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What is Magnetorheological Fluid?

Michael Anissimov
Updated Jan 27, 2024
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A magnetorheological fluid is a fascinating smart fluid with the ability to switch back and forth from a liquid to a near-solid under the influence of a magnetic field. It is usually used for applications in braking. The term "magnetorheological fluid" comes from a combination of magneto, meaning magnetic, and rheo, the prefix for the study of deformation of matter under applied stress. Magnetorheological fluids are not currently in wide use but are considered a futuristic type of material.

The method of operation of a magnetorheological fluid is simple. A magnetorheological fluid is made up of micrometer-sized ferroparticles, particles like iron that respond to a magnetic field, suspended in an oil-based medium. When outside the influence of a magnetic field, the particles float freely, causing the material to behave like any colloidal mixture, such as milk. When a magnetic field is turned on, however, the ferroparticles align in vertical chains along the field's flux lines, restricting the fluid flow and increasing the viscosity up to around that of a weak plastic.

Because the strength of the magnetorheological fluid comes from aligned ferroparticles that only make up a minority of the overall mixture, there are definite limits to how strong it can be, but the significant difference between the "off" and "on" modes makes it appealing for use in a variety of applications where conventional brakes are ineffective. Typically, the magnetorheological fluid is kept between two small plates, only a few millimeters apart, which maximizes the mixture's braking properties. The system must be arranged such that the magnetic flux lines are perpendicular to the direction of motion to be stopped.

For circular motion, one of the best target applications, imagine a rotor with spokes spinning freely in a magnetorheological fluid. When the rotor must be stopped, a series of small magnets produces magnetic flux lines that radiate away from the center rotor, creating ferroparticle chains in the medium like rays pointing away from the sun. These rays catch on the spokes, radically slowing them. Even if the spokes break through the aligned particles, the persistent magnetic field causes them to quickly realign, ready to catch the next incoming spoke. This arrangement provides a powerful rotary brake.

Research groups are investigating other possible applications for magnetorheological fluid, such as body armors which are flexible but quickly become rigid upon contact with an incoming bullet.

AllTheScience is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Anissimov
By Michael Anissimov

Michael is a longtime AllTheScience contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

Discussion Comments

By anon275139 — On Jun 16, 2012

Where can I buy permanent magntorhological fluid?

Give some hints.

By anon114462 — On Sep 28, 2010

I am working on a final year project that involves the use of the magnetorheological fluid in a vibration absorber. Any tips for me, it will be greatly appreciated. Thanks in advance!

By anon64863 — On Feb 09, 2010

i'm interested in creating a Mr damper for controlling tool vibration. how to determine the size of iron particles and the fluid? What will happen if them viscosity of the oil is increased?

By anon28905 — On Mar 24, 2009

I want to know how to get the ingredients & how to combine them correctly?

By anon24449 — On Jan 12, 2009

Hello. My sixth grade son has a science fair coming up. His teacher mentioned magnetorheological fluid which got him all excited. Any ideas about a SIMPLE experiment he can do with this would be greatly appreciated. Thank you!

Michael Anissimov

Michael Anissimov

Michael is a longtime AllTheScience contributor who specializes in topics relating to paleontology, physics, biology...

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