John Austin, science educator at Discovery Place in Charlotte, N.C., uses magnetorheological (MR) fluid to help introduce basic engineering concepts to fourth-graders in the museum’s Technology for Young Engineers program.
“I tie it into my classes on bridge building,” he said. “Kids are always asking, ‘Why do I need to take all this math? Why do I need all this science?’” So he starts off by showing them a film of the Tacoma Narrows Bridge that in 1940 fell to pieces because of wind vibration. “‘Here’s an example of people who didn’t quite understand the mathematics of bridge building,’ I tell them. I challenge the students.”
The kids mold and shape MR fluid using a magnet to vary the solidity of the material, and it never fails to amaze them, Austin said. MR fluid is great for the classroom because it’s easy to use.
Think of the dirtiest motor oil you’ve ever seen and that’s pretty much what MR fluid looks like. It’s a carrier liquid—water, hydrocarbon (mineral) oil or silicone oil—with tiny particles of iron suspended in it. Apply a magnetic field, and the little iron bits line up to form chains and the fluid becomes a semisolid.
Move the magnet away, weakening the field, and the semisolid transforms instantly into a more liquid state. Move the magnet closer and it becomes more solid.
Simple. And you can make it yourself. Crush up some Total breakfast cereal to get at the carbonyl iron that’s good for your body, crumble it into some corn oil and stir. Add strong magnet.
Now what? That’s basically the question scientists have been asking since inventor Jacob Rabinow received the first patent for MR fluid in the 1940s. A laboratory curiosity with little practical use for decades, researchers began to get serious about it in the late 1980s and 1990s, when other technologies began to converge that made practical use of MR fluid a real possibility.
Microprocessors and sensor technology created control that didn’t exist before. Battery technology, fueled by the advance of the burgeoning cell phone industry, provided power in small packages never before possible. Manufacturing processes reached a level of sophistication necessary to produce flawless, micron-size spheres of carbonyl iron required for the subtle control and durability MR fluid required to be practical.
Still, new technologies aside, moving this new material from lab to commercialization faced huge hurdles.
And because the material was new, engineers didn’t quite know how to incorporate it into designs that would force them to scrap conventional thinking. So, Lord Corp. engineers invented their own MR devices—controllable dampers and rotary brakes, control algorithms and power supplies—to demonstrate how the material functioned and how it would look in a real application.
As a result, the past few years have seen MR fluids and devices incorporated into automotive shock absorbers, driver seat suspensions for truck and heavy equipment operators and in industrial vehicle steering systems. They’re in buildings and bridges to dissipate energy from earthquakes and wind as well as in factory machines to control motion. MR fluid devices have been used to develop a controllable artificial knee for amputees, to control vibration in spinning washing machines and to manage satellite equipment in space orbit.
Engineers and scientists continue to explore new applications as well, in fields as diverse as automotive crash protection systems, offshore oil-drilling platform stabilizers and virtual reality simulators for surgeons.
