New Testbed Promises to Hasten RFID Tag Development

"By sending a low-frequency data waveform to the PIN diode, we can control what signal it scatters back," Durgin says. "This waveform is generated by a computer and fed by a set of thin wires or—in a future version—an infrared link. The PIN diode is driven by this signal and can emulate the full complement of loads that a real RF IC experiences during its signaling. Electrically, the emulator and the RF IC are identical."

In addition, because each tag signal can be separated from the others, testers can simultaneously measure signals from multiple tags. One of the testbed's developers, former Georgia Tech graduate student Anil Rohatgi, showed in his master's thesis work that the testbed can measure the power strength and phase of up to 256 RFID tag emulator/antennas in the receiver's field of view, an area approximately 20 feet in length, width and height.

"Each RF tag gets a uniquely coded spread-spectrum sequence," Durgin says. "Although the receiver hears a cacophony of tags scattering back information, through signal processing we can filter out the unique codes and simultaneously measure the amplitude and signal phase of up to 256 RF tags in the same field of view. This is a scenario that makes industry RFID readers choke."

The testbed is available now, and Durgin says he and his colleagues have already collaborated with Virginia-based Luna Innovations Inc. and several other companies involved in specialty RFID antennas and system measurements. "We recently finished a project with a company that was retrofitting an RFID tag with passive corrosion-sensing capability," he notes. "It was a neat idea that could only be evaluated on our testbed, because of the non-standard antenna designs they were using."

The research and development of the new testbed, funded by the National Science Foundation (NSF), was led by Durgin, Rohatgi and Joshua Griffin, currently a graduate student at Georgia Tech. The system was presented in April at the IEEE International Conference on RFID in Las Vegas.

Work first began on the testbed about five years ago, Durgin says. "We invented a simple testbed," he states, "and at that time, we were simply interested in a way to test how the performance of 915 MHz RFID antennas changed when they were attached to different objects, such as wood, plastic, metal, liquid containers, etc. Since then, we have kept adding functionality and are currently in the middle of a five-year NSF project for developing new 5.7 GHz backscatter systems. No commercial technology operates this high in the microwave band, but there will be in a few years."

The testing of RFID tags that operate at frequencies other than 915 MHz and 5.7 GHz is also a possibility. According to Durgin, several companies interested in experimenting with various kinds of new RFID sensors and multiple RF frequencies have contacted the university.