Smart Dust: Communicating with a Cubic-Millimeter Computer

D ecreasing computing device size, increased connectivity, and enhanced interaction with the physical world have characterized com-puting's history. Recently, the popularity of small computing devices, such as handheld computers and cell phones, burgeoning Internet growth, and the diminishing size and cost of sensors— especially transistors—have accelerated these trends. The emergence of small computing elements, with sporadic connectivity and increased interaction with the environment, provides enriched opportunities to reshape interactions between people and computers and spur ubiquitous computing research. 1 The Smart Dust project 2 is exploring whether an autonomous sensing, computing, and communication system can be packed into a cubic-millimeter mote (a small particle or speck) to form the basis of integrated, massively distributed sensor networks. Although we've chosen a somewhat arbitrary size for our sensor systems , exploring microfabrication technology's limitations is our fundamental goal. Because of its discrete size, substantial functionality, connectivity, and anticipated low cost, Smart Dust will facilitate innovative methods of interacting with the environment, providing more information from more places less intrusively. We use Smart Dust to pursue projects such as • deploying defense networks rapidly by unmanned aerial vehicles or artillery; • monitoring rotating-compression-blade high-cycle fatigue; • tracking the movements of birds, small animals, and insects; • monitoring environmental conditions that affect crops and livestock; • building virtual keyboards; • managing inventory control; • monitoring product quality; • constructing smart-office spaces; and • providing interfaces for the disabled. Smart Dust requires both evolutionary and revolutionary advances in miniaturization, integration, and energy management. Designers can use microelectro-mechanical systems (MEMS) to build small sensors, optical communication components, and power supplies , whereas microelectronics provides increasing functionality in smaller areas, with lower energy consumption. Figure 1 shows the conceptual diagram of a Smart Dust mote. The power system consists of a thick-film battery, a solar cell with a charge-integrating capacitor for periods of darkness, or both. Depending on its objective, the design integrates various sensors, including light, temperature, vibration, magnetic field, acoustic, and wind shear, onto the mote. An integrated circuit provides sensor-signal processing , communication, control, data storage, and energy management. A photodiode allows optical data reception. We are presently exploring two transmission schemes: passive transmission using a corner-cube retroreflector, and active transmission using a laser diode and steerable mirrors. The mote's minuscule size makes energy management a key component. Current battery and capacitor technology stores approximately 1 joule per cubic mm The Smart Dust project …