Editing Magnetorheological fluid (section)

{{Short description|Type of smart fluid in a carrier fluid}}
{{Electromagnetism}}
[[File:MRF-Effekt-static-crop.png|thumb|Schematic of a magnetorheological fluid solidifying and blocking a pipe in response to an external magnetic field. ([http://upload.wikimedia.org/wikipedia/commons/2/2e/MRF-Effekt.gif Animated version available.])]]
{{Continuum mechanics|cTopic=rheology}}

A '''magnetorheological fluid''' ('''MR fluid''', or '''MRF''') 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.<ref>{{Cite journal |last1=Bahl |first1=Shashi |last2=Nagar |first2=Himanshu |last3=Singh |first3=Inderpreet |last4=Sehgal |first4=Shankar |date=2020-01-01 |title=Smart materials types, properties and applications: A review |url=https://www.sciencedirect.com/science/article/pii/S2214785320331278 |journal=Materials Today: Proceedings |series=International Conference on Aspects of Materials Science and Engineering |volume=28 |pages=1302–1306 |doi=10.1016/j.matpr.2020.04.505 |s2cid=219435304 |issn=2214-7853|url-access=subscription }}</ref> Importantly, the yield stress of the fluid when in its active ("on") state can be controlled very accurately by varying the magnetic field intensity. The upshot is that the fluid's ability to transmit force can be controlled with an [[electromagnet]], which gives rise to its many possible control-based applications.

MR fluid is different from a [[ferrofluid]] which has smaller particles. MR fluid particles are primarily on the [[micrometre]]-scale and are too [[density|dense]] for [[Brownian motion]] to keep them suspended (in the lower density carrier fluid). Ferrofluid particles are primarily [[nanoparticles]] that are suspended by Brownian motion and generally will not settle under normal conditions. As a result, these two fluids have very different applications.