By Candace Stuart
Small Times Senior Writer
They’re as thin as a strand of hair. The size of a grain of salt. Dwarfed by dust mites.
MEMS have been reduced to a handful of micro-metaphors as disciples try to explain in familiar terms how small the devices really are. But hair
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| The largest gear in this MEMS device is about 100 microns across. Photo courtesy Sandia National Laboratories |
Dust mites — let’s just leave them under the microscope.
For clarity, we at Small Times have decided to offer a guide, if not for the industry, for ourselves. To avoid seeming arbitrary, we consulted with Russ Rowlett, director of the Center for Mathematics and Science Education at the University of North Carolina at Chapel Hill and author of the online Dictionary of Units and Measurements .
By his calculations, the conventional estimate for a width of human hair is 0.1 millimeter, which is 100 microns. In American measurement lingo, that is 0.004 inches.
Manufacturers control the coarseness of the salt they produce, he found, but most grains fit in the 0.3-0.5 millimeter range. That’s 300 to 500 microns, or 0.012 to 0.02 inches. (You begin to see the advantages of the metric system.)
The printed acronym MEMS at 12 point in the font Times New Roman is about 12,500 microns, give or take a hair’s breadth. Many sources use the unit micron, which is one millionth of a meter, although the General Conference on Weights and Measures dropped the term in the 1960s.
Here are some prefixes commonly used in measurements for MEMS and nanotechnologies:
Micro = a millionth or 0.000001
This is the realm where MEMS stand tall. The Amazons of MEMS can reach up to 10 millimeters. A millimeter is a thousandth of a meter, or 1,000 times bigger than a micron. But a typical MEMS device such as a gear is more likely to measure 100 microns or less. Components, on the other hand, can be as tiny as a mere micron.
Some of the best known applications of MEMS have been in airbags and inkjet printers. The airbag includes an accelerometer that measures in microns. It will trigger the deployment of the airbag when it senses either a shift in mass or internal stress from the jolt and crunch of a crash.
Inkjets have a minute MEMS nozzle that emits precise droplets of ink. Depending on the purpose, the droplets can be 10 microns, or even smaller.
Nano = a billionth or 0.000000001
Engineers say MEMS is a process of building down, of taking a machine and making it much smaller. MEMS is based on man’s creations.
Nanotechnology mimics nature, which crafts molecules atom by atom, or tissues cell by cell. Nanotechnology is the process of building up, using the blueprints of matter to design tools so small they can float in the blood stream.
Nanotechnology got a boost in 2000 with the official creation of the National Nanotechnology Initiative. The program, which received a total of $497 million for fiscal 2001, supports research on nature’s fundamental building blocks.
Among those building blocks is the nanotube, elongated molecules that — depending on their chemical composition — may conduct electricity or bear loads. A carbon nanotube wire, for instance, has a diameter of 1.4 nanometers, or a width of 10 atoms, and is conductive.
IBM researchers reported in late April that they used carbon nanotubes to construct transistors that spanned a few molecules. Their goal is to shrink the components in a computer by several hundredths.
Pico = a trillionth or 0.000000000001
Remember those tiny droplets from inkjet printers? The photography and imaging company Eastman Kodak’s research and development branch has found a way to produce ink droplets as refined as 2 to 3 picoliters.
But more often pico is presented in terms of space exploration. The Defense Advanced Research Project Agency has developed a tiny satellite the size of a deck of cards. Picosatellites must weigh less than a kilogram, and one prototype is even lighter: 250 grams. Russia’s Sputnik, by comparison, weighed 84 kilograms.
Femto = a quadrillionth or 0.000000000000001
OK, that’s a lot of lot of zeroes. Femto is more often used as a temporal term than as a spatial one. Physicists and engineers who work on the smallest of scales now need tools that operate at ultrafast speeds.
Some lasers now emit optical pulses in periods as short as 10 femtoseconds. The laser bursts can remove atoms on the surface of the target material with no or little thermal damage to the material. Femtosecond lasers are an emerging technology that could have a critical role in the development of nanoscale machines. By working in femtoseconds, engineers can manipulate material with molecular precision.
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CONTACT THE AUTHOR:
Candace Stuart at [email protected] or call 734-994-1106, ext. 233.
IMAGES:
* Cover: Individual carbon atoms can lock together to form a symmetrical nanotube, as shown in this model. Photo courtesy Richard Smalley/Rice University.
* Gear: The largest gear in this MEMS device is about 100 microns across. The gears are part of a microengine designed by scientists at Sandia National Laboratories. Photo courtesy Sandia.