Researchers Create Wireless Sensor Chip the Size of Glitter
The chip will be the brains behind the new generation mote, dubbed "Spec" by its creators. It's a significant milestone in the Smart Dust and TinyOS projects, which are part of UC Berkeley's Center for Information Technology Research in the Interest of Society (CITRIS). The projects seek to create low-powered, low-cost wireless sensor devices, or motes, roughly the size of a grain of sand.
Massive numbers of these millimeter-scaled motes could be used in self-organizing wireless sensor networks for such innovative applications as monitoring seabird nests in remote habitats, pinpointing structural weaknesses in a building after an earthquake, or warning of the presence of biochemical toxins.
"Spec is our first mote to integrate radio frequency communication and custom circuits onto a chip that runs the TinyOS operating system," said Kris Pister, professor of electrical engineering and computer sciences and the pioneer behind the smart dust project. "It's a major step towards sensors that cost less than a dollar a piece and that are integrated into the products that we own, the buildings that we live and work in, and the freeways we drive on. The potential for such sensor networks is enormous."
The Spec mote brings together years of Smart Dust and TinyOS research led by Pister and David Culler, professor of computer sciences. While Pister led research into miniaturizing the hardware components for Smart Dust, Culler and his research team developed the TinyOS operating system that allows the mini-motes to communicate with one another. Their work led to generations of wireless sensor motes slightly bigger than pocket change. But the breakthrough came when Jason Hill, a former graduate student who worked with Culler on TinyOS and Pister, successfully integrated the hardware and software components onto a silicon chip small enough to fit under the wings of the eagle on the back of a quarter.
What is remarkable about Spec is the range of components the UC Berkeley researchers were able to fit onto a single chip and its system-driven architecture. Spec combines a micro-radio, an analog-to-digital converter, a temperature sensor, and the TinyOS operating system onto a piece of silicon 2 by 2.5 millimeters square.
"This is the first fully integrated and fully operational mote on an individual chip, and its design is driven by the networking and system requirements," said Culler. "Single chip integration makes the mote very cheap because it reduces post-assembly requirements. This opens the path to very low cost deployments of a large number of motes."
Researchers tested the new chip at the Intel Research Laboratory in Berkeley. Spec was able to transmit radio signals at 902 megahertz over 40 ft at 19200 kilobytes per second. "We were in a lab environment with a lot of high-power equipment that generates interference," said Hill, who received his PhD in electrical engineering and computer sciences from UC Berkeley in May. "If we went outdoors and had direct line of sight between the two motes, we could realistically transmit about twice the distance we did indoors."
Hill said a drastic reduction in power consumption of components allowed the sensor mote to be shrunk down. Spec includes special hardware accelerators to help the core pieces of TinyOS run more efficiently. For example, the accelerators allowed data encryption to be performed by the hardware, which is thousands of times more efficient than performing the same function in software. In addition, the radio transmitter uses 1,000 times less power than a cell phone.