Lightweight Relays Enable Small Drones to Read RFID Tags Indoors

By Claire Swedberg

MIT has developed an RFID system that would allow users to capture tag reads with a small drone carrying a virtual antenna array to forward data between tags and a reader.

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In recent years, RFID-enabled drones have been deployed to track inventory and assets in storage yards and other outdoor settings throughout the United States and worldwide. Indoor settings, however, pose some challenges. RFID readers can be heavy enough to require a large drone to carry them, while large drones are not always nimble or safe enough for indoor settings. But there is value in using drones indoors—at large warehouses and distribution centers, for instance—says Fadel Adib, an assistant professor at MIT and a principal investigator at MIT Media Lab.

For that reason, the MIT Media Lab had developed a UHF RFID tag-reading system known as RFly that keeps the RFID reader on the ground, while deploying relays to capture the reader’s RF signal, forward it to tags and send responses from those tags back to the reader. The system enables small, lightweight drones to operate in a large environment, flying over tagged items to capture ID numbers and approximate the tags’ locations within about a foot.

MIT researchers have developed a system that enables small, safe, aerial drones to read RFID tags in large warehouses at a distance of several meters.

With the development of RFly, Adib says, researchers sought an alternative to manual inventory-tracking processes by personnel in large warehouses. They first explored the basic technologies available. A drone could carry a bar-code scanner, but bar codes require a line of sight. A similar problem makes camera-based drones unrealistic, since stacked inventory would put some items out of a drone’s view.

According to Adib, the MIT team attached an off-the-shelf UHF RFID reader onto a small drone, which crashed. A large drone would pose safety problems, he says. If an individual were working or dwelling in an indoor setting and were to be hit by a large drone, an injury could result. A smaller drone, on the other hand, would likely cause little damage.

Since the small drone could not support the RFID reader, the group needed to develop a different strategy. Adib says they considered using a relay that would act as a repeater. The relay, with a built-in RFID antenna, can receive a signal from the reader, then use the power from that signal, as well as the drone’s built-in battery, to forward an interrogating signal that is received by passive RFID tags within its vicinity. (The relay consumes less than three percent of the drone’s battery altogether, they found.) The tags respond, and the relay captures their IDs and forwards that information to the reader.

This helps the reader software to approximate each tag’s location based on the angle at which its ID is received as the drone is moving, using algorithms to determine where the tag is situated, according to the drone’s location and the angle of RF response. The group refers to this technology as a virtual antenna array on the drone. Such a setup is a favorable alternative to received signal strength indication (RSSI), Adib says, since RSSI calculations can be disturbed in indoor environments by reflections around the tag and reader.

The Media Lab has tested the drone at its own lab, and found that it can read tags accurately across about 100 times the coverage area of a simple RFID reader-and-tag scenario. It further tested the technology at furniture retailer Red Thread‘s warehouse, in Boston, for the stability and safety of the airborne technology in a real-world environment.

Fadel Adib

The drone that the researchers are using measures 30 centimeters by 40 centimeters (11.8 inches by 15.7 inches) and can carry a device weighing up to 200 grams (7 ounces). Because the relay weighs only 30 grams (1 ounce), Adib says, the system could work on an even smaller drone.

The group’s next step is to further develop the system to capture more granular accuracy data. The goal, according to Adib, is to pinpoint a tag’s location within half an inch. This level of granularity may become increasingly important, he notes. “In the future,” Adib states, “you may need robots to fetch an item, and that level of accuracy would be necessary” to ensure that the robot collects the right goods.

How such granular location accuracy will be accomplished has not yet been decided, Adib says. In the long term, he adds, the group plans to work with partner companies that may wish to help develop a full solution for commercial customers.