Electrostatics Society of America

Abstracts from the ESA 2000 Annual Conference Proceedings

June 19-22, 2000

2000 Brock University
St. Catherines, Ontario

Joseph M. Crowley

Electrostatic Applications
Morgan Hill, CA 95037
electro@electrostatic.com

Electrostatics is a field with many applications, and it is often difficult for one person to gain an understanding of all the various lines of inquiry that are taking place. In order to discover where electrostatics work is carried out in the United States, a number of lists of people active in electrostatics were analyzed and compared. These lists involve participants in meetings, members of organizations, authors, and customers of an electrostatics bookstore.

This analysis shows that active participation in electrostatics is much more widely dispersed than might be obvious from any individual's direct experience. Although there are a few large clusters of organizations like Xerox and Hewlett-Packard, most of the workers are in much smaller organizations spread out over all the states, with little apparent interaction.

In addition, most people appear only on a single list, suggesting that these lists are merely small samples from a much larger population. Using techniques adapted from population biology, the overlap of the lists is used to estimate the total number of people in the USA working in electrostatics. The number is probably in the tens of thousands. Some of the implications of these results for the future of the ESA are discussed.

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Importance of Electrostatics in Respiratory Drug Delivery

Joanne Peart, Ph. D.

Virginia Commonwealth University
Richmond, VA

Respiratory drug delivery has historically disregarded the subject of electrostatics. Models of aerosol deposition in the human lung are based on data collected following inhalation of `charge neutralized' aerosol particles (Task Group on Lung Dynamics, 1966), despite studies which have shown dramatic deposition changes as a function of aerosol charge (Melandri, 1983; Balachandran, 1991; Bailey 1997).

Recently, the paradigm has changed, as aerosol electrostatics represents an important and emerging property of pharmaceutical aerosols. Therapeutic aerosols generated by nebulizers, pressurized metered dose inhalers (pMDIs), and dry powder inhalers (DPIs) are known to be charged. Moreover, the practical significance of electrostatic charge interactions to the functionality of therapeutic aerosols embraces most aspects of their processing and general use, including their formulation and manufacture, dosing reproducibility and deposition behavior within the respiratory tract and/or spacer devices. Electrostatic properties of the potentially respirable aerosol clouds generated by high efficiency DPIs (Turbohaler© and Dryhaler©) have been shown to be dependent upon the physical and chemical properties of the powder under investigation, as well as the construction and deaggregation mechanism of the inhaler (Byron, 1997). Figure 1 illustrates the net fine particle dose charge of aerosols generated by commercially available pMDIs. Both albuterol chlorofluorocarbon (CFC) and hydrofluoroalkane (HFA) MDIs conferred net electronegative charges on their fine particle clouds of the order of -160 pC, despite their different propellant systems, drug salt forms, drug concentrations and metering volumes. A systematic investigation of the formulation components' contribution to the measured charge showed significant differences between the CFC and HFA based albuterol systems (Peart, 1998). Electrostatic charges of respirable particles determined in these studies have enabled us to speculate whether such charged particles would be expected to influence regional drug deposition in the respiratory tract.

M. Kashef, S. Chrai, A. Katdare, R. Murari, G. Santonastaso

Delsys Pharmaceutical Corp.
Princeton, NJ

AccudepÆ technology is a manufacturing process based on electrostatic deposition. This technology provides a simple manufacturing process for deposition of active pharmaceutical drugs on a multitude of substrates. Majority of active pharmaceutical drugs is in the form of dry powders with different morphologies varying in size from sub-micron to greater than 100 microns. Using these powders as primary raw material, traditional pharmaceutical manufacturing applies a sequence of manufacturing operations that consists of mixing and blending powders, granulation, drying, lubrication, compression and coating. Each step requires employment of strict quality control procedures that add cost and cycle time without adding any value. The final product, also known as finished dosage form, consists of a small amount of therapeutically active drug substance, mixed with a large quantity of inactive excipients. AccudepÆ technology replaces all these steps with single electrostatic deposition process equipment and eliminates most of the inactive excipients.

In AccudepÆ technology pharmaceutical powders are transported from the hopper to the next unit wherein electrostatic charging of the powder takes place. Subsequently, the powder is moved to the next module, which disperses the powder into a homogeneous and uniform cloud of particles. These charged particles accelerate to the opposite end of the chamber and deposit on predetermined areas of a receiver covered with a pharmaceutically acceptable polymer film. The receiver is a planar surface consisting of a ground plane surrounding a matrix of deposition electrodes. These individual electrodes are ultimate resting-places of the pharmaceutical powders that have entered the chamber. These deposition electrodes are electrically insulated from the ground plane by dielectric media. By applying the proper potential between the electrodes and the ground plane one can direct charged pharmaceutical particles to the deposition sites.

Actual mass and bioavailability of the active drug in any dispensed medicine determines its efficacy. The efficacy can vary from minimal to therapeutic target or even toxicity depending on the dose of the administered drug and the patient. Measuring active drug content of finished dosage form is a destructive, and expensive, test process. Hence, current regulation allows manufacturers to use random sampling and well-defined statistical methods to pass or fail batches. Due to the nature of this test process, batches of drugs are released to the market that are recalled later. This process costs tens of millions of dollars, not to mention adverse effects on patients.

