Abstract: A method for depositing a substance on a substrate that involves forming a supercritical fluid solution of at least one supercritical fluid solvent and at least one solute, discharging the supercritical fluid solution through an orifice under conditions sufficient to form solid particles of the solute that are substantially free of the supercritical fluid solvent, and electrostatically depositing the solid solute particles onto the substrate. The solid solute particles may be charged to a first electric potential and then deposited onto the substrate to form a film. The solute particles may have a mean particle size of less than 1 micron.

Abstract: A method for forming a continuous film on a substrate surface that involves depositing particles onto a substrate surface and contacting the particle-deposited substrate surface with a supercritical fluid under conditions sufficient for forming a continuous film from the deposited particles. The particles may have a mean particle size of less 1 micron. The method may be performed by providing a pressure vessel that can contain a compressible fluid. A particle-deposited substrate is provided in the pressure vessel and the compressible fluid is maintained at a supercritical or sub-critical state sufficient for forming a film from the deposited particles. The Tg of particles may be reduced by subjecting the particles to the methods detailed in the present disclosure.

Abstract: An electrospraying apparatus and/or method is used to coat particles. For example, a flow including at least one liquid suspension may be provided through at least one opening at a spray dispenser end. The flow includes at least particles and a coating material. A spray of microdroplets suspending at least the particles is established forward of the spray dispenser end by creating a nonuniform electrical field between the spray dispenser end and an electrode electrically isolated therefrom. The particles are coated with at least a portion of the coating material as the microdroplet evaporates. For example, the suspension may include biological material particles.

Abstract: A feedback control system for an electrospray nozzle and counter-electrode, comprising a source of light which intersects, one or snore of the liquid cone, jet and plume of the fluid exiting the nozzle, one or more photo detectors to detect light patterns and generate photo-electronic signals in response thereto, an electronic detection and amplification system to convert the photo-electronic signals to electronic signals, a computer or micro-processor to interpret said electronic signals and a second computer or microprocessor to communicate with the first computer and generate a signal to a controller which adjusts the electric field surrounding the nozzle either by changing the distance between the nozzle and counter-electrode or changing the voltage of the nozzle or counter-electrode.

Abstract: A method for determining a layer thickness distribution in a paint layer produced during paint spraying after inputting specific spraying parameters into an electrostatically based paint spraying device. A data processing device sets up and uses a phenomenological mathematical model of a quasi-stationary three-dimensional spray pattern. Specific parameters, such as an angle of rotation of electrodes and a rate of movement of the spraying device are input into the phenomenological model as fixed input parameters. In addition, real physical input parameters such as paint volume, directing air data and a voltage value, whose influence on the spraying result is not accurately known, are fed to an artificial neural network. The neural network having been previously trained using real input data such as a configuration of the spraying device, a paint type, operating parameters, and measured values of the layer thickness distribution.

Abstract: An apparatus and method are disclosed for efficiently applying a test substance to a test unit by atomizing a solution or suspension of the test substance and electrostatically attracting the atomized droplets to the test unit. This apparatus and method can be used to apply small quantities of test substances to organisms such as plants or insects to assay their utility as crop protection agents.

Abstract: A method and apparatus to improve the atomization of liquid and the efficiency of depositing liquid particles onto target objects, or to coat the target object with a thin film of liquid, to reduce the risk of high-voltage electrical shock, and to reduce the weight of an electrostatic spray system has been developed by inducing electrostatic charges onto the atomized liquid particles sprayed from a grounded metal nozzle.

Abstract: An improved method for charging ultrafine particles in coronas (e.g., unipolar or bipolar corona discharges) by exposing the particles to X-ray irradiation. Experimental tests have verified that positive corona in the presence of X-ray irradiation results in maximum or optimum charging efficiency, followed by a negative corona in the presence of X-ray irradiation, X-ray radiation only (without corona), negative corona only (without X-ray irradiation), and finally positive corona only (without X-ray irradiation). This method and system is particularly well suited for use with bioaerosol particles wherein exposure to the corona discharge and X-ray irradiation serves to both capture and inactivate the bioaerosol particles using a single device.

