The science of shrinkage: mini guitars and clocks

If angels danced on a pin head, they might strum molecule-size guitars produced by Cornell scientist Paul McEuen and his colleagues. The instrument, a carbon tube just 1.5 micrometers long, vibrates like a guitar string when its ends are clamped down.

Describing their work today in Nature, they don't claim to make music. They do claim to show the potential that tiny carbon tubes have to be part of a so-called nanoelectromechanical system. "Nano" means super small, as in millionths of a meter or less. "Nanoelectromechanical" means the electrical and mechanical parts of macro-world machines mimicked by nano-size gizmos.

Dr. McEuen's carbon nanotubes mimic oscillators in electronic equipment. Chemists are experimenting with structures in which single molecules mimic devices that spin. For example, researchers in Germany have synthesized a molecule that is shaped like - and runs like - a gyroscope rotor. It's a work in progress, yet a report in the American Chemical Society weekly Chemical & Engineering News calls it a step closer to replicating a real toy gyroscope.

Then there's the incredible shrinking atomic clock. A team led by John Kitching at the National Institute of Standards and Technology lab in Boulder, Colo., has shrunk the heart of this highly accurate clock system into a package the size of a rice grain. That's not strictly "nano." But the size reduction is dramatic enough to be part of the micromachine story. So too is the power reduction. A miniature atomic clock based on this device needs only the power of an AA battery. The actual clocks that maintain the world-time standard are power-hungry giants that run up to 2 meters tall.

Atomic clocks work by regulating the time-keeping mechanism, which may be an oscillating crystal, so that it keeps pace with a stable frequency. It's a little like a metronome giving musicians a standard by which to maintain a steady beat. The natural vibrations of cesium atoms provide a steady 9.2 billion beats a second. This is the mechanism Dr. Kitching's team has shrunk. They still would have to add a time-keeping crystal and control electronics to make a clock. Even then, the package would easily fit on a microchip.

This is also a work in progress - one of several projects to shrink atomic clocks. Nevertheless, researchers want to reduce the size further and cut power consumption.

It's hard to foresee just how nano "guitar strings" or gyroscopes will be employed. Yet it seems likely that new machines using microscopic parts are in our future.

The advances will challenge electrical and mechanical engineers used to working within their own well-defined fields.

Engineering professors Steven Girshick at the University of Minnesota in Minneapolis and Arun Majumdar at the University of California in Berkeley put it this way in the journal Nanotechnology: What's involved "is the amalgamation of knowledge from chemistry, physics, biology, materials science, and various engineering fields."

They add that this calls for a reformation to broaden and deepen the education of engineers whose schooling is often more suited to Sputnik-era technology than to the emerging nanotechnical world.

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