AccudepÆ technology enables manufacturing of drugs with much higher accuracy and provides an economical way for nondestructive testing of the product that can be used to measure the active drug content of every individual dose.

Pharmaceutical powders have a wide range of physical, electrical, chemical and mechanical properties. Active research is conducted to develop metrics for measuring those powder characteristics that play a role in AccudepÆ process. Knowing these parameters will enable us to fine-tune the process to each drug and create a recipe that can be used to optimize manufacturing process. Furthermore, it will provide the road map for future enhancements to the design and manufacturing of the machinery used in AccudepÆ process. Several pharmaceutical powders have been characterized and successfully deposited using AccudepÆ technology. The dose amount for these depositions varies from micrograms to several milligrams. These depositions have been processed into final dosage forms with different formats, including those used in current pharmaceutical manufacturing.

Compatibility studies have shown that AccudepÆ technology can improve drug stability thereby creating new or expanded commercial applications for new or current drug products.

Animal studies have produced successful results for the technology and human studies will be conducted before the end of the current year. The research and development in this technology is conducted by Delsys Pharmaceutical Corp. in close collaboration and partnership with major pharmaceutical companies in the US and Europe.

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L. John Gagliardi

Department of Physics
Rutgers University
gagliard@crab.rutgers.edu
Tel: 856 225 6159

Primitive biological cells had to divide with very little biology. This paper proposes physicochemical mechanisms based upon microscale electrostatics which explain and unify the basic motions during mitosis (nuclear division) and cytokinesis (cytoplasmic division):

(1) assembly of the asters,
(2) motion of the asters to the poles,
(3) poleward motion of chromosomes (anaphase A), and (4) cell elongation (anaphase B).

In the cytoplasmic medium which exists in biological cells, electrostatic fields are subject to strong attenuation by ionic screening, and therefore decrease rapidly over a distance of several Debye lengths. However, the presence of microtubules within cells changes the situation completely. Microtubule dimer subunits are electric dipolar structures, and can act as intermediaries which extend the reach of the electrostatic interaction over cellular distances.

Experimental studies have shown that intracellular pH rises to a peak at mitosis, and decreases steadily through cytokinesis and furrowing. This result, in conjunction with the electric dipole nature of microtubule subunits, is sufficient to explain the dynamics of the above motions, including their timing and sequencing. In addition, the model can also be extended to incorporate the complex motions during prometaphase (congression) and alignment at the metaphase plate. In order to keep the discussion within manageable bounds, prometaphase motion will not be addressed in this paper. The physicochemical mechanisms utilized by primitive cells could provide clues regarding our understanding of the important problem of cell division in modern eukaryotic cells.

Steven C. Cooper¹ and S. Edward Law²

¹Electrostatic Spraying Systems, Inc.
Watkinsville, GA

²The University of Georgia
Biological and Agricultural Engineering
Athens, Georgia

An improved air-assisted induction-charging electrostatic spray nozzle has been jointly developed by The University of Georgia and Electrostatic Spraying Systems, Inc. This spray charging nozzle is for liquids with resistivity in the range of between 25 ohm-cm to 10 megohm-cm. Charging levels achieved are 5 to 10 mC/kg for liquid flow rates in the range of 80 to 200 ml/minute. Primarily the charging nozzle was intended for water-based agricultural pesticide and foliar fertilizer applications onto plant targets. Various large agricultural spray machines have been developed and are now being sold commercially. The largest of these tractor-mounted field sprayers have over 100 electrostatic nozzles. Over one million acres of cropland are now routinely treated with electrostatic field sprayers using this new technology. Growers typically use half the amount of pesticide compared to conventional spraying methods. Other agricultural applications include sprayers for postharvest bananas and vineyard spray systems for wine and table grapes.

In addition to agricultural applications, several unique industrial applications have recently been developed commercially. Perhaps the most unique is the new cosmetic skin tanning system. This electrostatic sprayer dispenses a lotion evenly over the skin, resulting in a cosmetic tan in about one minute while eliminating the concern of hazardous ultraviolet radiation associated with other skin tanning methods.

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Sheryl A. Barringer and Peggy Miller

Department of Food Science and Technology
The Ohio State University
2121 Fyffe Road
Columbus, OH 43210

Electrostatic coating technology was introduced to the metal painting industry in the 1960s. The solvent-based liquid paints were converted to dry powders containing pigments, binders, fillers, and hardeners. By applying the powdered paint using electrostatic spray guns, and melting that powder onto the metal, a more even coating is produced. Research on electrostatic technology has been taken from powder coating in the painting industry and adjusted to suit the food sector (Anon., 1996).

Snack foods such as potato chips, pretzels, popcorn and tortilla chips are coated with salt, cheese powder and assorted seasonings. The amount of seasoning is very important to the consumer, so the producer has to make certain the snacks are completely and evenly coated on all sides. Powders used for coating snack foods are applied by means of sprinkling systems such as rollers, screw distributors and anti-static atomization systems (Anon., 1993). The equipment can be very complex or as simple as seasonings dropping from a pipe into a tumbling drum. These methods prove to be very haphazard and often result in a poor distribution of flavor onto the product, severe flavor overuse and contamination of conveyors and weighing equipment (Anon., 1996; Pannell, 1980). With traditional seasoning methods, it is not uncommon for a snack manufacturer to put 30% and, in some cases, as much as 50% more seasoning than actually needed into a drum because of the expected waste incurred with these types of seasoning processes (Anon., 1992). This waste becomes an economic concern due to the high price of seasonings used on snack foods.

