edu

An ion beam microcontouring process has been developed for figuring sub millimeter diameter optics, characterized by aperture diameters less than 1 um and precision of tens of nanometers or better. A novel technique was developed to create such optical contours on suitable optical materials by etching with a narrow ion beam that is rastered across a substrate. Control of the time history of the rastering can be employed to generate complex aspherical shapes. The physical setup and procedure are described, as is the mathematical contouring algorithm and a number of simulations and empirical results.

The algorithm involves a deconvolution process in which the desired removal contour and ion beam profiles are synthesized as wavelet expansions. The ion beam trajectory is then computed using a wavelet deconvolution. The ion machining process is to be carried out by focussed beam sputtering. This involves a 100 um diameter focused ion beam created by a duoplasmatron ion source. The beam is directed to the target using two orthogonal pairs of electrostatic plates controlled by a computer guidance system. The ion machining apparatus comprises an ion source, a positionable sample stage and gauging devices to monitor the conditions of the chamber and the beam.

Complex three dimensional shapes were machined in single crystal silicon and in nickel. Results characterizing ion beam behavior, system performance and contouring results are presented.

[close]

Steven F. Nagle and Jefferey H. Lang
Room 10 007, EECS Department
Massachusetts Institute of Technology Cambridge, MA 02139

This paper describes a micro scale electric induction machine that is designed to serve as the starter and generator in a micro gas turbine generator. Its development is part of the MIT Micro Gas Turbine Generator project, which has the ambitious goal of using MEMS fabrication technologies to construct compact electric power systems from a gas turbine generator comprising a compressor, combustor, turbine and electric generator. This system could exhibit a power density 20 30 times more powerful than the most powerful Lithium batteries today, based on the energy density of hydrocarbon fuel sources [Epstein et al., 1997]. It is possible that the technology could be used to create compact, portable power supplies.

This research has been aided by several previous research efforts concerning micro motors. Various types of micro motors have been given a great deal of attention in the past ten years [Tai, 1989; Lober and Howe, 1988; Bart, 1988; Mehregany, 1990]; and several types of variable capacitance micro motors have been fabricated and tested extensively at MIT [Mehregany et al., 1990; Bart et al., 1992; Tavrow et al, 1992]. We have considered all possible electric motor arrangements and chosen an electric induction machine, as shown in Figure I . At the outset, magnetic machines were ruled out due to issues of incompatibility with their fabrication processes. Also, permanent electret machines were ruled out for lack of a suitable material. And any machine which would require contact to the rotor was ruled because of fabrication and friction concerns. Only electric induction and variable capacitance remained; and variable capacitance was ruled out because of poor performance and a more difficult fabrication sequence. Like their variable capacitance counter parts, electric induction micro motors have been studied in the past [Bart and Lang, 1989]; however the research was meant only as a detailed introduction to the subject. Our efforts to date have treated the analysis and design of electric induction machines from the ground up. The goal of this research has been to develop an electric induction machine exhibiting the highest possible power density, with the highest efficiency possible, within the severe design constraints of its CMOSMEMS fabrication process and within the confines of its host turbomachinery.

[close]

J. Fernandez de la Mora and M. Gamero Castano
Mechanical Engineering Department Yale University New Haven, CT06520 8286, USA
delamora @torus.eng.yale.edu

Following the early studies by Zeleny [1] and Taylor [2] on electrified liquid cones, their richness of regimes was greatly clarified by Cloupeau and Prunet Foch, who introduced the more precise term 'conejet' [3, 4]. Research on the subject received a formidable stimulus after Fenn's discovery of multiply charged species in electrospray ionization mass spectrometry [5]. In the following decade, a number of articles have investigated the scaling laws determining the diameter [6 10] and charge [11] carried by the drops formed after breakup of these conejets. Although a number of subtle disagreements remain, there is an approximate consensus on the nature of these laws in the limit of liquids with electrical conductivities K above 10S/m, which tend to produce micron or submicron jets. This is the most interesting range for many application, since no alternative process able to atomize a liquid into such small drops is known. In this limit, the jet current l is essentially independent of liquid viscosity and meniscus voltage (within the finite voltage range where the conejet is stable), depending only on the flow rate Q of liquid pushed through the jet as well as three physical properties of the liquid: its surface tension coefficient y, electrical conductivity K, and dielectric constant.

[close]

S. Edward Law and Michael E. Diaz Department of Biological and Agricultural Engineering
Driftmier Engineering Center University of Georgia Athens, GA 30602 4435, USA
Email: edlaw@bae.uga.edu

A fundamental need of all societies worldwide is an adequate and safe source of food. Consumer conf~dence in food safety has become of paramount importance, while at the same time to remain competitive and environmentally sound, the US food processing industry must conserve input resources and more effectively treat process wastewaters. Over the past ~8 years the use of chlorine based treatment of certain process waters has raised concerns regarding inadvertent formation of carcinogenic chlorinated hydrocarbon compounds (e. g., trihalomethanes) in the water. Consequently, major water users such as the pulp and paper industry are relying less on chlorination and are phasing in alternative treatments—principally ozonation

[close]

Mark N. Horenstein
Dept. of Electrical and Computer Engineering
Boston University 8 Saint Mary's St. Boston, MA 02215 USA
Ph: 617 353 9052 Fax: 617 353 6440 email: mnh@bu.edu

A lumped element model has been used to explain charge conduction and convection in stationary and moving web systems. Incremental sectors of the web are assigned conductance and their individual potentials are computed. Ordinary circuit equations are used to determine the evolution of the charge distribution. Results compare favorably with the analytical solutions of other authors.

