WANT to build a car the size of a grain of sugar? Or an aircraft no bigger than a mosquito? It is even harder than it sounds 鈥� and not just because assembling small devices is fiddly.
Things are different on the mesoscopic scale. You will find this world as you shrink beyond the millimetre range into the micro and nano worlds, but before you reach the unearthly quantum realm of atoms and electrons.
Here the forces between atoms and molecules are much more significant than they are on our scale. Air, for example, behaves more like vegetable soup than a conventional gas, which means flying is somewhat like wading through treacle.
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Another difference is momentum. On a human scale you can rely on momentum to keep you moving once you have got going. But mesoscopic objects are so small that their momentum is insignificant compared to friction. Stop pushing and they grind to a halt as if they have hit a brick wall.
Then there are the forces we usually ignore in our world. Humans don鈥檛 need to worry about the sparks from static electricity, for example. But on the mesoscopic scale, these sparks are lethal 鈥� get caught by one and it could vaporise you out of existence. The same electrostatic forces that stick a party balloon to the ceiling can root a mesoscopic wheel to the spot. Unwanted charges play havoc with mesoscopic machines.
Why worry? Because a new generation of microelectromechanical (MEM) machines that operate on this scale are beginning to enter our everyday lives. Engineers need to understand the mesoscopic world to make them work reliably.
A few of these devices are already making an impact. The accelerometers that trigger car air bags in a crash are MEM devices operating in the mesoscopic world. So are the chips in digital light projectors. These consist of an array of millions of tiny mirrors that move back and forth to steer beams of light onto a screen.
More machines are on the way. For example, a kind of mesoscopic xylophone that vibrates when struck with radio waves is set to revolutionise the wireless world. These xylophones could replace conventional receivers in cellphones because they can be carved directly into the silicon that makes up the rest of a phone鈥檚 circuitry. This makes them far smaller and cheaper than the receivers in today鈥檚 phones, which are built into separate chips.
This is just the beginning. Mesoscopic aircraft could one day watch over us while submarines on this scale explore our bodies from the inside and carry out repairs. Welcome to the mesoscopic world.