The basis of electrostatic coating is the attraction between the negatively charged seasoning, in this case the salt, and the nearest earthed object, the food product (Anon., 1980). The seasoning is dispersed from a tube and introduced to a charge created by a wire. When the seasoning passes through the corona zone created by the charge on the wire, the seasoning picks up the charge and seeks out the nearest ground state, the product to be coated or the drum.

The charged particles are allowed to fall onto the product, where they tend to separate and distribute themselves evenly. This separation and distribution is caused by the charges on the seasoning repelling each other. Electrostatic attraction helps to achieve a more homogenous coating even on difficult shapes and gives a considerable reduction in flavor falloff (Anon., 1996).

Using electrostatic coating methods eliminates the problems associated with traditional coating methods. However, the size and the shape of the coating material may have a large effect on the transfer efficiency when using electrostatic coating methods (Mazumder et al. 1997). A more efficient electrostatic coating system provides more seasoning to the food product with less wasted seasoning. The purpose of this study was to determine the effect of seasoning size and shape on efficiency of electrostatic coating.

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Charles G. Noll

ITW Static Control and Air Products
2257 North Penn Road Hatfield, PA 19440-1998
Tel: 215-822-2171, Fax: 215-822-3795
email: ir000382@mindspring.com

Current-voltage (I-V) data for positive and negative polarity point-to-plane geometries are reported for gas flows transverse to the axis of the emitters. Air and nitrogen flows from zero to 5 m/s were considered in the experiments and temperatures from 213 K to 493 K in nitrogen and 283 K to 493 K in air. Carrier entrainment from the individual corona and positive-negative polarity emitter-pairs were considered towards understanding the static elimination process.

Charles G. Noll

ITW Static Control and Air Products
SIMCO Static Control and Cleanroom Products
2257 North Penn Road
Hatfield, PA 19440-1998

Charge decay has been studied in a cylindrical flow channel with a pair of point-to-plane emitters. It was found that charge decay is determined by the type of corona and gas speed, and not so much by the magnitudes of the corona currents.

Charles G. Noll¹, William Miller²and Christopher Bracikowski²

¹ITW Static Control and Air Products
2257 North Penn Road
Hatfield, PA 19440-1998

²Department of Physics
Bloomsburg University
Harltine Science Center
Bloomsburg, PA 17015

Unlike electrical corona, radioactive ionizers produce positive and negative carrier pairs in the absence of an external electric field. In this work we study the entrainment and extraction of carriers from an air or nitrogen stream that is blown over ionizer. The results are compared with those from corona ionizers where electric fields are used to generate and strip carrier species from the gas stream.

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J. A. Gonzalez

Department of Clothing and Textiles
University of Manitoba Winnipeg, MB, Canada, R3T 2N2
Tel: (204) 474-8065, Fax: (204) 474-7592
E-mail: gonzale0@ms.umanitoba.ca

This paper describes the development of a theoretical model for characterizing textile fibers in terms of charge dissipation. Charging and decay of charge are considered a function of time and time constant of the material. Twenty-four fabrics with different fiber content and blends were evaluated and characterized at 30% relative humidity and room temperature. A charging-dissipation model was developed identifying five parameters on a waveform. Various theoretical considerations have been drawn in explaining why textile fibers yield distinct dissipation waveforms. Relationship among polymer structure, fiber moisture content, environmental conditions, and the identified five parameters of the proposed charging-dissipation model has been determined.

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J. M. Singley, V. J. Urick, C. Bracikowski, and C. G. Noll

¹ Department of Physics
Bloomsburg University
Hartline Science Center
Bloomsburg, Pennsylvania 17815-1301

² ITW Static Control and Air Products
2257 North Penn Road
Hatfield, PA 19440-1998

The elimination of static charge from corona-treated articles has been a challenge for many years, yet few systematic investigations have been reported. In this preliminary report we summarize literature and present early experiments and modeling efforts towards understanding the distribution of charge on cylindrical bottles before and after corona treating. The results are discussed in terms of Gauss's Law and several static elimination approaches.

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Dan A. Hays

Xerox Corporation
Wilson Center for Research & Technology
Webster, NY 14580 USA

Copying and printing technologies based on electrostatic marking have evolved to high levels of performance over the past 40 years. Xerography is the dominant electrostatic marking technology with an estimated 50 billion dollars a year in worldwide revenues. The invention of xerography by Chester Carlson on October 22, 1938 was the genesis of a major innovation during this century. Carlson's invention was influenced by the earlier work of Paul Selenyi, a Hungarian physicist, who was the first to record images with an electrostatic marking process in which a modulated ion source was scanned over an insulating layer to form an electrostatic image that was subsequently developed with powder. Carlson's insight was to use a photoconductive material to produce an electrostatic image that is then developed with charged, pigmented powder. Carlson built a prototype of a copying machine, but was unsuccessful in attracting the interest of large corporations. In 1944, Battelle Memorial Institute in Columbus, Ohio began work on the process where key advances were made in materials and processes. This led to the introduction of the highly successful Xerox 914 plain paper copier in 1959.

