Where Sensors Make Sense

Siemens aims to turn your thermostat into a "comfortstat" -- and create a viable market for wireless sensor networks.

The idea of tiny, ubiquitous computers monitoring us and our environments from every nook and cranny might alarm a few civil libertarians -- but this is exactly the concept driving researchers who are trying to perfect networks of smart, wireless sensors.

They envision sensors sprinkled across a battlefield to warn of an enemy advance, or attached to pill bottles to alert caregivers to when an elderly patient takes (or doesn't take) his or her medication. They imagine faulty equipment in manufacturing plants that reports its own failures. In short, they see a pervasive grid of smart sensors that monitor, analyze, and network the bits and bytes of life.

For years, these networks have remained largely in the prototype stage, not quite ready to hit the market. "We know that it is a good concept; we've demonstrated its feasibility," says Osman Ahmed, senior principal engineer at Siemens Building Technologies in Buffalo Grove, IL. The problem, Ahmed explains, is that no major company has yet found a compelling commercial market for sensor networks.

Research groups at Intel and the University of California's Berkeley and Los Angeles campuses continue to experiment with research prototypes. Small companies, such as Sensoria in San Diego and Ember in Boston, have pushed the technology forward, but have yet to break through with a killer app.

Siemens, however, has developed a new type of sensor that can detect multiple types of environmental changes and is mass-producible. And the company is studying which sensor network applications will appeal to customers first.

In most sensor networks, each node includes an individual sensor that detects one of several parameters such as temperature, humidity, vibration, or the presence and concentration of a chemical. The sensor is coupled to a microprocessor that stores and processes information and a radio that transmits data. These nodes are dispersed throughout an environment, such as city sewer lines or building spaces, and communicate via a "mesh network" in which information hops from node to node, en route to a centralized hub.

What makes Siemens' devices a breakthrough is that six different sensors can be fabricated on one chip, layered on top of each other, "like a sandwich," says Ahmed. Each layer is made of a material that's specialized for reading a different environmental element. For instance, when carbon monoxide molecules land on the layer that's sensitive to it, the electrical properties of that layer change with the concentration of the gas. This electrical information is transmitted to the microprocessor, then relayed to the network's central hub.

By streamlining the fabrication process and putting six sensors on one chip, Siemens has reduced production costs to a sixth of the former cost, says Ahmed.