Dust and mirrors bring smart world closer

Every cranny of the environment could be filled with intelligence if experiments at the University of California at Berkeley fulfil their potential. Researchers working in a wide range of disciplines have created a series of tiny modules, complete with sensors and communications, with the aim of demonstrating 'smart dust' -- self-sustaining network nodes measuring millimetres or less per side.

The new technologies will find uses in environmental monitoring, health, security, distributed processing and tracking -- and doubtless create some uses of their own, including spotting when food is no longer fresh or has been in dangerous conditions. The team also predicts some more unusual devices, such as putting one mote under each fingernail and reporting back on movements -- making invisible keyboards, gesture control and 3D input devices.

Smart dust also has unique problems, many connected with power. While pure radio-frequency ID (RFID) tags just have to send back a unique identifier when interrogated and can use the energy in the interrogating signal, smart dust needs to power sensors, computation, storage and communication. Each of these tasks needs custom designs aimed at reducing power consumption to the bare minimum necessary. Batteries must be very tiny indeed, and while they can be recharged by solar cells or dynamos working from vibrations the power budget can easily be down to nanowatts.

Communications is especially tricky. Radio systems are flexible and reliable, but take relatively high power: most of the signal from any transmission is wasted in space. One of the key innovations the Berkeley scientists are testing is optical links by lasers and mirrors: a mote is illuminated from afar by a laser, and signals back by moving a mirror fabricated as part of a micro electrical mechanical system (MEMS) -- the new nanotechnology of building moving systems on chips.

By building reflectors into a corner-cube retroreflector (CCR) -- three mirrored surfaces at 90 degrees to each other, with the property of sending light back in the direction it came from -- the dust can signal at a great distance with practically no power, of the order of 10,000 times less than by radio. The same laser beam can also carry programs and data into the mote, providing two-way communications. In tests, the researchers have signalled more than 21 kilometres using a standard hand-held laser pointer and electronic sensors: the team says that in principle, it may even be possible to signal to satellites in 300km orbits.

Ultra low power sensing systems are also being developed. Analogue to digital converters -- essential for temperature, pressure, sound and light measurements -- are typically quite power hungry, but a new design works at under 2 microwatts and should be able of nearly halving that. It can also just sample to the level of accuracy required, avoiding the need to do a full 8-bit sample when only a couple of bits of data are required. The team says that with a battery just a cubic millimetre big, the circuit could take ten samples a second for a hundred years. Along similar lines, the team is developing custom processors that have instruction sets designed to encode sensor readings with maximum power efficiency, and to handle communications protocols similarly optimised.

Many prototypes have been demonstrated, most called 'macro-motes' and built out of bigger, commercially available components to prove various concepts. These have included measuring temperature, humidity, barometric pressure, light intensity, tilt and vibration, and magnetic fields all in a cubic inch package, including two-way radio, the microprocessor controller, and the battery. One such prototype was used with the laser pointer signalling system to relay weather information across San Francisco Bay.

The team has acknowledged that smart computers the size of grains of sand monitoring everything around them and sending out signals create some privacy and secrecy issues, but dismiss these as less important than the benefits. Although they've yet to show a fully working mote using the full range of technologies working together, progress is rapid and working examples are expected in a year or so.

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