Electrostatic marking technologies utilize an electrostatic force acting on pigmented particles to form an image that is deposited on a medium such as paper. The electrostatic force can be approximated as where is the charge on the particle and E is the applied electric field. To form an image with charged particles, a variation (spatial or temporal) in the electrostatic force is required. For insulating particles, the variation in can be expressed as . The first term describes a class of imaging physics in which a variation in E acting on charged particles causes an image-wise variation in the electrostatic force. The xerographic process is a good example of the imaging class in which the spatial variation in dE is produced by image-wise light exposure of a charged photoreceptor. The imaging class has not been commercialized. If the pigmented particles are conducting and in contact with an electrode or other conductive particles in the presence of an electric field, a charge will be induced on the particles that is proportional to the applied electric field. This represents a third class of imaging physics in which is proportional to the square of . Several types of electrostatic marking systems based on the above classes of imaging can be identified for either indirect or direct printing onto paper [Hays, 1999].

The current high levels of performance for electrostatic marking systems can be attributed to a multitude of material and process advances. The quality of images depends on the control of toner particle charge and adhesion. Triboelectricity is the dominant method for charging particles, in spite of a poor understanding of microscopic mechanisms and the enhancement of adhesion due to a nonuniform surface charge.

V. I. Struminsky

Sobolev Institute of Mathematics
Novosibirsk, Russia

For measurement the strength of a slowly varying (quasi-static) electric field, usually electrostatic fluxmeters (field mills) with dynamic transformation of field strength into AC-signal are used. Two main versions of the marked devices with cylindrical and flat measuring electrodes are known. The operation of these devices is based on periodic modulation of the electrode area exposed to the field under measuring by means of electrode rotation or periodical shielding by a rotating screen. New kinds of dynamic transformers-electric field sensors recently are developed, at which the vibration of electrode is used instead of the rotation. In some fields of application these sensors have advantages in comparison with traditional fluxmeters. Absence of rotating parts and leak-proofness of transformers leads to appreciably longer original life, that is important for long-time monitoring, for example, in atmospheric and geophysical experiments. High frequency of transformation, small area of the electrodes and practically complete absence of electrode area modulation-all these allow using vibrational sensors for measurements in medium with a high electrical conductivity and convective current. In this paper theoretical basics of transformation process on an example of the sensor are presented, at which the modulation of an electric field occurs by vibrating string resonator. The example of concrete model of the sensor is given which was originally designed for thunderstorm electricity observation and then was used also for continental and oceanic investigations of good weather atmospheric electricity. The brief description of a miniature electric field sensor is given which was designed by a group of researchers of Novosibirsk State University for control of spacecraft surface charging and space electricity research and successfully used in space investigations.

Operating conditions of measuring equipment in industrial applications are usually not so strong than in a free atmosphere or in space. The vibrational sensors can widely be used for the control of electrostatic effects and hazards in various industrial instrumentations.

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Liviu Matei, Mihai Antoniu, Cristian Ze, Gh. Antoniu

Technical University
"Gh. Asachi" Bd. D.
Mangeron 53 Iasi
6600, Romania
lmatei@ee.tuiasi.ro

The paper presents a fieldmill electrostatic transducer with two output signals from field sensor. The output signals are sinusoidal voltages with the same frequency but have opposite phase. A differential amplifier DA sums these voltages and subtracts parasitic voltages. The output voltages of DA have the same frequency but double amplitude and very small parasitic components. Proposed solution was tested on portable model (gun-like).

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J. C. Lee¹ , W. R. Young² , J. J. Liou¹, G. D. Croft² , and J. C. Bernier³

¹Electrical and Computer Engineering Department
University of Central Florida
Orlando, FL 32816

²Technology Development Department
Intersil Corp.
Melbourne, FL 32902

³Reliability Engineering Department
Intersil Corp.
Melbourne, FL 32902

Transmission line pulsing (TLP) is a useful technique to characterize electrostatic discharge (ESD) events in semiconductor devices. The pulse waveforms generated by a traditional TLP setup, however, are often distorted by signal reflections. In this paper, a new and simple experimental setup is developed to improve the waveforms and deliver higher current to the device under test (DUT). The setup employs a modified voltage probe and a R/2R termination network.

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John Chubb

John Chubb Instrumentation
Unit 30, Lansdown Industrial Estate
Gloucester Road
Cheltenham, GL51 8PL, UK.
Tel: +44 (0) 1242 573347 Fax: +44 (0) 1242 251388
email: jchubb@jci.co.uk

Materials can be assessed for risks from static electricity by measurement of `charge decay' and by measurement of `capacitance loading.' This paper describes appropriate experimental methods for these measurements and reports the results of studies on a variety of materials in various test conditions.

V. I. Struminsky

Sobolev Institute of Mathematics
Novosibirsk, Russia

From methodological point of view electric field measurements in the strato-mesosphere are match more difficult than at the ground level. It is in general because of the influence of various environment factors on the measurement process. The main factors are the motion of an electric field sensor relative to the medium, complex composition of charged particles, varying air conductivity, presence of streams of energetic particles and UV-radiation and so on. In this paper some methodological aspects of electric field measurements in conductive medium in the presence of displacement, conductive and convective currents are discussed. Basic principles of theory of "double probe" method are considered in the presence of probe rotation. Some recommendations for reducing the influence of the last two components of complete current on the accuracy of measurement results are proposed.

