Abstract: The method of assembling a micro-speaker includes disposing a quantity of volatile magnetic fluid into a radial gap of a driver unit, aligning a vibration system having a diaphragm and a voice coil to the driver unit such that the voice coil is accommodated into the radial gap, fixing the vibration system to the driver unit, and removing the volatile component of the volatile magnetic fluid. The micro-speaker includes a driver unit having a housing, a magnet disposed within the housing forming a radial gap between the magnet and the circumferential walls of the housing, and a magnetic plate disposed on the magnet, a vibration system having a diaphragm and a voice coil where the vibration system is fixed to the drive unit and the voice coil protrudes into the radial gap, and a volatile magnetic fluid in the radial gap about the voice coil.

Abstract: A ferrofluid sealing device retaining a ferrofluid between a shaft and a pair of inner and outer pole pieces rotating in opposite directions, in which grooves are formed on a shaft surface that faces the inner diameter surfaces of pole pieces. In the sealing device, one of the pole pieces may be made thicker than the other and further a projection portion can be formed on the shaft surface facing the inner peripheral faces of the pole pieces. The sealing device can prevent, even when the ferrofluid seal is operated at a higher rotation speed, splashing of ferrofluid over the surroundings, thereby avoiding staining the surroundings as well as prolonging its lifetime.

Abstract: The invention relates to a composition and a process for producing a chemically stable magnetic fluid comprising finely divided magnetic particles covered with surfactants. A surface modifier is also employed which is added to cover thoroughly the free oxidizable exterior surface of the outer layer of the particles to assure better chemical stability of the colloid under different environmental conditions.

Abstract: The present invention relates to a ferrofluid composition having improved oxidation resistance, which contains a carrier liquid, magnetic particles in a stable colloidal suspension, and from more than about 10% to about 400% by weight of an antioxidant based on the weight of the magnetic particles.

Abstract: A magnetic fluid sealing device for preventing magnetic fluid from flowing out or spattering under the influence of rotation of a rotatable shaft, thereby preventing contamination of the surroundings. The device includes a pole piece 1 formed with a step portion 13 whose front end surface 4 is disposed more inwardly than the proximal end surface, and the surface of the step portion 13 opposed to a magnetic body 6 serves as a barrier wall 10. Thereby, magnetic fluid 7 is prevented from flowing out or spattering into the surroundings.

Abstract: A novel magnetic colloid composition containing a polar ester carrier liquid, magnetic particles, and an acid terminated poly (12-hydroxystearic acid) dispersant of the Formula I: ##STR1## where "R" is selected from the group consisting of alkyls, aralkyls, and aryls, substituted or unsubstituted, and "n" is an integer from 0 to 4, or mixtures thereof where "R" and "n" may be the same or different.

Abstract: The invention relates to a composition and a process for producing a chemically stable magnetic fluid comprising finely divided magnetic particles covered with surfactants. A surface modifier is also employed which is added to cover thoroughly the free oxidizable exterior surface of the outer layer of the particles to assure better chemical stability of the colloid under different environmental conditions.

Abstract: The present invention relates to a ferrofluid composition having improved oxidation resistance, which contains a carrier liquid, magnetic particles in a stable colloidal suspension, and from about 5% to about 50% by weight of an antioxidant.