US Patent 7419616 - Fluidic switch using interlocking magnetic particles

http://www.freepatentsonline.com/7419616.html

Magnetorheological fluids have the property of variable viscosity dependent on magnetic fields which is useful for flow control switches. This patent from GM teaches controlling the aspect ratios of the particles forming these fluids to maintain a high and stable on/off ratio for the flow. Claims 1 and 15 read:

1. A magnetorheological fluid composition comprising: a carrier fluid; and a plurality of low aspect ratio magnetizable particles with interlocking structures.

15. A magnetorheological fluid composition comprising: a carrier fluid; and a plurality of high aspect ratio magnetizable particles comprising interlocking structures.