Electrostatics plays an important role in the processing of textiles, polymers, plastics, and other insulators. Large sheets of these materials are commonly called "webs." When a thin web of insulating material is drawn over metal rollers or similar guiding structures, contact electrification can cause excess charge to build up, leading to arcing, electrostatic discharge (ESD), unwanted electrostatic forces, or undesirable dust precipitation. The electrostatics of a moving web system is a dynamic problem affected by surface conductivity, surface layer capacitance, geometry, and material motion. An analysis method that predicts the charge distribution and surface potential on a moving web can be a valuable tool when designing web based manufacturing systems, but direct mathematical analysis becomes difficult in the complex geometries found in many practical industrial situations. This paper describes an analysis method based on a discretized, lumped element representation of moving webs. Charge conduction is modeled using fixed value resistors, and charge convection is modeled by direct material transport over time. The analysis method can be applied to a wide variety of geometries and industrial situations and provides physical insight into the fundamental electrostatic processes at work in moving web systems. It also should be useful in predicting the behavior of web systems in which surface conductivity is non ohmic (i. e., nonlinear.)

[close]

Humphrey Wong
Surface Modification ar1d Electrostatics Unit, MR&E, IMMPC
Eastman Kodak Company Rochester, NY 14652

Printers often employ pinch rollers in order to convey sheets of material from storage cassettes, through a printing operation, and sometimes through a development station before finally depositing the sheets into a receiving area. Transport of sheets through pairs of pinch rollers can result in tribocharging both the rollers and the sheets. By monitoring the end shafts of certain types of pinch rollers with voltmeters, it is possible to relate the voltage vs. time behavior to the tribocharging taking place during passage of the sheets through the pinch rollers. In this paper, we will present an interpretation of various voltage signals in terms of the charging and discharging characteristics of the roller and sheet surfaces.

[close]

Jiu sheng Huang
9th Department
Beijing Research Institute of Special Electromechanical Technologies
No. 1, Bei yuan Da Yan, An Ding Men Wai Beijing, China, 100012
Tel: 86 1~66749396~5 E mail: jiushuang@263.net

This transient electric field radiated from charged human body discharging to the ground and from the ESD simulator are studied. Many waveforms and spectrums of the field from the ESD are analyzed. The effects of the field to typical electronic circuits are studied.

[close]

Andreas Trupp atrupp@hotmail.com

It is demonstrated that two common methods of determining the mechanical force acting between two electrified bodies, that is Coulomb's law on the one hand, and the method of virtual work on the other hand, yield results that differ from each other if dielectrics are involved.

[close]

Hasashi Shio
Department of Physics, Hokkaido University, Japan
Fax: 81 11884 6184

Charging mechanisms of ice are generally based on the temperature gradient theory in which the electric potential is formulated as V = 2~1T (mV), where V is a electric potential difference between two specimens, and T is the temperature difference between them. If the temperature difference is 30 •C, the electric potential difference becomes only 60 mV. On the other hand, when two ice specimens are asymmetrically rubbed together the electric potential difference reaches to above I V. As a result, it is suggested that the charging mechanism is based on a different origin from the temperature gradient. In order to research this new origin of the charging mechanism of ice, the dependence of the charging phenomena of ice on stress of the specimens is investigated.

[close]

Pellumb G. Berberi
Department of Physics Polytechnic University of Tirana Tirana, Albania

A new multiple step method for measuring electrical resistivity of textile assemblies is proposed that takes compressional properties of the assembly into consideration. A new parameter is introduced to describe electrical resistivity of textile materials as the limit resistivity of a compressed fiber assembly. This new definition approaches the measured resistance of the textile assembly as something similar to the volume resistivity of a rigid homogeneous material. Experiments carried out with different kinds of fiber assemblies clearly show that the electrical resistivity so defined is an inherent characteristic reflecting the. and is independent of sample form (fabric, yarn, fiber).electrical properties of fiber material.

[close]

Pellumb G. Berberi, J. Amirbayatt, I. Poratt
Department of Physics
The Polytechnic University of Tirana Tirana, Albania TDepartment of Textiles, UMIST Manchester, UK

The true area of contact of two surfaces is an important parameter to be estimated when electrostatic propensity, surface resistivity, frictional resistance, or any other property of the surfaces are to be measured [1, 2, 7]. Some methods for testing of electrostatic properties of textiles as 'decay time,' 'frictional charge' or 'electrical surface resistance' are known, among others, for their low reproducibility due to the uncontrolled alteration of 'true area of contact' [3, 6].

Several attempts have been reported by different authors for the estimation of the area of apparent contact between metal and a flat polymer sheet by measuring the imprint made on the polymer surface by a travelling microscope [4, 5]. Naturally, this method can not be used to estimate the area of contact of a textile fabric with a flat rigid surface because of relatively high surface asperities. To the best of authors' knowledge, there is no work published which describes the objective measurement of contact area of a textile material with a flat rigid surface.

[close]