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Techniques Boost Range, Accuracy of Wireless ID Signals

Sabesan Sithamparanathan

Sabesan Sithamparanathan (Girton College, University of Cambridge)

Engineers at University of Cambridge in the U.K. developed techniques to vastly improve the range and accuracy of passive radio-frequency identification (RFID) tags used to identify passports, luggage, and goods in transit. The team led by Cambridge research fellow Sabesan Sithamparanathan published its findings online in the journal IEEE Transactions on Antennas and Propagation (paid subscription required).

RFID systems have a reader and tag with an identifier, similar to a bar code, that use radio signals to transmit the identifier to the reader.  Passive RFID tags are coded with data, but have no built-in power source, such as a battery. The tags draw their power from the reader and are less expensive than active tags with their own power. As a result, however, passive tags are limited in the data they can store and the range over which they can be detected.

The Cambridge team addressed these and other limitations of current passive RFID tags. “Tag detection accuracy usually degrades at a distance of about two to three meters,” says Sithamparanathan in a university statement, “and interrogating signals can be cancelled due to reflections, leading to dead spots within the radio environment.”

The researchers adapted a distributed antenna system like the kind used to improve wireless broadband signals in a building. Distributing the antennas made it possible to dynamically move the dead spots by adjusting the phase and frequency of the signals transmitted from the multiple antennas.

The demonstration system built by Sithamparanathan and colleagues was able to accurately read signals in a 15 by 20 meter area. The team also reports the system’s accuracy improved to nearly 100 percent, compared to 50 percent or less with conventional passive RFID systems. In addition, the researchers were able to limit the number of additional antennas required, thus limiting its eventual cost.

The researchers plan to commercialize the system, which has already received recognition in entrepreneurial competitions in the U.K. An earlier version of the system received the Royal Academy of Engineering ERA Foundation Entrepreneurship Award for 2011. The prize included £30,000 ($US 49,700 today) to invest in the system’s development.

Among further enhancements planned for the system is a tag-finding capability, to not only read the tag over a larger area, but also pinpoint its location.

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