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John Chubb and John Harbour

John Chubb Instrumentation
Unit 30, Lansdown Industrial Estate
Gloucester Road
Cheltenham, GL51 8PL, UK.
Tel: +44 (0) 1242 573347 Fax: +44 (0) 1242 251388
email: jchubb@jci.co.uk

The design and performance of a system is described to provide advance warning of the risk of local lightning on the basis of observations of atmospheric electric field, radio noise and lightning impulse signal activity. The values of these parameters are assessed to provide two levels of warning.

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Matti Murtomaa¹ and Ensio Laine

Laboratory of Industrial Physics, Department of Physics
University of Turku, FIN-20014 Turku, Finland
Tel.; +358-2-333-5735; fax: +358-2-333-5993.
E-mail address: matti.murtomaa@utu.fi
¹Corresponding author. Also Graduate School of Materials Research, Turku, Finland.

This paper presents the results of an experimental study on the triboelectrification of glucose powder in a glass pipe, and the role of smaller particles of different material mixed with the main phase. Mixtures of different concentrations were charged by sliding them down into the Faraday's cup via a glass pipe. The influence of sticking to the inner surface of the pipe was examined with a microscope equipped with camera and an image analysis program. Smaller particles at the pipe surface partly change the glucose-glass-contacts to the glucose-adhered powder-contacts and this has a significant effect on the sign and the amount of transferred charge. The relative coverage of the glass pipe by small particles can be used as a measure of the charging ability of an additive, and can also give information of the sufficient amount of additive which would lead to neutral charge.

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T. S. Lee

Department of Electrical and Computer Engineering
University of Minnesota Minneapolis, MN

Potential scanning was earlier used to measure long-term charge retention behavior on a dielectric sheet following the onset of positive point corona. A thin oil film provided visualization, showing circular domain structure in expansion. Being repeatable, this phenomenon has been further studied by scanning sequences consecutively and separately obtained in intervals of a few seconds. The results are consistent with projections of a self-limiting evolutionary charging theory previously considered.

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Albert E. Seaver

3M Engineering Systems Technology Center
3M Center Bldg. 518-1-01
St. Paul, MN 55144-1000
Tel: (651) 733-8629 Fax: (651) 736-3122
e-mail: aeseaver@mmm.com

Electrostatics is often used to control the motion and placement of small particles. In many applications a broad distribution of particles is first "cut" into a narrow particle size range by sieving or screening. This group of sieved particles becomes the particle distribution used in the application. In these situations the average particle diameter in the cut, which is not much different from the largest or smallest diameter particle, becomes the effective particle diameter used in the electrostatic calculations. However, when particles are sieved or screened their size is most often listed by the size of the mesh or screen used to classify the particles. This leaves the person about to make a calculation scurrying around trying to find the conversion between the screen size and the actual particle size.

For example, the average particle size of a "cut" is most often referred to as the grit (or grit size or grit number) or interchangeably as the mesh (or mesh number) or simply as the grit mesh. In this paper a comparison table is presented listing the average particle size and mesh number values for various standards (ANSI, FEPA, ISO, JIS and the Tyler Standard Screen Scale) in use today. Based on the definition of the mesh number a simple model of the sieving or screening process is presented. The model is used to give a mathematical relationship between average particle diameter and grit size or mesh number for a cut. The simple relationship [or ] is shown to predict (30%) the connection between the average particle size and the grit or mesh number M for all the screen standards when the particle size is large (> 80 m), and this relationship is also found to be reasonably accurate for micropowders described by the FEPA-P standard.

H. Zhao, G. S. P. Castle, and I. I. Inculet

Applied Electrostatics Research Centre
Department of Electrical and Computer Engineering
University of Western Ontario
London, ON, Canada, N6A 5B9

Experimentally it was found that when a sample of bipolar charged powder was freely dropped from a height, the charged particles would separate in vertical and horizontal directions. The separation was based on the charge, size and mass of individual particles and other particles around them. A computational model was developed by Ali to model the dropping process of a batch sample of powder poured vertically from a height [1]. This model was extended here to simulate the separation processes of free falling charged particles passing through a vertical cascade array of Faraday pails. The difference with Ali's work [1] was that the boundary constraint imposed by the vertical Faraday pail array was introduced in the model since the movement of the bipolar charged powder was restricted by these boundaries during the falling process. The model presented here takes into account electric al, drag and gravitational forces acting on each particle.

In the experiments, the vertical array of Faraday pails consisted of seven Faraday pails, six special Faraday pails and one normal one, which were mounted vertically in cascade. The normal Faraday pail was located at the bottom. Each Faraday pail consisted of an inner cylinder and an outer cylinder pail. The inner and outer pails of the special Faraday pails had open holes on the upper and lower covers.

