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April 2001

News about Science, Technology and Engineering at Iowa State University

Buckybowls by the bucketful
Scientists may be closer to unlocking the mystery of buckyballs, curious hollow spheres formed by 60 atoms of carbon, thanks to research being conducted by Peter Rabideau, dean of Iowa State University's College of Liberal Arts and Sciences and a senior chemist at the Department of Energy's Ames Laboratory.

Since the buckyball's geodesic structure is very stable and hollow, chemists have envisioned a whole new array of applications if they could find a way to put other atoms or compounds inside the buckyball. Unfortunately, the only way to produce C60 is with a process that basically involves arcing carbon rods. The high temperatures make it hard to control, and therefore extremely difficult to try to make buckyballs with something inside them. So the search turned to finding a way to "build" a buckyball from scratch.

Using simple solution chemistry, Rabideau has developed a process to produce gram quantities of corannulene (C20), a curved-surface, aromatic hydrocarbon. Nicknamed buckybowls, the bowl-shaped corannulene molecules represent the "polar cap" of the C60 sphere. By making it possible to produce large quantities of these bowl segments, Rabideau hopes to piece together a complete buckyball. For more information, contact Rabideau, (515) 294-3220, or Kerry Gibson, Ames Lab Public Affairs, (515) 294-1405.

Sensing noise and canceling it
Acoustic noise control research at Iowa State University might help take the ringing out of airplane travel. In a $220,000 project with NASA Langley Research Center, Hampton, Va., Atul Kelkar, an associate professor of mechanical engineering, aims to quench the noise of machinery in an enclosed environment, like that generated in an airplane cabin from the plane's engines and fuselage.

Kelkar's approach uses active feedback control to modify the interior acoustic dynamics of the cabin in such a way that helps suppress the noise. Most current noise control methods use "feed-forward cancellation" techniques, which send out a secondary noise that attempts to cancel the primary one. These methods are effective for control of tonal noise and harmonics. "The ultimate goal is to have robust, broadband noise reduction in the cabin as opposed to only tonal noise and harmonics," Kelkar says.

"Existing methods sense the noise signal upstream and then invert its phase and put it downstream to cancel it," he explains. "But these methods are most effective for only tonal noise at few selected frequencies. Our method provides active control of noise in that it senses the noise and then generates a feedback control signal that extracts the acoustic energy in the closed-loop system and, hence, renders silence. The method works over a wide range of frequencies and provides robust control of noise."

The new method is based on research by Kelkar that has demonstrated energy extraction techniques in closed-loop systems. Part of the new project will be to develop an integrated control design for simultaneous control of the interior acoustic pressure field and structural vibrations to help dissipate the energy in the closed-loop configuration. In other words, Kelkar says, his system will not only use active acoustic feedback, but also will modify the interior's structural response to the noise to help quiet it.

Kelkar says the method, if further refined, could find use beyond airplanes and aerospace structures to machinery in closed rooms, ranging from manufacturing environments to washers, dryers, lawn mowers and vacuum cleaners. For more information, contact Kelkar, (515) 294-0788, or Skip Derra, ISU News Service, (515) 294-4917.

Protective polymer coatings for MEMS
An Iowa State University professor's NSF-funded research on the microstructure of polymers is yielding significant applications in the electronics industry. Vladimir Tsukruk of ISU's materials science and engineering department and a multidisciplinary research team have developed innovative ultra-thin polymer coatings that provide improved protection of micro-electromechanical systems (MEMS) from damage caused by environmental contamination and repeated use.

Tsukruk's method involves using a self-assembly electrostatic process to form specially tailored nano-composite coatings that contain flexible and hard layers. These molecular thin films, which are less than 10 nanometers thick, have extremely low friction, low adhesion and a much longer life span than existing monolayered polymer interfaces. When applied to movable parts in MEMS, which often range in the vicinity of 5 to 20 micrometers (or about the thickness of two strands of hair), the new coating provides 10 times more stability than conventional coatings.

Tsukruk also is investigating hyperbranched and dendrimer polymers, a new class of polymers whose unusual molecular architecture show promise as interface materials, he says. Tsukruk also sees potential of other polymer applications in biomimetics, or biological thermal sensing, with the ultimate goal of designing "soft-matter" thermal sensors that imitate those found in nature, like in reptiles and other animals. For more information, contact Tsukruk, (515) 294-6904, or Sunanda Vittal, Engineering Communications, (515) 294-8787.


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