A smart fluid is a

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

whose properties (e.g.

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

) can be changed by applying an

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

or a

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

. 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. These magnetorheological or MR fluids are being used in the

suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspend ...

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 damping fluid's viscosity is adjusted. This is more expensive than traditional systems, but it provides better (faster) control. Similar systems are being explored to reduce

vibration Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic function, periodic, such as the motion of a pendulum ...

washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...

s, air conditioning compressors, rockets and satellites, and one has even been installed in Japan's

National Museum of Emerging Science and Innovation The , simply known as the , is a museum created by Japan's Science and Technology Agency. It was opened in 2001. It is situated in a purpose-built building in the Odaiba District of Tokyo. It can be reached by the Yurikamome driverless fully au ...

Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, with an estimated 37.468 ...

as an

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

shock absorber A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Most sh ...

. Some haptic devices whose resistance to touch can be controlled are also based on these MR fluids. Another major type of smart fluid are electrorheological or ER fluids, whose resistance to flow can be quickly and dramatically altered by an applied electric field (note, the

yield stress In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and wi ...

point is altered rather than the

). Besides fast acting

clutch A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...

es,

brakes A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...

shock absorbers A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Most sh ...

and hydraulic valves, other, more esoteric, applications such as bulletproof vests have been proposed for these fluids. Other smart fluids change their

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f ...

in the presence of an electric field. This has been used to produce very small controllable

lenses A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

: 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.

Background

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 the

Cadillac Seville The Seville was manufactured by Cadillac from 1975 to 2004 as a smaller-sized, premium model. It was replaced by the STS in 2004. Origin of the name The name of "Cadillac's first small car" was selected over a revival of LaSalle or the GM des ...

STS automobile and more recently, on the suspension of the second-generation Audi 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.{{Fact, date=February 2007

References

*https://web.archive.org/web/20070113154425/http://www.aip.org/tip/INPHFA/vol-9/iss-6/p14.html Smart materials Fluid dynamics

Background

See also

References