The vertical array of Faraday pail sensors can be used to partially separate the bipolar charged polydisperse powder and measure the charge to mass ratio (Q/M) distribution of the powder deposited in each Faraday pail. The separation forces are due to the gravity segregation and space charge repulsion. Depending on the trajectories of particles in the free falling processes of the bipolar charged polydisperse powder, the particles were selectively collected in the vertical array of Faraday pails according to their charge, size, and mass thus providing a measure of the Q/M distribution of the charged particles. In the experiment, the particles were charged in an earthed metallic fluidized bed, selectively sampled at different depths of the bed through an axial sampling tube and dropped through the vertical array of Faraday pails. Three kinds of commercial polymer powders were used, referred to as A, B and C. Powder A, B and C are all polyamide powders. Powder A and B contain 3% of TiO2 as an extraparticulate additive and 0.48 ppm of chemically combined pigments. Powder A is the original powder from the packed powder bag and powder B is obtained from the industrial fluidized bed after working for a long period time. Powder C contains 8% of TiO2 chemically combined with the polymer.

This model is compared to the experimental results and further documents the presence of bipolar charging of polymer powders in fluidized beds. Experimental results show that even though the net charge may be positive (C) or negative (A, B), the smaller particles are charged negatively and possess high Q/M value, while the larger particles are charged positively and possess lower Q/M.

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Ivan J. S. Lopes, Shesha H. Jayaram, and Edward A. Cherney

University of Waterloo
Electrical & Computer Engineering Department
Waterloo, ON, Canada

The use of polymeric materials for outdoor insulation has increased continuously in the last few years mainly because of their improved performance under wet and contaminated conditions when compared to conventional porcelain and glass technology [1]. This is due to their hydrophobic surface property, which prevents water filming and development of leakage current. Because of their hydrophobicity, polymer outdoor insulators are partially wet more often than completely wet, and their flashover mechanism, in some cases named sudden flashover, is different and yet not well understood [2-4].

In this work, the problem of the field distortion along a partially wet insulating surface is addressed. The behaviour of water droplets on a commercial polymer insulator exposed to AC voltage and their deformation on the surface is investigated experimentally [5]. The field distribution along the surface is numerically evaluated using Ansoft? 2D package (Figure 1). The results show the field distortion along the insulator surface due to the partially wet condition. The experiments are carried out to evaluate the electric field enhancement on the surface due to the droplets. Deformation and elongation of the water droplets have been observed and are reported (Figure 2).

A partial discharge measuring system has been used to detect corona from the tips of the droplets. The experiments, together with the field calculations, are helpful to understand the flashover mechanism of polymer insulation.

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G. F. Girda
Applied Electrostatics Research Centre
University of Western Ontario
London, ON Canada

Several different methods of liquid treatment using electric and magnetic fields are reviewed, focusing upon the use of high electric fields in coalescence of water droplets in water-in-oil emulsions and the use of permanent magnetic fields for scale removal in flowing water pipes. Electrocoalescence involves the use of high electric fields to produce the growth of water droplets in water-in-oil emulsions. The main factors that influence this process are discussed. In particular, results are described for an emulsion of water droplets in oil at concentrations of 0.9% and 4.5%. This emulsion is subjected to an intense electric field applied via insulated electrodes. The dependence of volume mean diameter as a function of exposure time to the applied electric field and as a function of peak applied voltage in the electrocoalescer are presented.

Considerable controversy exists regarding the use of permanent magnetic fields to remove scale in water pipes. One theory that could explain how the permanent magnetic field acts in order to stop and even remove the scale from the walls of pipes is presented, focusing on the main phenomena that take place in the water that contains calcium and magnesium components. An example of the scale removal by a magnetic field is shown for the treatment of a pipe after 3 and 6 months. The effect of the water velocity in the pipe upon the magnetic field treatment is also briefly discussed and how it is possible to reduce this dependency.

Despite the established use of magnetic water treatment and the obviously good results obtained, a generally accepted theory still does not exist. It remains to continue research in order to find one and to solve the main disadvantage of magnetic water treatment, the permanent presence of scale-causing substances in water.

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James Q. Feng
Xerox Corporation
Wilson Center for Research and Technology
800 Phillips Road
Webster, NY 14580, USA

Unipolar charge current can be generated through corona discharge from a thin wire enclosed in a shield electrode. Except for an ionization sheath adjacent to the coronating wire surface, most parts of the region in the enclosing shield contain drifting ions of a single polarity in response to the electric field. Momentum transfer as a consequence of collisions between drifting ions and electrically neutral air molecules gives rise to the electrohydrodynamic flow known as "corona wind." Although primarily driven by the Coulomb force due to unipolar charge in the electric field, the electrohydrodynamic flow cannot simply follow the direction of electric field lines because of the confinement of the solid walls of the shield. Therefore, the structure of the electrohydrodynamic flow can vary significantly depending on the system configuration. In the present work, the electrohydrodynamic flow in a rectangular shield is studied by solving the nonlinearly coupled governing equations via the Galerkin finite-element method. A highly symmetric system with the wire positioned at the center of a square shield is shown to contain eight equal-sized two-dimensional recirculation vortices. The number of recirculation vortices tends to be reduced by a slight asymmetry in the system. The flow structure of two major counter-rotating recirculation vortices is found to be most common in systems where the wire is positioned off the center of the rectangular shield in a two-dimensional domain. The results reported here may be brought to bear upon the "corona wind" effect in charging devices such as corotrons and scorotrons used in electrophotographic printing processes.

