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RFID Testbed Measures Multiple Tags At Once

ATLANTA, GAResearchers have designed a system that is capable of simultaneously measuring hundreds of radio-frequencyidentification (RFID) tags and rapidly testing new RFID-tag prototypes. According to Gregory Durgin, an assistant professor at the Georgia Institute of Technology's School of Electrical and Computer Engineering, "This testbed allows us to measure the signal strength of tags hidden behind other tags and to rapidly test unique antenna and multiple antennas without actually constructing new tags for each experiment." The research, which was funded by the National Science Foundation and conducted with former graduate student Anil Rohatgi and current graduate student Joshua Griffin, was presented at the IEEE International Conference on RFID.

RFID tags are used for applications that include inventory management, package tracking, toll collection, passport identification, and airport luggage security. Passive tags include an integrated circuit (IC) for storing and processing information and an antenna that responds to radio waves transmitted from an RFID reader. The tag absorbs some of the RF energy from the reader signal and reflects it back as a return signal delivering information from the tag's memorya technique called backscatter.

If several RFID tags are in the vicinity of a reader, the reader usually communicates with the tag transmitting the most powerful signal first. It puts it to "sleep" to prevent it from transmitting repeatedly. The reader then moves the next most powerful signal and so on. According to Durgin, "We designed a really inexpensive, simple anti-collision system that transmits multiple unique signals back to us simultaneously without this complicated back and forth process."

The system includes three parts: a transmitter, receiver, and emulator. The emulator simulates the activity of an IC. The transmitter sends a radio signal to the antenna. By attaching the emulator to an antenna, a unique spread-spectrum signal is transmitted to the receiver. Each antenna signal can then be separated from the others, allowing the team to simultaneously measure the signals from multiple tags. The experiments have shown that they can measure the power strength and phase of up to 256 antennas in the field of view, which is an area in front of the reader of approximately 20 by 20 feet.

It is important to test multiple configurations because RFID readability and antenna power strength can be affected by the relative position and orientation of the tag antenna and reader. The testbed was designed for measurements at 915 MHza common ultra-high frequency for backscatter RFID applications. The system is being expanded to test antennas at higher frequencies up to 5.7 GHz.

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