Abstract: An apparatus and method for fluid emission control of a conductive fluid utilizes a passive electrolytic reaction to ionize the conductive fluid. The apparatus includes a fluid emission system having a reaction chamber that includes an anode and cathode to initiate an electrolytic reaction within the conductive fluid and reaction chamber. An ion-generating member is disposed within the reaction chamber and enhances the electrical bias in the conductive fluid. An oxidation-controlling member disposed within the reaction chamber retards oxidation of the anode and cathode. The metallic component parts and amount of such component parts used in the reaction chamber are chosen to achieve a target voltage, which that amount of voltage created, by the electrolytic reaction necessary to charge a fluid droplet of any density to achieve a maximum acceleration of fluid droplets as the fluid droplets enter and leave a spray cone.

Abstract: An atomizing spray nozzle structure comprising a main unit, a rotor and a spray nozzle, wherein the main unit and the spray nozzle are joined by thread tightening. Inside the main unit is an accommodating space. The spray nozzle has a through channel running along the axis thereof. The accommodating space is communicative with the through channel, having a rotor inside the through channel and the accommodating space, characterized in that: the rotor has a length longer than the through channel at all circumstances, with one end exposed in the accommodating space of the main unit; thereby the rotor can be easily taken out for cleaning purpose after the main unit and the spray nozzle are disassembled.

Abstract: A method for forming a continuous film on a substrate surface that involves depositing particles onto a substrate surface and contacting the particle-deposited substrate surface with a supercritical fluid under conditions sufficient for forming a continuous film from the deposited particles. The particles may have a mean particle size of less 1 micron. The method may be performed by providing a pressure vessel that can contain a compressible fluid. A particle-deposited substrate is provided in the pressure vessel and the compressible fluid is maintained at a supercritical or sub-critical state sufficient for forming a film from the deposited particles. The Tg of particles may be reduced by subjecting the particles to the methods detailed in the present disclosure.

Abstract: A method for depositing a substance on a substrate that involves forming a supercritical fluid solution of at least one supercritical fluid solvent and at least one solute, discharging the supercritical fluid solution through an orifice under conditions sufficient to form solid particles of the solute that are substantially free of the supercritical fluid solvent, and electrostatically depositing the solid solute particles onto the substrate. The solid solute particles may be charged to a first electric potential and then deposited onto the substrate to form a film. The solute particles may have a mean particle size of less than 1 micron.

Abstract: A method for depositing a substance on a substrate that involves forming a supercritical fluid solution of at least one supercritical fluid solvent and at least one solute, discharging the supercritical fluid solution through an orifice under conditions sufficient to form solid particles of the solute that are substantially free of the supercritical fluid solvent, and electrostatically depositing the solid solute particles onto the substrate. The solid solute particles may be charged to a first electric potential and then deposited onto the substrate to form a film. The solute particles may have a mean particle size of less than 1 micron.

Abstract: In a gas inlet structure for an ion source, including a capillary for the admission of a sample gas, which capillary is disposed in a guide tube for discharging a sample gas into the guide tube, the guide tube has an open end disposed in the ion source. The guide tube includes a valve for the pulsed admission of a carrier gas to the guide tube. The guide tube, the valve and the capillary are supported in a sealed support housing from which the guide tube with the capillary disposed therein projects into the ion source for supplying thereto the sample gas in a pulsed manner.

Abstract: A method of improving the spraying of liquid droplets from a spray device onto a surface which method comprises imparting a unipolar charge to the said liquid droplets by double layer charging during the spraying of the liquid droplets from the spray device, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at least ±1×10−4 C/kg, whereby the charged droplets of the liquid are mutually repelled thereby increasing the spread of the droplets from a central spray line extending from the head of the spray device and avoiding coalescence of the droplets, thus providing a more even coverage of the surface which is to be sprayed. In particular, the method enables liquid droplets to be sprayed onto a surface which is obscured by all object located between the surface and the spray device.

Abstract: An apparatus for dispersing a fluent material has an initial disperser for breaking a stream of fluent material into discontinuous parts. The apparatus has an electrode supply device that provides free electrons that impart a net charge on the discontinuous parts to disperse the discontinuous parts. A method is also disclosed in which electrons are directed at a flow of droplets of fluent material to disperse the fluent material.

