CAMBRIDGE, Mass., March 6 -- A researcher at MIT is exploring potential ferrofluid applications in the fields of microelectromechanical and nanoelectromechanical systems (MEMS and NEMS), in particular magnetic-field-driven microfluidic devices.
Ferrofluids are mixtures of carrier liquid (such as water or oil) containing magnetic particles only 10 nanometers, or billionths of a meter, in diameter.
Ferrofluids have been used commercially since the 1960s in applications such as exclusion seals to keep contaminants out of disk drives. They are also used to enhance heat transfer in high-quality audio speakers to allow higher power without overheating.
Markus Zahn, an MIT professor of electrical engineering and computer science who heads the Laboratory for Electromagnetic and Electronic Systems, said "Most conventional MEMS are based on electric fields, but magnetic forces have the advantages that they’re generally larger than electric forces, and there is no electrical breakdown mechanism to cause failure due to spark discharges."
Cory Lorenz, a senior in the same department collaborated on a project with Zahn last summer to explore the effects of time-varying magnetic fields on ferrofluids, which Lorenz videotaped. Lorenz applied the magnetic fields to ferrofluids in a Hele-Shaw cell, where flows are constrained to two dimensions in a small gap between two parallel glass disks. In the first experiment shown on his video, Lorenz applied a 100 Gauss DC vertical magnetic field to a Hele-Shaw cell containing a drop of ferrofluid. This caused the drop to form a spike pattern. He then added a 20 Gauss, 25 Hertz magnetic field that rotates clockwise in the horizontal plane. The result: the ferrofluid slowly changes to a spiral pattern.
By running a typical experiment in reverse order, Lorenz unexpectedly coaxed a ferrofluid to "undergo something analogous to a phase change," Zahn said, resulting in an unexpected pattern.
They noticed that a drop of ferrofluid forms spikes and ultimately forms a spiral when a vertical magnetic field is applied, followed by a rotating field. The changes resulted in designs resembling Native American art, like the one above.
"It was the first time this had ever been observed," said Zahn.
The video was one of five winning entries at last November’s annual meeting of the American Physical Society’s Division of Fluid Dynamics 20th Annual Gallery of Fluid Motion. It will be featured in the September 2003 issue of Physics of Fluids.
For more information, visit: www.mit.edu
The video and a short description are viewable at mit42v.mit.edu/lees/full/faculty/zahn/zahn00.html (requires Windows Media Player).