Abstract: A failure indicator seal includes a nonmagnetic housing, a plurality of annular pole pieces having distal ends, the plurality of annular pole pieces disposed within the nonmagnetic housing, an annular, non-conducting magnet disposed between the pole pieces, a predefined quantity of magnetic fluid disposed between each of the distal ends of the plurality of annular pole pieces and the rotary shaft of a rotary feedthrough forming a plurality of magnetic fluid O-ring seals, and means for measuring resistance through the plurality of annular pole pieces, the plurality of magnetic fluid O-ring seals and the rotary shaft.

Abstract: A failure indicator seal includes a nonmagnetic housing, a plurality of annular pole pieces having distal ends, the plurality of annular pole pieces disposed within the nonmagnetic housing, an annular, non-conducting magnet disposed between the pole pieces, a predefined quantity of magnetic fluid disposed between each of the distal ends of the plurality of annular pole pieces and the rotary shaft of a rotary feedthrough forming a plurality of magnetic fluid O-ring seals, and means for measuring resistance through the plurality of annular pole pieces, the plurality of magnetic fluid O-ring seals and the rotary shaft.

Abstract: A ferrofluid seal apparatus incorporating a multi-stage ferrofluid rotary seal adapted to provide a ferrofluid pressure-type seal about a shaft element extending between a first environment and a second environment, a first magnetic fluid disposed at one stage of the multi-stage rotary seal that faces the first environment, and a second magnetic fluid disposed at another stage of the multi-stage rotary seal that faces the second environment.

Abstract: A ferrofluid seal apparatus incorporating a multi-stage ferrofluid rotary seal adapted to provide a ferrofluid pressure-type seal about a shaft element extending between a first environment and a second environment, a first magnetic fluid disposed at one stage of the multi-stage rotary seal that faces the first environment, and a second magnetic fluid disposed at another stage of the multi-stage rotary seal that faces the second environment.

Abstract: Magnetic fluid seals containing housings, magnets, pole pieces, gaps, magnetic fluids, shafts and bearings of standard type are modified to permit operation at two levels of magnetic intensity in the gaps. During exposure to the operating pressure difference that a seal is designed to withhold, the magnetic field intensity in the gaps is maintained at a relatively low intensity. Subsequently, the magnetic field intensity in the gaps is increased to yield burst-free operation. Various embodiments for adjusting the magnetic field intensity are disclosed. These include: magnetic fluid seal with a variable magnet to pole-block spacing; seal with hollow-shaft flux intensifier; seal with surrounding flux diverter; and seal with an internal magnetic coil that furnishes opposing magnetomotive force.

Abstract: Magnetic sculptures are formed by placing a ferrofluid in a shaped magnetic field. In response to the field, the ferrofluid forms fanciful sculptures as determined by the magnetic field lines. In one embodiment, a low viscosity and surface tension ferrofluid is used in a sealed housing to prevent the ferrofluid from evaporating. The housing is filled with a nonmagnetic liquid that is immiscible with the ferrofluid and contains a ferrofluid globule. In order to prevent the ferrofluid from wetting the inside surface of the housing and degrading the apparatus, the housing is comprised of a boro-silicate glass and the ferrofluid comprises a fluorocarbon carrier liquid. Magnetic sculptures can be formed by applying an external magnetic field of sufficient strength to the apparatus. In another embodiment, the aforementioned apparatus may contain a small permanent magnetic located within the ferrofluid globule.

Abstract: Ferrofluid coated particles resulting from a ferrofluid materials separation process are washed with a solvent which is the same material as the liquid carrier employed in the ferrofluid. The result is a “dirty” solvent which is a very weak ferrofluid. The dirty solvent is then filtered or centrifuged to remove dust particles and other impurities and then the solvent is recovered by distillation in a distillation unit. The solvent can then be reused in the materials reclamation process. The residue in the distillation unit is surfactant-coated particles of ferrofluid. This residue is mixed with either clean or unprocessed solvent in the right proportion and the slurry is passed through an attritor to convert it to a high grade ferrofluid. The ferrofluid can also be reused in the materials separation process.

