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Ferrofluid Reservoir Storage in a Ferrofluid Display

IP.com Disclosure Number: IPCOM000083298D
Original Publication Date: 1975-Apr-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Romankiw, LT: AUTHOR [+3]

Abstract

In general, a system or a display employing ferrofluid droplets requires the confining of excess fluid to a restricted area, from which the fluid is removed as required to form new droplets. Since the ferrofluid droplets, unlike magnetic bubble domains, are magnetic fluid droplets in a nonmagnetic host having volume and mass, they cannot collapse (be annihilated) or be generated (created) but must, by manipulating the magnetic field, be formed by drawing from a reservoir (a body of magnetic fluid) and be returned to the reservoir when its immediate usefulness has expired. Design of a ferrofluid reservoir used in construction of a display must take into account (a) gravity force, (b) surface tension and capillary forces and, (c) magnetic (attraction) forces.

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Ferrofluid Reservoir Storage in a Ferrofluid Display

In general, a system or a display employing ferrofluid droplets requires the confining of excess fluid to a restricted area, from which the fluid is removed as required to form new droplets. Since the ferrofluid droplets, unlike magnetic bubble domains, are magnetic fluid droplets in a nonmagnetic host having volume and mass, they cannot collapse (be annihilated) or be generated (created) but must, by manipulating the magnetic field, be formed by drawing from a reservoir (a body of magnetic fluid) and be returned to the reservoir when its immediate usefulness has expired. Design of a ferrofluid reservoir used in construction of a display must take into account (a) gravity force, (b) surface tension and capillary forces and, (c) magnetic (attraction) forces.

Gravity of the host solution can be matched to that of the ferrofluid (which is a desirable case, because the display can thin operate in either a vertical or horizontal position) so the forces involved are primarily (b) and (c). Thus, the reservoir is a ferrofluid droplet "concentrator", in which the concentration is accomplished using magnetic and capillary forces. The magnetic force can be either applied using an electromagnet or using a permanent magnet. Permanent Magnet Case-Magnetic Forces Dominating.

In this case, a permanent magnet is used so the capillary forces need not be dominating (very large). The concentration of droplets and holding of the body of the fluid results from the magnetic field gradient near the permanent magnet. Electromagnet Case 1 Capillary Forces Dominating.

In this case, an electromagnet is used to concentrate the droplets. There are large capillary forces for the reservoir to remain in place when the display is moved or shaken, while the electrical current to the electromagnet is shut off. Since, from the point of view of ease of formation of droplets, it is desired not to have excessively large capillary forces acting on the ferrofluid, the permanent magnet case and m...