A research team at North Carolina State University has used a building ventilation duct to at least triple the normal distance that radio waves emitted from passive RFID tags can travel over open space.

The discovery means that a small, inexpensive RFID tag could be used to wirelessly transmit data from any temperature sensor, smoke detector, carbon monoxide monitor or a sensor to detect chemical, biological or radiological agents in a large building, according to Dan Stancil, one of the main researchers and head of the university's Department of Electrical and Computer Engineering.

Stancil told R&D magazine that using the RFID tags with electronic sensors could be "immediately economically viable" because it would mean the wiring and the labour to install the wiring would not be needed to connect a building's various sensors. The research will be published in the September issue of Proceedings of the IEEE, according to a synopsis in R&D Magazine.

The university team found that metal HVAC (Heating, Ventilation and Air Conditioning) ducts act as electromagnetic waveguides to greatly increase the communication range of ultra-high frequency (UHF) radio frequency identification (RFID) tags, when compared to the distance of their propagation over free space. The tags emitted a radio signal picked up by an RFID reader at the other end of a 30-meter piece of duct work, the team found. Most UHF RFID tags typically propagate only 5 to 10 meters over open spaces.

The team studied passive RFID tags, which are activated by a signal from an RFID reader. Active RFID tags, by comparison, regularly emit a signal and must have their own source of power. In North America, UHF RFID systems operate in the 902-948 MHz band.