Smart fluid
Encyclopedia
A smart fluid is a fluid
whose properties (for example the viscosity
) can be changed by applying an electric field
or a magnetic field
.
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
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
in washing machine
s, air conditioning compressors
, rockets and satellites, and one has even been installed in Japan's National Museum of Emerging Science and Innovation in Tokyo
as an earthquake
shock absorber
.
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 point is altered rather than the viscosity
). Besides fast acting clutch
es, brakes, shock absorbers and hydraulic valves
, other, more esoteric, applications such as bulletproof vests have been proposed for these fluids.
Other smart fluids change their surface tension
in the presence of an electric field. This has been used to produce very small controllable lenses
: 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.
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.
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
whose properties (for example the viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
) can be changed by applying an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
or a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
.
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
Magnetorheological fluid
A magnetorheological fluid is a type of smart fluid in a carrier fluid, usually a type of oil. When subjected to a magnetic field, the fluid greatly increases its apparent viscosity, to the point of becoming a viscoelastic solid. Importantly, the yield stress of the fluid when in its active state...
or MR fluids are being used in the suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
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
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
in washing machine
Washing machine
A washing machine is a machine designed to wash laundry, such as clothing, towels and sheets...
s, air conditioning compressors
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
, rockets and satellites, and one has even been installed in Japan's National Museum of Emerging Science and Innovation in Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
as an earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
shock absorber
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
.
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
Electrorheological fluid
Electrorheological fluids are suspensions of extremely fine non-conducting particles in an electrically insulating fluid. The apparent viscosity of these fluids changes reversibly by an order of up to 100,000 in response to an electric field...
or ER fluids, whose resistance to flow can be quickly and dramatically altered by an applied electric field (note, the yield stress point is altered rather than the viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
). Besides fast acting clutch
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...
es, brakes, shock absorbers and hydraulic valves
Hydraulic manifold
A hydraulic manifold is a component that regulates fluid flow between pumps and actuators and other components in a hydraulic system. It is like a switchboard in an electrical circuit because it lets the operator control how much fluid flows between which components of a hydraulic machinery...
, other, more esoteric, applications such as bulletproof vests have been proposed for these fluids.
Other smart fluids change their surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
in the presence of an electric field. This has been used to produce very small controllable lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
: 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 SevilleCadillac Seville
The Cadillac Seville is a luxury-type car that was manufactured by the Cadillac division of American automaker General Motors from 1975 to 2004, as a smaller-sized top-of-the-line Cadillac...
STS automobile and more recently, on the suspension of the second-generation Audi TT
Audi TT
The Audi TT is a two-door sports car manufactured by the German automaker and Volkswagen Group subsidiary Audi since 1998.The Audi TT has been produced in two generations. Both generations have been available in two car body styles; as a 2+2 Coupé, or two-seater Roadster...
. 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.
See also
- Continuum mechanicsContinuum mechanicsContinuum mechanics is a branch of mechanics that deals with the analysis of the kinematics and the mechanical behavior of materials modelled as a continuous mass rather than as discrete particles...
- Electrorheological fluidElectrorheological fluidElectrorheological fluids are suspensions of extremely fine non-conducting particles in an electrically insulating fluid. The apparent viscosity of these fluids changes reversibly by an order of up to 100,000 in response to an electric field...
- FerrofluidFerrofluidA ferrofluid is a liquid which becomes strongly magnetized in the presence of a magnetic field.Ferrofluids are colloidal liquids made of nanoscale ferromagnetic, or ferrimagnetic, particles suspended in a carrier fluid . Each tiny particle is thoroughly coated with a surfactant to inhibit clumping...
- Fluid mechanicsFluid mechanicsFluid mechanics is the study of fluids and the forces on them. Fluid mechanics can be divided into fluid statics, the study of fluids at rest; fluid kinematics, the study of fluids in motion; and fluid dynamics, the study of the effect of forces on fluid motion...
- Magnetorheological fluidMagnetorheological fluidA magnetorheological fluid is a type of smart fluid in a carrier fluid, usually a type of oil. When subjected to a magnetic field, the fluid greatly increases its apparent viscosity, to the point of becoming a viscoelastic solid. Importantly, the yield stress of the fluid when in its active state...
- RheologyRheologyRheology is the study of the flow of matter, primarily in the liquid state, but also as 'soft solids' or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force....
- Smart glass
- Smart metal