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Micromachines
| Article
# : |
19124 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
1 / 1991 |
2,914 Words |
| Author
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Stephen D. Senturia
Stephen D. Senturia is the Barton L. Weller Professor of
Electrical Engineering at the Massachusetts Institute of
Technology. |
What is a micromachine? We are all familiar with "macromachines" like cars and elevators. A micromachine is simply a very small machine. A useful dimensional boundary between the macro and the micro worlds is about 1 millimeter, which equals 1,000 micrometers (or microns, abbreviated um).
In 1959, the eminent physicist Richard Feynman, fascinated with what might be possible in this micro domain, offered a prize for the engineer who could make the world's smallest electric motor. This prize was awarded in 1960 to William McLellan for a motor about 1 millimeter on a side. The machines we shall discuss here have moving parts as small as 10 to 100 um across, too small to see clearly without a microscope.
As commonly used, the term machine is loosely applied to both very complex and very simple devices. Micromachines, at this stage of development, are necessarily simple. For purposes of this article, a "machine" consists of a moving mechanism driven by a source of mechanical energy (called an actuator) which must in turn be supplied by a primary energy source. In practice there is often a complex drivetrain connecting the actuator and the mechanism.
Even a relatively simple machine, such as a bicycle, is complex in comparison with the present generation of micromachines. In a bicycle, the actuator is the human rider. The force is delivered from the actuator to the mechanism, the bicycle, through the drivetrain--pedals, gears, chain, and rear wheel. The bicycle's drivetrain effectively converts reciprocating motion (up and down movement of the feet) to rotary motion through the pedals. The energy source is the food, water, and air consumed by the rider.
The conversion of reciprocating motion to rotary motion is integral to the propulsion of automobiles as well as steam engines--pistons go up and down, wheels go round and round. Reciprocating motion also can be used directly--for example to pump fluids, and thus to operate hydraulic or pneumatic mechanisms. A revolution in fabrication technologies that started in 1985 has enabled us to build microscopic versions of rotory actuators, reciprocating actuators, and mechanisms. Thus is born the field of micromachines.
How Might We Use Them?
The first question people ask about micromachines is what they might be used for. Micromachines have several unique features: They are small; they are fast;
...
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