Microscale Pumps, Motors and Turbines Introduce New Era of Miniaturization in Machines
Prof. Reza Ghodssi
|Dr. Reza Ghodssi
The modern-day soldier carries a heavy load. Try to imagine running hard in a desert environment toting some 100 pounds of weapons, body armor, simple medical supplies, food and water, and an array of digital communications and computing devices. Every fatigue-inducing pound matters, including the 20 pounds of lithium ion and other batteries that power those digital devices.
A team of researchers at the A. James Clark School of Engineering, led by Associate Professor Reza Ghodssi and funded by the U.S. Army Research Laboratory and U.S. Army Research Office, has recently succeeded in manufacturing micromachines—tiny pumps, motors, and turbines—that, integrated in a microscale liquid-fuel power generation system, will significantly reduce a soldier’s battery load.
The engineers' advances also hold promise in technologies for health care (micropumps for implantable medical devices) and first responders (bio-chemical sensors).
Using well-known manufacturing techniques similar to those used in the semiconductor industry to make computer chips, the Clark School researchers have successfully miniaturized ball bearing support mechanisms with microballs as wide as a few human hairs and nearly invisible to the naked eye. Using these components, they have built tiny silicon pumps, motors, and turbines demonstrating rotational speeds of up to 87,000 rpm, comparable to the speed of large-scale machinery.
The Clark School team has added ball bearings to the micro-scale world, which gives the designers of micro-electro-mechanical systems (MEMS) devices a very exciting and significantly different bearing option. These bearings should enable the development of MEMS devices that would not be practical with other types of bearings.
In Dr. Ghodssi’s lab, microball bearings have been implemented in electrically-actuated rotary platforms for controlled angular positioning as well as high-speed turbomachinery for microscale fuel pumps. The successful development of these devices will lead directly to the realization of small-scale power generators and high-performance directional sensors systems.
For troops on the battlefield, small-scale combustion generators using such micromachines, and combined with batteries in hybrid technologies, will significantly reduce the soldier’s load.
Micromachine systems also will help power land or air-based "micro vehicles" (also under development at the Clark School in partnership with government agencies) that will venture into risk-filled environments ahead of soldiers or first responders and send back information. Microgenerators fabricated completely in silicon and supported on microball bearings could power the vehicles’ electrical systems without weighing them down.
To create their machines, Ghodssi and his team first had to conquer the science of microscale "tribology" or the friction, wear, and lubrication of tiny rolling components. They then applied this knowledge in building different types of micromachines using conventional manufacturing processes, and finally in integrating these devices into tiny systems that can reliably accomplish a task such as power generation over a reasonable period of time, and not simply burn up.
Rather than focus on an arbitrary performance specification for micromachines, Ghodssi's team focused on feasibility—building pumps and motors that are fast enough to do the jobs required, reliable enough to last, and easy enough to manufacture in the real world. As in the miniaturization of electronics, the researchers expect to achieve successive generations of higher and higher efficiency and refinement in micromachine systems, and to see the creation not only of new defense, medical, and computer products, but of entirely new technologies no one has yet imagined.
Ghodssi was recently featured in a cover story in Mechanical Engineering magazine. The piece focuses on Ghodssi's research on microscale ball bearings for use in micromachines and MEMS devices. Ghodssi explains that ball bearings are crucial in the design of MEMS devices in order to minimize friction and to increase the reliability of the devices.
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