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: A long-life, stacked pole-piece magnetic fluid seal for sealing between a housing and magnetically permeable shaft, in one embodiment is comprised of an annular magnet, having poles of opposite polarity on first and second end surfaces thereof, an annular, magnetically permeable primary pole-piece axially abutting the first end surface of the magnet, and one or more annular, magnetically permeable secondary pole-pieces stacked axially adjacent the primary pole-piece and separated therefrom and from each other by one or more annular spacers which define intermediate spaces between the pole-pieces. The pole-pieces are in a closely-spaced, non-contacting relationship with the shaft to define one or more radial gaps which, in conjunction with the intermediate spaces collectively form an annular ring in which a magnetic fluid is disposed and retained. In a second embodiment, the annular magnet is separated from the primary pole piece by a spacer which defines an intermediate space therebetween.

Abstract: A multi-stage ferrofluid seal incorporates a ferrofluid reservoir for extending seal life. The reservoir is located between seal stages and contains a quantity of ferrofluid sufficient to replace ferrofluid in the seal stages which is lost due to evaporation or contamination. The seal is designed to withstand a pressure drop between a high pressure area and a low pressure area and the location of the reservoir is selected so that the pressure capacity of the seal stages between the low pressure area and the reservoir is sufficient to withstand the entire pressure drop. The pressure capacity of the seal stages between the high pressure area and the reservoir is less than the entire pressure drop. Failure of the seal stages between the reservoir and low pressure area causes failure of the seal stages between the reservoir and the high pressure area.