Volume 3, Issue 3 April 2003

2003
2002
2001

A Big Radio in a (Very) Small Package by David Pescovitz Printer-friendly version The single-chip Mote measures approximately 2mm x 2.5mm. Courtesy Al Molnar Graduate student Al Molnar's circuit design skills may have landed him a world record, or at least the respect of radio frequency researchers around the globe. The PhD candidate in the Department of Electrical Engineering and Computer Sciences recently devised a transceiver-on-a-chip that's 50 times smaller than a cell phone, consumes 1,000 times less power, yet operates at the same frequency. Molnar's micro-radio is a key ingredient in the latest iteration of UC Berkeley's Smart Dust, a research project in the Center for Information Technology Research in the Interest of Society (CITRIS). Invented by Molnar's adviser, Professor Kris Pister, the tiny and inexpensive Smart Dust Motes can be outfitted with sensors for myriad applications — from diagnosing a building's structural integrity to measuring light and temperature for energy use monitoring. Graduate student Al Molnar spent two years in industry designing radios for mobile phones. Courtesy Al Molnar Outfitted with their own TinyOS operating system, the motes self-organize into ad hoc wireless networks and pass their data from one to another bucket-brigade style until the information reaches a central computer for processing. The previous generation "Mica" Mote, now commercially available through Crossbow Technology Inc., is the size of a matchbox and runs on two AA batteries. In March, members of the Smart Dust research team, including graduate students Jason Hill, Ben Cook, Mike Scott, and Brett Warneke, took a major leap forward in their quest to combine ultra-low power computation, communication, and sensing into a single tiny device. Hill successfully tested his design for a new single-chip "spec" mote that's only five millimeters square and includes a transmitter built by Molnar. Once the spec mote is ready for prime time, Pister says, his new company, Dust Inc., will add the device to its product line. The tiny Spec Mote (center, on top of the large black chip), is dwarfed by the previous generation Mote, the Mica Mote. Courtesy Al Molnar Molnar's research thrust is ensuring that the motes' communication systems are practical from a power perspective. In traditional radios, he explains, transmitting just half a watt could consume as much as three watts. That kind of overhead is simply not acceptable if the motes are to be "thrown out into the world and left alone for a few years," he says. "We want to transmit a few hundred microwatts," Molnar says. "But we want to do it with just a milliwatt. The question is, how do you build a circuit that will operate at the same frequency as a cell phone but cost almost nothing in power overhead?" One solution, he says, is to force the little bit of power that is available to work overtime. A battery in most radios, he explains, may produce a group of three electron volts at a time and devote all of them to one particular task. But in Molnar's design, each component requires far less power, enabling every electron to be sent to several components of the radio before the energy is totally dissipated. Can these powerful micro-radios be used to improve society? We want to hear from you... "Since we're never going to try to produce large signals, all our voltages are small," Molnar says. "Because of that, the amount of energy per operation is less, and you can do more operations with a given amount of power." Breaking up the usage of electrons is just one method Molnar employed to cut down on the power requirements of his radio. He also designed the device so that any remaining energy in the electrons that are sent to the oscillator — the component that creates a wave at a specific wavelength by trading electrical and magnetic energy back and forth — is used to drive other parts of the radio circuit instead of being left to dissipate. "These are all standard tricks," Molnar says. "I've just taken them to new extremes for the Smart Dust platform." Jason Hill's Spec Mote page Smart Dust Dust Inc. CITRIS Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking research underway today at the College of Engineering that will dramatically change our lives tomorrow. Editor, Director of Public Affairs: Teresa Moore Writer, Researcher: David Pescovitz Designer: Robyn Altman Subscribe or send comments to the Engineering Public Affairs Office: lab-notes@coe.berkeley.edu. © 2003 UC Regents. Updated 4/4/03.