By Duncan Graham-Rowe, New Scientist . 08.26.99
Cleanliness freaks have a new rationale for their pathological hatred
of dust -- it could soon be spying on them.
Packed full of sensors, lasers and communications transceivers, particles
of "smart dust" are being designed to communicate with one another.
They could be used for a range of applications from weather monitoring
to spying.
The tiny "motes" are being developed at the University of California,
Berkeley, as part of a programme to produce the smallest possible
devices that have a viable way of communicating with each other.
Each mote is made up of a number of microelectromechanical systems,
or MEMS, wired up to form a very simple computer. At present each
mote is 5 millimetres long, but Kris Pister, one of the developers,
says that in future they could be small enough to remain suspended
in air, buoyed by the currents, sensing and communicating for hours.
The latest version not only has a thick-film battery powering it but
also a solar cell to recharge it. "This remarkable package has the
ability to sense and communicate, and is self-powered," says Randy
Katz, a communications engineer on the project. He presented the latest
work at last week's Mobicom99 mobile computing meeting in Seattle.
MEMS are made using the same photolithographic techniques as integrated
circuits, so once perfected they should be easy to mass-produce. Patterns
are etched out of a silicon wafer to create structures such as optical
mirrors or tiny engines.
Each mote in a smart-dust system will need to survive on extremely
low power, while being able to communicate kilobits of data per second.
To this end, says Katz, the team has designed motes that shut down
parts of themselves when they are not being used.
The latest challenge has been to devise a system that enables the
motes to communicate. Katz and his colleagues decided to use optical
transceivers because of their low energy demand compared with radio
communications. According to Pister they have already shown that they
can monitor the dust 21 kilometres across San Francisco Bay. "There's
no way you're going to get that kind of range except with optical
devices," he says.
"The base station may actually reside in a hand-held unit, much like
a pair of binoculars," says Katz. This would allow for simultaneous
viewing of the scene from afar while superimposing any measured data
on the image. He adds that this approach could be especially useful
for hazardous applications such as detecting chemical weapons or sending
the dust into space.
The next task is to build distributed intelligence into the dust to
produce "swarm behaviour."