Smart Sensors: Invisible, Intelligent, and Enveloping

September 2009
Topics: Sensor Technology, Nanoelectronics
To meet the nation's evolving security needs, sensor systems are being developed to be deployed for a number of applications in a variety of environments.

Smart Dust

Our nation faces many security challenges in this post-9/11 era. We need to enhance the technology of our security screening while still maintaining the brisk flow of commerce; we need to protect our critical infrastructures and assets; and we need to protect our armed forces in the field. A new breed of miniaturized sensors arranged into adaptable, self-organized networks may play a role in achieving these goals and many others.

Such networks of miniaturized sensors were christened "smart dust" by their conceiver, Prof. Kris Pister of the University of California, Berkeley. According to Prof. Michael J. Sailor of the University of California, San Diego, smart dust could be "inconspicuously stuck to paint on a wall or to the side of a truck or dispersed into a cloud of gas to detect toxic chemicals or biological materials. When the dust recognizes what kinds of chemicals or biological agents are present, that information can be read like a series of bar codes by a laser that's similar to a grocery store scanner to tell us if the cloud that's coming toward us is filled with anthrax bacteria or if the tank of drinking water into which we've sprinkled the smart dust is toxic."

Although the concept of smart dust is many years from becoming a reality, researchers are hard at work laying the groundwork for it. In developing such emerging sensor technologies— systems that can be deployed in a variety of challenging environments and for a number of novel applications—researchers are focusing on three key requirements: miniaturization, orthogonal sensor systems, and self-organizing networks.

Miniaturization

The more miniaturized sensors are, the more flexible they become. Miniaturized sensors could be embedded in the walls, ducts, and ventilation systems of buildings or into airplanes, road-side barriers, and railway turnstiles.

Developments in nanotechnology and materials science are making the miniaturization process cheaper and more effective. According to Intel's 2005 study regarding the price trends of smart dust motes, "With reengineering, Moore's Law, and volume production, motes could drop in price to less than 5 dollars each over the next several years." Following this model, Intel projects that a tiny sensor, or mote, will retail for approximately 5 cents by 2020.

Orthogonal Sensor Systems

Although miniaturizing sensors promises a host of benefits, it will be important for researchers to evaluate when they are reaching a point of diminishing returns, especially when it comes to trading performance for size. Miniaturization may exacerbate existing sensor challenges such as high false alarm rates. However, by linking sensors into networks, performance degradation of one sensor element in the network due to miniaturization can often be compensated for by another element in the network. In optimizing the overall measure of effectiveness of the sensor system, this network links individual sensor components in multifaceted ways—for example, in a serial or parallel mode or a combination of both.

Such networks perform best when they combine "orthogonal" sensors—sensors that are tuned to detect different stimuli. If sensors based on only marginally different operating principles are combined, the resulting redundancy in the network may only provide a marginal increase in utility over individual sensors. On the other hand, a system that integrates sensor components based on two completely different physical principles, such as ion mobility spectrometry with laser-induced fluorescence, will provide significantly higher utility and better fidelity in threat detection.

Self-organizing Networks

Sensor networks need to be able to adapt quickly to changes in the mission environment. But sensors often lack the autonomy to respond rapidly to shifts in threat and environment. To supply sensor networks with the necessary agility, researchers are designing self-organizing sensor systems.

For example, a new priority will be added to the sensor network's mission or the network will detect a change in its environment. To respond, the network will need to adapt. Special algorithms will allow the network to alter its sensor selection and reorganize the integration of those sensors. The current state of the art in open systems architecture and plug-and-play operation falls far short of the requirements needed to design self-organizing networks, but developers are beginning to focus on meeting these needs.

The Future of Networks

Ever-changing threats to our society have created an urgent need for emerging sensor technologies that build on the preceding ideas. By integrating its research in chemical, biological, and explosives threat detection with its core expertise in robotics and systems engineering, MITRE has been strengthening its position as an innovator in emerging sensor technology. Based on the current progression of MITRE's own sensor R&D initiatives and that of other organizations, it seems reasonable to believe that the utility, mobility, and cost requirements for advanced sensor networks could be met in the next five to ten years.

—by Samar K. Guharay

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