Abstract: A flow sensor for use in a harvester is disclosed. The flow sensor has a microwave transceiver for transmitting a microwave signal and receiving a reflected microwave signal, an in-phase mixer electrically connected to the microwave transceiver for combining the transmitted microwave signal and the reflected microwave signal and outputting an in-phase Doppler signal, a quadrature mixer electrically connected to the microwave transceiver for combining the transmitted microwave signal and a delayed reflected microwave signal and outputting the quadrature Doppler signal, and an electronic circuit electrically connected to the in-phase mixer and the quadrature mixer and having a flow rate output.

Abstract: A method for fixing a first fluid within a second fluid which includes the steps of mixing the first and second fluids together and subjecting the first and second fluids to an electric field and a high voltage corona like electric discharge. The method can be used, for example, to increase the oxygen content of water. It can also be used for the treatment of waste effluent. An apparatus for carrying out the process includes a fluid passageway defined between inner and outer elongated conduits with a preferably spirally configurated baffle means in the passageway and a plurality of electrode needles extending into the passageway.

Abstract: An improved method of counteracting or neutralizing airborne malodour comprising directing at the source of the malodour liquid droplets from a spray device containing a malodour counteracting composition, the improved method comprising imparting a unipolar charge to the said liquid droplets by double layer charging during the spraying of the liquid droplets by the spray device, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at least ±1×10−4C/kg.

Abstract: An electrostatic atomizer includes a body defining an interior space and a discharge orifice communicating with the interior space. An emitting electrode or electron gun is disposed inside the body so as to apply charges to the fluid passing through the interior space. A counter electrode is disposed outside the body. The exposed surfaces on the interior of the body are formed from a dielectric material so that there is no substantial electric field between exposed conductive elements on the inside of the body. This arrangement minimizes soot buildup and plugging of the orifice. The device may include a single element defining numerous orifices and formed by micro-machining techniques such as those used in fabrication of semiconductor devices. Orifice sizes as small as a few micrometers can use successfully to provide controllable atomization at extremely low flow rates.

Abstract: An improved method of denaturing or deactivating an airborne allergen comprising directing at the airborne source of the allergen liquid droplets from a spray device containing a liquid composition which includes an allergen denaturant or allergen deactivant, the improved method comprising imparting a unipolar charge to the said liquid droplets by double layer charging during the spraying of the liquid droplets by the spray device, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at leaset ±1×10−4 C/kg.

Abstract: A spraying device for dispensing electrostatic liquid droplets includes a container holding a liquid at one end, and having a nozzle assembly with an aperture at another end. The nozzle assembly includes a longitudinal hollow tube terminating in a metallic structure. The metallic structure includes a metallic base plate having at least one aperture formed therein for fluid communication with the hollow tube. The longitudinal hollow tube includes an end inserted in the liquid. A charge accumulator disposed in the liquid accumulates electrostatic charges. A wire conductor between the base plate and the charge accumulator transfers the electrostatic charges from the liquid to the nozzle assembly.

Abstract: An electrospray device, a liquid chromatography device and an electrospray-liquid chromatography system are disclosed. The electrospray device comprises a substrate defining a channel between an entrance orifice on an injection surface and an exit orifice on an ejection surface, a nozzle defined by a portion recessed from the ejection surface surrounding the exit orifice, and an electrode for application of an electric potential to the substrate to optimize and generate an electrospray; and, optionally, additional electrode(s) to further modify the electrospray.

Abstract: A electrohydrodynamic aerosol sprayer wherein a gas flow deflector is used for creating a gas flow past the spray nozzle to stabilize the Taylor cone and to transport at least a portion of the aerosol away from the region downstream of the spray nozzle. This stabilization of the cone and transport of aerosol improves the droplet size and distribution and may also reduce the deposit of droplets on the internal components of the device.

Abstract: A method and a configuration are provided for transporting electrically conductive paint from a point at earth potential to at least one paint application device which is at a high voltage potential. A needed quantity of paint is filled into a cartridge at a point at earth potential. The filled cartridge is conveyed by a first conveying device to a second conveying device. The cartridges are then allocated to workpieces to be painted. The filled cartridge is transported by the second conveying device to the at least one paint application device. At the paint application device, the cartridge is connected to at least one spray head. The emptied cartridge is transported by the second conveying device to a third conveying device, and the third conveying device transports the cartridge back to the loading station, while a further cartridge is filled there and conveyed by the first conveying device.

