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updated 3/14/2011 2:10:33 PM ET 2011-03-14T18:10:33

A new study has found a way to implement wireless monitoring technology in buildings – with uses ranging from climate control to health and safety applications – by tapping into heating, ventilating and air-conditioning (HVAC) ducts.

Rather than running wires all through an office or factory to hook up thermometers, say, the study shows how radio waves could be sent through ductwork to power many tiny wireless sensors.

The research opens the door to inexpensively setting up building-wide sensing systems. These systems could include smoke detectors, carbon-monoxide monitors, or sensors that can detect chemical, biological or radiological agents.

Little receivers and transmitters

At the heart of the system are radio-frequency identification (RFID) tags equipped with sensors.

These relatively small, lightweight tags equipped with radio antennas can transmit important information about the inside of a building such as temperature back to a "reader."

In an RFID system, an electronic reader broadcasts a radio wave with a specific frequency. The RFID tags receive the transmission and absorb energy from it, enabling the tag to respond to the reader by the way that it reflects the wave.

Extending the sensor sweep

The researchers focused on ultrahigh-frequency (UHF) RFID systems, which operate in the 902-928 megahertz band in North America (and on various other bandwidths in other parts of the world).

When placed in open spaces, UHF RFID tags typically need to be within 16.5 to 32.8 feet (five to 10 meters) of the reader in order to respond to a transmission.

However, the researchers have found that, by employing a building's HVAC system, UHF RFID tags can operate when located one hundred feet (30 meters) or more from a reader.

The HVAC ductwork is an excellent conduit for the radio transmissions because the ducts typically consist of hollow metal pipes. Those pipes can be used to guide the radio waves, keeping the waves from dispersing, and helping to maintain a strong signal over a greater distance.

"This would work with anything you can create an electronic sensor for," said Dan Stancil, co-author of the study in the September issue of Proceedings of the IEEE and professor and head of North Carolina State University's department of electrical and computer engineering.

Monitoring on the cheap

Today's climate-control units have thermometers placed throughout a building, each of which is connected to a central climate-control monitor via extensive wiring.

In place of all this behind-the-wall spaghetti, one could distribute RFID tags with temperature sensors throughout the building, with short antennas connecting them to the building’s HVAC ductwork. The tags would then send temperature data wirelessly to readers via the ductwork to inform air conditioning and heating systems.

The finding could lead to significant time and cost savings for builders and building managers, since the systems can be put into place without the expense and effort of running wires throughout a structure.

"Because you can tap into existing infrastructure, I think this technology is immediately economically viable," Stancil said.

"Avoiding the labor involved with installing traditional sensors and the related wiring would likely more than compensate for the cost of the RFID tags and readers."

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