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Thomas V. Prevenslik

Consultant
11 F, Greenburg Court
Discovery Bay, Hong Kong

Over 100 years ago, Lenard explained waterfall electricity, a phenomenon described as the breakup of waterfall drops into fine particles that carry negative charge, the larger particles positive charges. Since then, waterfall electricity has been of interest to researchers, and is of special interest as this ESA Conference is held at Brock University near Niagara Falls, Ontario. Ion emission from waterfalls is proposed related to the phenomenon of sonoluminescence (SL). SL is usually described by the emission of visible (VIS) photons from bubbles in liquid , but is also known to dissociate molecules. It is therefore not unreasonable to postulate the source of ion emission from waterfalls to be and ions produced as bubbles nucleate in drops at the splash. In the Planck theory of SL, the source of SL is the electromagnetic radiation (EMR) at frequencies from the ultraviolet (UV) to soft X-rays where liquid is strongly absorptive (and emissive). The EMR is accessed in bubble nucleation by cavity quantum electrodynamics (QED) as frequencies less than the bubble EM resonant frequency are inhibited from the bubble. Since the bubble EM resonance at nucleation occurs at soft X-ray frequencies, the Planck energy of EMR from soft X-rays to the UV that existed before nucleation is inhibited from the space after nucleation. The inhibited EMR concentrates at the bubble wall and has sufficient Planck energy to dissociate the surface molecules into and ions. In this way, waterfall electricity is produced as the bubbles in the splash burst and the ions are discharged into the air. Consistent with the Lenard effect, the negative charge in the air near waterfalls, Niagara Falls in particular, is proposed to be ions that cluster with and molecules; whereas, the positive charge is the ions that cluster to molecules and remain near the splash.

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J. Ahern and W. Balachandran

Department of Systems Engineering
Brunel University
Uxbridge, Middlesex UB8 3PH, United Kingdom
email: empgjca@brunel.ac.uk

The splashing of water from a fountain, drips falling into a damp steel sink, or the slow emergence of drops of pure liquid during filtration, will sometimes give rise to small drops called boules, typically in the range 2-5 mm in diameter, which careen briefly on a cushion of vapour above the bulk liquid below, before being absorbed into it. The phenomenon has received relatively little attention, and has some interesting electrical events associated with it.

A brief review of the phenomenological literature is given. This is followed by a description of two methods by which boules may be produced in the laboratory with fair reliability. Finally, some experimental results are given. In the initial experiments the electric field-strength to inhibit the formation of boules was measured, and found to be in good conformity with that previously reported. This was followed by a series of measurements of the charge transferred by boules, and was found to be in the order of C for boules of some 3.5 mm diameter. The second series of experiments began the investigation of the electrical events associated with drop coalescence, with a view to possibly shedding some light on the mechanism of charge transfer in boules themselves. Work is continuing to gain a greater understanding of the mechanism of the charge transfer processes.

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Howard Tang, S. S. Chen, Scott Liu, M. T. Lee, C. H. Liu, M. C. Wang, and L. C. Hsia

Device Engineering
Dept. Technology and Process Development Division
United Microelectronics Corporation
No. 3, Li-Hsin Rd. 2, Science-Based Industrial Park
Hsin-Chu City, Taiwan, R. O. C
E-mail: howard_tang@umc.com.tw

In this paper, we will propose an ESD solution with cascode structure for deep-submicron IC technology to enhance its ESD robustness. Using the added boron implantation (PESD implantation) at the drain side of the stacked NMOS, the long-base parasitic NPN bipolar in the cascode NMOS structure can be easily triggered by the zener breakdown mechanism at the drain side under ESD stress conditions. Based on the test results, this method provides a significant improvement inthe cascode ESD performance.

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Peter P. Tsai¹, Heidi Schreuder-Gibson² and Phillip Gibson²

¹Textiles and Nonwovens Development Center (TANDEC)
  The University of Tennessee
  Knoxville, TN
  fax: (865) 974-3580, e-mail: ppytsai@utk.edu

²U. S. Army Soldier Systems Command
Natick Research, Development and Engineering Center

Fibrous materials used for filter media take the advantages of high filtration efficiency (FE) and low air resistance. Electrostatic charging of the media improves their FE by the electrostatic attraction of particles without the increase of pressure drop [1]. Three techniques, electrostatic spinning (ES) [2], corona charging [3] and tribocharging [4], are used to make and/or to charge the fibers or the fabrics. This paper will compare the FE and the surface charge potential of these three techniques. Their processes of making the media will be addressed and the media properties will be presented.

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Mark N. Horenstein¹, Seth Pappas, Asaf Fishov, and Thomas G. Bifano²

¹Department of Electrical and Computer Engineering

²Department of Manufacturing Engineering
  Boston University 44 Cummington St.
  Boston, MA 02215
  Tel: 617-353-9052 Fax: 617-353-6440
  Email: mnh@bu.edu

Wavefront sensors are used in many applications involving medical diagnostics, terrestrial imaging, target recognition, laser tracking, and astronomical observations. Under ideal conditions, the light emanating from a source image arrives as a series of uniform wave fronts that have the local structure of a plane wave at the image receiving device. In a practical situation, the latter could be a camera lens aperture, a photographic plate, the human eye, or a laser sensor. In situations where light from the image passes through a distorting medium, the light will no longer arrive as a local plane wave but rather as a non-planar, or "aberrated" wavefront. A wavefront sensor can help determine the degree of distortion in the aberrated wave. If the distorted wavefront is modeled as a series of connected, piecewise-linear planar wavefront segments, then the sensor can provide information about the degree to which the aberrated wavefront departs from an ideal plane wave.