Abstract: This invention relates to an inhalation apparatus for dispensing an inhalable substance and, in particular, but not exclusively, to an apparatus for use in the delivery of therapeutic substances to the human lung. There is provided and apparatus for dispensing an aerosol of electrostatically charged droplets including a housing having an open end duct in which are located a first electrode having an upper surface lying in a generally longitudinal plane of the duct and a second electrode spaced from the first electrode. The apparatus further includes means for delivering a metered quantity of liquid to the upper surface of the first electrode for atomization, and charging means for applying a higher potential to the second electrode with respect to the first electrode to effect atomization.

Abstract: A solder jet apparatus is disclosed The solder jet apparatus is a continuous mode solder jet that includes a blanking system and raster scan system. The use of the raster scan and blanking systems allows for a continuous stream of solder to be placed anywhere on the surface in any desired X-Y plane. This allows for greater accuracy as well as greater product throughput. Additionally, with the raster scan system, repairs to existing soldered surfaces can be quickly and easily performed using a map of the defects for directing the solder to the defects.

Abstract: A spraying device for dispensing electrostatic liquid droplets includes a container holding a liquid at one end, and having a nozzle assembly with an aperture at another end. The nozzle assembly includes a longitudinal hollow tube terminating in a metallic structure. The metallic structure includes a metallic base plate having at least one aperture formed therein for fluid communication with the hollow tube. The longitudinal hollow tube includes an end inserted in the liquid. A charge accumulator disposed in the liquid accumulates electrostatic charges. A wire conductor between the base plate and the charge accumulator transfers the electrostatic charges from the liquid to the nozzle assembly.

Abstract: The present invention relates to methods and apparatus that employ electrohydrodynamic flows in miscible, partially miscible and immiscible multiphase systems to induce mixing for dissolution and/or reaction processes.

Abstract: A comminuting liquid device, a medicament delivery device, an inhaler, a method of providing droplets for delivery to the respiratory tract, a pocket-sized dispenser, and a method of mixing liquids by droplet coalescence. Liquids are subjected to electrical potentials to produce electrically charged droplets for delivery to the upper respiratory tract.

Abstract: The invention provides an aerosol delivery method and system for producing a charged electrohydrodynamic (EHD) aerosol, discharging the aerosol and moving the discharged aerosol in a desired direction without substantial wetting of the device. The delivery system may include a spray nozzle for dispensing the fluid to be aerosolized and negatively charging the aerosol droplets, a discharge electrode generally downstream of the spray nozzle for generating a positive ion stream which intercepts and electrically neutralizes the negative aerosol droplets while also imparting a desired movement on the aerosol in a direction generally away from the discharge electrode and a reference electrode between the spray nozzle and the discharge electrode for modifying the electric field between the spray nozzle and the discharge electrode.

Abstract: A paint spray system for directing paint to a part has a paint atomizer head having a bell housing and a bell-atomizer. An electrically conductive tape is applied to a surface of the paint atomizer. The tape may be applied to the bell housing or the front surface or side surfaces of the support housing. Tape is electrically connected to a power source to generate an electrical field and thereby an electrical force on charged paint particles produced at bell-atomizer. The electrical field repels the paint particles from the paint atomizer head to reduce the maintenance of the paint spray system.

Abstract: A method of reducing the droplet sizes of a composition sprayed from an aerosol spray device comprising a compressed gas propellant, which method comprises imparting a unipolar charge to the liquid droplets by double layer charging during the spraying of the liquid droplets from the aerosol spray device, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at least +/−1×10−4 C/kg.

Abstract: A dispensing device and method for forming a least partially solid or gel-like material from a liquid. At least one liquid issuing from an outlet is subjected to an electric field causing the liquid to form at least one electrically charged jet which, after formation, forms a fiber (F) or breaks up into fiber fragments (FF) or particles (D). The thus formed at least partially solid or gel-like material may be directly deposited, by virtue of the energy in the electrical field, onto a surface area, for example an area of skin enabling, for example, formation of a dressing for a wound or burn which is of high specific area and extremely absorbent. A biologically active ingredient such as a pharmaceutical ingredient or biological matter such as DNA may be incorporated into the fibers (F), fragments (FF) or particles (D). Fibrils, particles or microcapsules incorporating a biologically active ingredient may be supplied for oral or nasal administration to an animal such as a human being.

