View source for Smart fluid

{{Short description|Fluid whose properties can be changed by applying an electric or magnetic field}}
{{Lead too short|date=June 2025}}
{{Electromagnetism}}
{{Distinguish|SmartWater}}
{{Continuum mechanics|cTopic=rheology}}

A '''smart fluid''' is a [[fluid]] whose properties (e.g. [[viscosity]]) can be changed by applying an [[electric field]] or a [[magnetic field]].<ref>{{Cite web |title=Smart Fluid Properties and Applications |url=https://www.ijies.net/finial-docs/copyrightform/19513825102018pdf...pdf}}</ref><ref>{{Cite web |title=Smart fluids - Knowledge and References |url=https://taylorandfrancis.com/knowledge/Engineering_and_technology/Materials_science/Smart_fluids/ |access-date=2024-11-25 |website=Taylor & Francis |language=en-US}}</ref><ref>{{Cite journal |last1=Yin |first1=Jianbo |last2=Zhao |first2=Xiaopeng |date=2011-03-25 |title=Electrorheology of nanofiber suspensions |journal=Nanoscale Research Letters |language=en |volume=6 |issue=1 |pages=256 |doi=10.1186/1556-276X-6-256 |issn=1556-276X |pmc=3211318 |pmid=21711790 |doi-access=free|bibcode=2011NRL.....6..256Y }}</ref>

== History ==

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]] 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}}

== Examples ==

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 fluid|magnetorheological]] or MR fluids have been used in the [[suspension (vehicle)|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 fluid's [[Viscous damping|damping viscosity]] can be adjusted. This is more expensive than traditional systems, but it provides better (faster) control. Similar systems are being explored to reduce [[oscillation|vibration]] in [[washing machine]]s, [[air conditioning|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 technology|haptic]] devices whose resistance to touch can be controlled are also based on these MR fluids.

Another major type of smart fluid are [[Electrorheological fluid|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 manifold|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 [[Lens (optics)|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.

== See also ==

* {{anl|Continuum mechanics}}
* {{anl|Electrorheological fluid}}
* {{anl|Ferrofluid}}
* {{anl|Fluid mechanics}}
* {{anl|Magnetorheological fluid}}
* {{anl|Rheology}}
* {{anl|Smart glass}}
* {{anl|Smart metal}}

== References ==

{{refs}}

[[Category:Smart materials]]
[[Category:Fluid dynamics]]