Abstract: Ferrofluid coated particles resulting from a ferrofluid materials separation process are washed with a solvent which is the same material as the liquid carrier employed in the ferrofluid. The result is a "dirty" solvent which is a very weak ferrofluid. The dirty solvent is then filtered or centrifuged to remove dust particles and other impurities and then the solvent is recovered by distillation in a distillation unit. The solvent can then be reused in the materials reclamation process. The residue in the distillation unit is surfactant-coated particles of ferrofluid. This residue is mixed with either clean or unprocessed solvent in the right proportion and the slurry is passed through an attritor to convert it to a high grade ferrofluid. The ferrofluid can also be reused in the materials separation process.

Abstract: A slurry is formed of particles of a non-magnetic oxide of iron (.alpha.-Fe.sub.2 O.sub.3), an oil carrier liquid and a surfactant. The slurry is then processed in an attrition mill where kinetic energy is applied to the slurry to convert the .alpha.-Fe.sub.2 O.sub.3 particles to magnetic iron oxide particles to form an oil-based ferrofluid. In order to increase the saturation magnetization of the resulting ferrofluid, a beneficial agent is brought into contact with the slurry during processing in the attrition mill. The beneficial agent can be a magnetic material, such as elemental iron, or can be water. A ferrofluid can also be formed by creating a powder of surfactant-coated magnetic particles and using an attrition mill to coat the particles with a second surfactant and suspend the coated particles in a carrier liquid.

Abstract: A solenoid includes a ferrofluid in gaps between the moving and stationary elements which ferrofluid reduces noise caused by activating a plunger positioned within the solenoid. A permanent magnet can be included as a solenoid element to increase magnetic field strength within the solenoid to retain the ferrofluid within the solenoid.

Abstract: A ferrofluid manufacturing process applies energy to a nonmagnetic .alpha.-Fe.sub.2 O.sub.3 starting material to render it magnetic and suitable for use in a ferrofluid. The material is placed, together with a solvent and a surfactant, in a commercial attrition mill where the mill action converts the non-magnetic particles to magnetic particles. In order to eliminate a solvent replacement step which is necessary with oil carrier liquids, water is used as the grinding solvent and as the ferrofluid carrier liquid. The resulting water-based ferrofluid has a high saturation magnetization, low viscosity and good colloidal stability. Using the inventive method, a large volume of fluid can inexpensively be synthesized in a short time.

Abstract: A solenoid includes a ferrofluid in gaps between the moving and stationary elements which ferrofluid reduces noise caused by activating a plunger positioned within the solenoid. A permanent magnet can be included as a solenoid element to increase magnetic field strength within the solenoid to retain the ferrofluid within the solenoid. A cushion located between the plunger and a butt toward which it moves also reduces the noise, while the ferrofluid maintains a relatively high solenoid force relative to a solenoid with air gaps.

Abstract: A ferrofluid sensor assembly includes a closed housing containing a movable inductance core material that is isolated from the inner walls of the housing by an isolating material. The isolating material forms a layer between the inductance core material and the walls of the housing to prevent their contact. A detector also is included for detecting the position of the inductance core material within the housing.

Abstract: A ferrofluid composition comprising a colloidal dispersion of finely divided magnetic particles in a silicone oil carrier in which the surfaces of the magnetic particles are modified with (a) a first surfactant comprising a hydrocarbon having at least one polar group and (b) a second surfactant comprising a silicone oil surfactant having at least one polar group and which is soluble in the silicone oil carrier.

Abstract: A ferrofluid sensor assembly includes a permanent magnet which is supported in a hermetically-sealed housing by ferrofluid rings at each end of the magnet. However, the housing is large enough that the ferrofluid rings do not seal the end of the magnet against the walls of the housing. The housing is filled with a non-magnetic liquid that is immiscible with the ferrofluid. The nonmagnetic liquid wets the walls of the housing such that the ferrofluid rides on the thin film of the nonmagnetic liquid. The non-magnetic fluid is selected to have low viscosity, so that the magnet has a fast response time.