Such a sensor is extremely useful in systems employing adaptive optics. In an adaptive optics (AO) system, information from the wavefront sensor is passed to an image correction device that typically includes one or more deformable mirrors. The latter act to redirect the incoming wave, sector by sector, until it regains the shape of an undistorted, regular plane wave. One traditional form of wavefront sensor is the commercially available Hartmann device, an array of tiny lenslets that each intercept one sector of the incoming wavefront. Each lenslet of a Hartmann device produces its own focused spot on the Hartmann image plane. If the incoming wave is regular and planar, the Hartmann sensor will produce an evenly spaced array of spots. If, on the other hand, the wavefront is distorted, then the spots produced by the Hartmann lenslets will be displaced from their normal positions. In an AO system, spot displacement can be detected by a charge-coupled imaging device (CCD), similar to what one would find inside a standard video camera.

A deformable mirror is a device whose reflected surface can be altered, sector by sector, to attain a slope that departs from its otherwise perfectly planar surface. In an adaptive optics system, the information derived from the Hartmann sensor is used to drive the elements of a deformable mirror placed in the optical pathway. The deformable mirror changes the direction of propagation each aberrant sector of the incoming image until the wavefront of the entire image again resembles a plane wave. The aberrant wavefront sectors are redirected to their proper directions, thereby "undistorting" the distorted image. One classic (non-electrostatic) example of a deformable mirror is the correction mirror that was placed inside the Hubble telescope approximately two years after its initial launch. This fixed, deformed mirror applies "reverse distortion" to the image reflected off of Hubble's flawed, primary mirror.

Unlike the large, fixed deformable mirror placed inside the Hubble, or likewise the "fun-house" mirrors that one finds in an amusement park, modern deformable mirrors are small (1 cm) and lightweight (grams), and are typically activated by electrostatic forces. They can be distorted at mechanical frequencies approaching 10 kHz. This feature makes possible real-time, electrostatic-activated image correction in situations where the distortion changes with time. Examples of the latter include terrestrial imaging through hot desert air, astronomical imaging through the earth's atmosphere, medical imaging through moving airways or blood vessels, and point-to-point laser communications through a smoke-filled environment. Real-time image correction with a conventional Hartmann sensor and deformable mirror requires complex digital signal processing. An analog-to-digital (A/D) converter must first digitize the pixel images from the CCD array. A dedicated computer or digital signal processing (DSP) chip must then decode the digitized data to determine the positions of the Hartmann spots, execute a control algorithm, and apply electrostatic correction signals via a digital-to-analog (D/A) converter and high-voltage amplifier to the elements of the deformable mirror. This process is computer intensive, electronics intensive, very time consuming., and often the factor most responsible for limiting process bandwidth in adaptive optics.

This paper proposes a novel way to perform sectored wavefront sensing without the use of a Hartmann sensor, a DSP chip, computer, or CCD. The Hartmann lenslet array is instead replaced with a binary-actuated, electrostatic digital-mirror device (DMD) and a single, position-sensitive spot detector. The CCD, analog-to-digital converter, and computer are replaced with a simple, robust, analog electronic circuit and high-voltage amplifier made from simple, off-the-shelf parts. With these components alone, sectored wavefront sensing can be performed without any digital image processing or Hartmann device. The segments of a correcting deformable mirror can instead be controlled directly from the output of the position-sensitive spot detector.

This paper also discusses the features of the binary-mode electrostatic digital mirror device (DMD) used in our experiments. The DMD is an array of electrostatically-actuated micro-mirrors each capable of being driven into one of two positions, or bistable states. Unlike the sectors of a deformable mirror, which are a continuously variable, analog devices, the pixels of the DMD can reflect light in one of two preset directions only. The DMD is made using low-temperature, micro-electromechanical (MEMS) fabrication technology. The physics and fabrications methods of the digital mirror device elements are discussed in detail.

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P. O. Grimaud and G. Touchard

LEA, UMR 6609
Equipe Electrofluidodynamique
Boulevard Marie et Pierre Curie,
Teleport 2, BP 30179
86962 Futuroscope-Chasseneuil, France

Phenomenon of self-potential is nowadays of greater and greater interest in geophysics as it finds utility in various environmental fields such as evaluation of volcanic and seismic risks or hydrorheology. It is well known that motion of fluid inside a porous medium generates creation of streaming potentials.

Considering a porous medium inside of which a fluid is moving, number of studies have shown correlations between streaming potential and various parameters characteristic of the medium, but it always seems to be independent of the temperature of the medium.

However, explanation of this last observation never has been well explained. This is the reason why the aim of our work first consists to show theoretically the non-dependence of streaming potential with temperature, then to confirm it with an experimental study.

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