Abstract: An electrospray device, a liquid chromatography device and an electrosprayliquid chromatography system are disclosed. The electrospray device comprises a substrate defining a channel between an entrance orifice on an injection surface and an exit orifice on an ejection surface, a nozzle defined by a portion recessed from the ejection surface surrounding the exit orifice, and an electrode for application of an electric potential to the substrate to optimize and generate an electrospray; and, optionally, additional electrode(s) to further modify the electrospray.

Abstract: A method of killing flying insects which method comprises spraying into the air in which insects are flying liquid droplets of an insecticidal composition, a unipolar charge being imparted to the said liquid droplets by double layer charging and charge separation during spraying, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at least +/−1×10−4 C/kg.

Abstract: An electrostatic spray module for applying agricultural liquids such as a pesticide to crops where, externally to the spray module the number of connections is reduced to three, one for the liquid pesticide, one for compressed air and one for a low voltage signal. Internally to the spray module, the low voltage is converted to a high voltage signal, which is, along with the pesticide and the compressed air delivered to one or more electrostatic spray nozzles using only two electrically conductive pipes, a gas delivery pipe and a liquid delivery pipe. The nozzles fit into the gas delivery pipe and draw the compressed air through gas channel openings in the side of the nozzles. The gas delivery pipe doubles as the means to delivery the high voltage signal to the nozzles. Each nozzle has a liquid feed from the liquid delivery pipe, which carries ground voltage, maintaining the liquid at ground voltage. The grounded liquid merges with the compressed air in the nozzles to form an atomized liquid.

Abstract: A non-contact electrostatic liquid dispensing system and method for dispensing continuous, high viscosity viscoelastic nonconductive liquid strands in a controlled manner onto a substrate. An applicator or gun having a charging electrode introduces an electrostatic charge to the high viscosity viscoelastic nonconductive liquid and as charged continuous fibrous strand of high viscosity viscoelastic nonconductive material. One or more electric fields are generated about the discharge path to impart a variety of movements or patterns to the charged continuous fibrous strand of high viscosity viscoelastic nonconductive liquid.

Abstract: A device for comminuting liquid has a liquid supply with first and second outlets, a first electrohydrodynamic comminuter for subjecting liquid issuing from the first outlet to an electrical potential to cause the liquid to be commrinuted to form a comminution of one polarity and a second electrohydrodynamic comminuter for subjecting liquid issuing from the second outlet to an electrical potential to cause liquid to be commninuted to form a comminution of the opposite polarity. The first and second electrohydrodynamic comminuters are arranged so as to cause substantial admixing of two opposite polarity comminutions.

Abstract: A powder spray gun, and method for using same, is disclosed. The powder gun includes a corona discharge tip and mesh screen within the passage for powder flow. A potential is applied to the corona discharge tip, resulting in an electric field between the corona discharge tip and mesh screen. This electric field efficiently charges powder particles passing through the spray gun, but the mesh screen blocks most of the free ions that are generated by the corona discharge tip. Any free ions that pass through the mesh screen are captured by a conductive end piece on the spray gun. A potential difference is applied between the end of the spray gun and the workpiece to guide the charged powder particles to the workpiece.

Abstract: An electrostatic spraying device is disclosed which is suitable for, but not limited to, dispensing an electrostatically sprayable substance for nasal or oral inhalation. Electrical charge is imparted to the spray particles by applying a high voltage to the substance prior to break up into a spray. In one embodiment, the device includes a nozzle portion for registry with the nasal or oral cavity and defines a passageway through which, in use, air can be drawn by inhalation on the part of the user. The substance to be sprayed passes into the passageway so that, with the assistance of user-induced air flow through the passageway, the resulting spray passes into the oral or nasal cavity.

Abstract: A device for dispensing a comminuted liquid to the upper respiratory tract, which comprises an electrohydrodynamic comminution device and a supplier of a liquid to the comminution device. And a device for comminuting a liquid, the comminution site of which is provided by fibers projecting from an end surface or edge, the edge or surface being composed substantially of fibers.