Abstract: A liquid level monitoring system, which monitors the level of liquid in a storage tank, includes a differential pressure sensor that uses a magnetic fluid, or ferrofluid, sensing element. The pressure sensor is U-shaped with a first one leg connected, via a first pressure chamber, to a bubbler tube that extends downwardly into the storage tank. The second leg of the U-shaped sensor connects to a second pressure chamber, which applies to the second leg a selected, fixed pressure. The pressure applied to the first leg of the sensor is proportional to the hydrostatic back pressure in the bubbler tube, which varies directly with the level of liquid in the storage tank. Wound around the legs of the pressure sensor are inductance coils. The inductances of these coils change as the ferrofluid sensing element moves within the sensor. Accordingly, the inductances change as the level of liquid in the storage tank varies.

Abstract: Mechanically simple, reliable devices for measuring pressure or detecting pressures above a certain limit are disclosed. A representative device includes a magnet surrounded by one or more bands of a ferrofluid, and which is free to move within a nonmagnetic, generally elongated housing. In operation, the housing is oriented vertically, and the lower aperture exposed to the region of pressure to be sensed. The opposite end, which preferably contains another aperture, is exposed to a reference pressure (ordinarily the atmosphere) that remains isolated from the region of pressure to be sensed. Gravity draws the magnet downward, toward the bottom of the housing, while pressure at the lower aperture tends to force the magnet upward. When the force exerted by the pressure source exceeds the downward force of gravity, the magnet travels upward through the housing; this movement may be detected by an appropriate sensing arrangement, and is used to provide a warning signal or a quantitative pressure measurement.

Abstract: A convection-cooled electromagnetic device, such as a transformer, and methods of cooling that utilize a ferrofluid as a cooling medium. The device's leakage magnetic field, which can be augmented by auxiliary magnets, draws the ferrofluid toward the device. As the fluid approaches the device its temperature rises, resulting in loss of magnetic properties and a decrease in density. The ferrofluid rises as its temperature approaches the Curie point, since the gravitational effect of density reduction begins to overcome the weakening magnetic attraction. Movement of hot ferrofluid is strongly assisted by the attraction exerted by the device on cooler, more intensely magnetic ferrofluid, which displaces the hot ferrofluid. The displaced ferrofluid cools as a result of movement from the heat source and through contact with the walls of the housing. Preferably, the Curie temperature of the ferrofluid is close to or slightly higher than the operating temperature of the device.

Abstract: A loudspeaker including one or more secondary magnets positioned proximate to an opening of a gap through which a voice coil moves, to capture escaping ferrofluid and return the fluid to the gap. The secondary magnets have axial poles and are oriented, relative to a speaker magnet, to enhance the radial magnetic flux within the gap and to diminish the flux of a fringe field axially adjacent to the gap. When ferrofluid escapes from the gap, it is captured and held by one of the secondary magnets at a distal edge, which is a position of relatively high flux density within the magnetic field of the secondary magnet. When the amount of fluid held by the secondary magnet forms a sufficiently large miniscus, additional fluid captured by the magnet flows to a second region of relatively high flux density in the field of the secondary magnet and is drawn into the voice coil gap.

Abstract: An inclinometer device containing a magnet surrounded at each pole by a thin, discrete band of ferrofluid; these bands are retained against the magnet by its own magnetic field, and suffice to suspend the magnet within a nonmagnetic housing that may be open or closed to the atmosphere. In a first embodiment, a Hall element senses the axial position of the magnet, and a pair of inductor coils, positioned on opposite sides of the neutral point and configured to generate opposing magnetic fields, counteract the magnet's movement and restore it to the neutral position upon application of an appropriate electric current. The magnitude and direction of this restorative current indicate the extent and orientation of the tilt. In a second embodiment, the axial position of the magnet is sensed by a pair of split capacitors disposed on the housing and spaced apart from one another.