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Asmart fluid is afluid whose properties (e.g.viscosity) can be changed by applying anelectric field or amagnetic field.[1][2][3]
The most developed smart fluids today are fluids whose viscosity increases when a magnetic field is applied. Small magnetic dipoles are suspended in a non-magnetic fluid, and the applied magnetic field causes these small magnets to line up and form strings that increase the viscosity. Thesemagnetorheological or MR fluids have been used in thesuspension of the 2002 model of the Cadillac Seville STS automobile and more recently, in the suspension of the second-generation Audi TT. Depending on road conditions, the fluid'sdamping viscosity can be adjusted. This is more expensive than traditional systems, but it provides better (faster) control. Similar systems are being explored to reducevibration inwashing machines,air conditioning compressors, rockets and satellites, and one has even been installed in Japan'sNational Museum of Emerging Science and Innovation inTokyo as anearthquakeshock absorber.
Somehaptic devices whose resistance to touch can be controlled are also based on these MR fluids.
Another major type of smart fluid areelectrorheological or ER fluids, whose resistance to flow can be quickly and dramatically altered by an applied electric field (note, theyield stress point is altered rather than theviscosity). Besides fast actingclutches,brakes,shock absorbers andhydraulic valves, other, more esoteric, applications such as bulletproof vests have been proposed for these fluids.
Other smart fluids change theirsurface tension in the presence of an electric field. This has been used to produce very small controllablelenses: a drop of this fluid, captured in a small cylinder and surrounded by oil, serves as a lens whose shape can be changed by applying an electric field.
The properties of smart fluids have been known for around sixty years, but were subject to only sporadic investigations up until the 1990s, when they were suddenly the subject of renewed interest, notably culminating with the use of an MR fluid on the suspension of the 2002 model of theCadillac Seville STS automobile and more recently, on the suspension of the second-generationAudi TT. Other applications include brakes and seismic dampers, which are used in buildings in seismically-active zones to damp the oscillations occurring in an earthquake. Since then it appears that interest has waned a little, possibly due to the existence of various limitations of smart fluids which have yet to be overcome.[citation needed]