Abstract: A process and a dispersion apparatus for shaping a powder cloud emerging from a powder spraying apparatus achieve large powder clouds and good electrostatic charging by directing control air in a tangential direction towards a powder/air stream flowing through the dispersion apparatus in an axial spraying direction. A helically accelerated movement of the powder/air stream in the direction of an outlet is achieved thereby.

Abstract: Apparatus for powder spray coating comprises means for electrostatically-charging powder entrained in air, a conduit for transporting the electrostatically charged powder from the charging means to a spray head adapted to discharge the powder in a hollow conical spray pattern, wherein the spray head comprises means for diverting at least a portion of the flow of charged powder towards a spray device mounted to the spray head and adapted to discharge powder in a substantially uniform conical spray pattern, the spray head, spray device and the hollow conical and conical spray patterns being substantially symmetrical about a common longitudinal axis. The apparatus is particularly suitable for coating a large surface area. Preferably multiple tribo-electric charging means are used and a pump is used to supply powder to the multiple charging means through a common distributor. After passing through the multiple charging means the powder flows are then recombined and sprayed through a common spray apparatus.

Abstract: Workpieces are electrostatically coated with powder materials. It is possible to attain a relatively large coating thickness in a single operation by simultaneously or alternately coating with powder particles that have a different electrical charge. The process can be used in applying single-component or multi-component coating materials.

Abstract: An apparatus for reducing undesirable powder accumulation on an electrostatic powder coating device is provided. The apparatus includes a pneumatic source for generating a pneumatic supply. The pneumatic supply is received and distributed by a pneumatic distribution device which provides the pneumatic supply to a pneumatic diffuser. The pneumatic diffuser directs a pneumatic stream at the electrostatic coating device such that undesirable powder accumulation on the electrostatic powder coating device is reduced.

Abstract: A spray gun for applying powder to coat a work piece uses triboelectric and optionally a corona discharge electrode to charge powder particles electrostatically. The gun communicates with a source of pressurized air through a handle with an air valve controlling flow of the air. Powder in a container in fluid communication with the air flow is fluidized and entrained when the valve is opened. A nozzle with an internal surface defining a passageway to an open end communicates with the powder container. The internal surface of the nozzle frictionally imparts a net electrical charge of a first polarity to part of the powder by frictional contact during spraying. A plurality of discrete tubes are disposed in the central passageway and impart a net electrical charge of a second polarity to another part of the powder due to frictional contact as that part flows around and through the tubes.

Abstract: Conductive, flowable, emollient compositions and electrostatic methods for their application e.g., to tissue, are disclosed. Compositions of the invention include emollient(s) and conductivity modifiers. Emollient-compatible phosphates and succinates are particularly preferred families of conductivity modifiers. In methods of the invention conductive emollient composition of the invention are preferably applied to tissue substrates, particularly facial tissue substrates, and particularly in a commercial tissue-making process. Electrostatic spray processes are utilized to obtain surprisingly uniform application of conductive emollient to tissue with minimal overspray or spray path overlap.

Abstract: An apparatus and method are disclosed for the aerial spraying of agricultural chemicals with improved spray deposition and reduced drift. The spraying apparatus includes two oppositely charged sets of spray nozzles which may be fitted onto an aircraft. Both sets include one or more nozzles having spraying tips which produce a hollow cone spray pattern, and at least the tips of these nozzles are constructed of a substantially non-conducting material. Cylindrical electrodes are positioned concentric to the nozzle tips for inducing an electrostatic charge upon liquid spray emitted from the nozzles. The electrodes are in turn connected to high voltage power supplies, with the electrodes corresponding to the first nozzle set being connected to a power supply of opposite potential than the electrodes corresponding the second nozzle set. Consequently, the spray issuing from the nozzle sets will be oppositely charged.

Abstract: An electrostatic, liquid spray, rotary atomizer has an atomizer housing, a power supply within the housing and an atomizer cup at a front end of the housing. The atomizer cup, which is formed of a non-conductive material, has several elongate conductive pathways embedded in the body of the cup. Each conductive pathway has one end exiting an outer surface at a rear end of the cup for receiving the charge from the power supply and another end exiting an inner surface at a front end of the cup for conveying an electrical charge from the power supply to the liquid (paint) particles passing through the atomizer cup. An electrode is provided for maintaining a small voltage at the access hole.