MR Fluid Magnetorheological Fluid

Above, MR fluid prior to magnetization. Below, the fluid turned into a solid after it was magnetized. Notice the shiny surface of the liquid in
the top photo and the dull surface in the bottom photo.

What is MR Fluid
Looking at it in a beaker, MR fluid doesn't seem like such a revolutionary substance. It's a gray, oily iquid that's about three times denser than water. It's not too exciting at first glance, but MR fluid is actually quite amazing to watch in action.

A simple demonstration by David Carlson, a physicist at the North Carolina lab, shows the liquid's ability to transform to solid in
milliseconds. He pours the liquid into the cup and stirs it around with a pencil to show it's liquid. He then places a magnet to the bottom of the cup, and the liquid instantly turns to a near-solid. To further demonstrate that it's
turned to a solid, he holds the cup upside down, and none of the MR fluid drops out.(

Typical MR fluid consists of these three parts:

  • Carbonyl Iron Particles -- 20 to 40 percent of the fluid is made of these soft iron particles that are just 3 to 5 micrometers in diameter. A package of dry carbonyl iron particles looks like black flour because the particles are so fine.
  • A Carrier Liquid -- The iron particles are suspended in a liquid, usually hydrocarbon oil. Water is often used in demonstrating the fluid.
  • Proprietary Additives -- The third component of MR fluid is a secret, but Lord says these additives are put in to inhibit gravitational settling of the iron particles, promote particle suspension, enhance lubricity, modify viscosity and inhibit wear.


So, what is it that gives MR fluid its unique ability to transform from liquid to solid and from solid to liquid quicker than you can blink an eye? The carbonyl iron particles. When a magnet is applied to the liquid, these tiny particles line up to make the fluid stiffen into a solid. This is caused by the dc magnetic field, making the particles lock into a uniform polarity. How hard the substance becomes depends on the strength of the magnetic field. Take away the magnet, and the particles unlock immediately.(

1_(2).jpgOver fifty years ago both Rabinow and Winslow described basic MR fluid formulations that were every bit as strong as fluids today. A typical MR fluid used by Rabinow consisted of 9 parts by weight of carbonyl iron to one part of silicone oil, petroleum oil or kerosene.1 To this suspension he would optionally add grease or other thixotropic additive to improve settling stability. The strength of Rabinow’s MR fluid can be estimated from the result of a simple demonstration that he performed. Rabinow was able to suspend the weight of a young woman from a simple direct shear MR fluid device. He described the device as having a total shear area of 8 square inches and the weight of the woman as 117 pounds. For this demonstration to be successful it was thus necessary for the MR fluid to have yield strength of at least 100 KPa.

Current industrial applications

Mechanical engineering

Magnetorheological dampers of various applications have been and continue to be developed. These dampers are mainly used in heavy industry with applications such as heavy motor damping, operator seat/cab damping in construction vehicles, and more.
As of 2006, materials scientists and mechanical engineers are collaborating to develop stand-alone seismic dampers which, when positioned anywhere within a building, will operate within the building'sresonance frequency, absorbing detrimental shock waves and oscillations within the structure, giving these dampers the ability to make any building earthquake-proof, or at least earthquake-resistant. (

Military and defense

The U.S. Army Research Office is currently funding research into using MR fluid to enhance body armor. In 2003, researchers stated they were five to ten years away from making the fluid bullet resistant. In addition, Humvees, and various other all-terrain vehicles employ dynamic MR shock absorbers and/or dampers.


Magnetorheological finishing, a magnetorheological fluid-based optical polishing method, has proven to be highly precise. It was used in the construction of the Hubble Space Telescope's corrective lens.

Automotive and aerospace

1_(1).pngIf the shock absorbers of a vehicle's suspension are filled with magnetorheological fluid instead of plain oil, and the whole device surrounded with an electromagnet, the viscosity of the fluid, and hence the amount of damping provided by the shock absorber, can be varied depending on driver preference or the weight being carried by the vehicle - or it may be dynamically varied in order to provide stability control. This is in effect a magnetorheological damper. For example, the MagneRide active suspension system permits the damping factor to be adjusted once every milisecond in response to conditions. General Motors (in a partnership with Delphi Corporation) has developed this technology for automotive applications. It made its debut in both Cadillac (Seville STS build date on or after 1/15/2002 with RPO F55) as "Magneride" (or "MR") and Chevrolet passenger vehicles (All Corvettes made since 2003 with the F55 option code) as part of the driver selectable "Magnetic Selective Ride Control (MSRC)" system) in model year 2003. Other manufacturers have paid for the use of it in their own vehicles. As of 2007, BMW manufactures cars using their own proprietary version of this device, while Audi and Ferrari offer the MagneRide on various models.
General Motors and other automotive companies are seeking to develop a magnetorheological fluid based clutch system for push-button four wheel drive systems. This clutch system would useelectromagnets to solidify the fluid which would lock the driveshaft into the drive train.
Magnetorheological dampers are under development for use in military and commercial helicopter cockpit seats, as safety devices in the event of a crash. They would be used to decrease the shock delivered to a passenger's spinal column, thereby decreasing the rate of permanent injury during a crash. (

Human prosthesis

Magnetorheological dampers are utilized in semi-active human prosthetic legs. Much like those used in military and commercial helicopters, a damper in the prosthetic leg decreases the shock delivered to the patients leg when jumping, for example. This results in an increased mobility and agility for the patient.(

farther info& references
Done by: Peter Ehab