MIT engineers configure RFID tags to work as sensors



Platform may enable continuous, low-cost, reliable devices that detect chemicals in the environment.

These days, many retailers and manufacturers are tracking their products using RFID, or radio-frequency identification tags. Often, these tags come in the form of paper-based labels outfitted with a simple antenna and memory chip. When slapped on a milk carton or jacket collar, RFID tags act as smart signatures, transmitting information to a radio-frequency reader about the identity, state, or location of a given product.

In addition to keeping tabs on products throughout a supply chain, RFID tags are used to trace everything from casino chips and cattle to amusement park visitors and marathon runners.

The Auto-ID Lab at MIT has long been at the forefront of developing RFID technology. Now engineers in this group are flipping the technology toward a new function: sensing. They have developed a new ultra-high-frequency, or UHF, RFID tag-sensor configuration that senses spikes in glucose and wirelessly transmits this information. In the future, the team plans to tailor the tag to sense chemicals and gases in the environment, such as carbon monoxide.

“People are looking toward more applications like sensing to get more value out of the existing RFID infrastructure,” says Sai Nithin Reddy Kantareddy, a graduate student in MIT’s Department of Mechanical Engineering. “Imagine creating thousands of these inexpensive RFID tag sensors which you can just slap onto the walls of an infrastructure or the surrounding objects to detect common gases like carbon monoxide or ammonia, without needing an additional battery. You could deploy these cheaply, over a huge network.”

Kantareddy developed the sensor with Rahul Bhattacharya, a research scientist in the group, and Sanjay Sarma, the Fred Fort Flowers and Daniel Fort Flowers Professor of Mechanical Engineering and vice president of open learning at MIT. The researchers presented their design at the IEEE International Conference on RFID, and their results appear online this week.

“RFID is the cheapest, lowest-power RF communication protocol out there,” Sarma says. “When generic RFID chips can be deployed to sense the real world through tricks in the tag, true pervasive sensing can become reality.”


how’s technology 

Recently, researchers have been experimenting with ways to turn passive RFID tags into sensors that can operate over long stretches of time without the need for batteries or replacements. These efforts have typically focused on manipulating a tag’s antenna, engineering it in such a way that its electrical properties change in response to certain stimuli in the environment. As a result, an antenna should reflect radio waves back to a reader at a characteristically different frequency or signal-strength, indicating that a certain stimuli has been detected.

For instance, Sarma’s group previously designed an RFID tag-antenna that changes the way it transmits radio waves in response to moisture content in the soil. The team also fabricated an antenna to sense signs of anemia in blood flowing across an RFID tag.

But Kantareddy says there are drawbacks to such antenna-centric designs, the main one being “multipath interference,” a confounding effect in which radio waves, even from a single source such as an RFID reader or antenna, can reflect off multiple surfaces.

“Depending on the environment, radio waves are reflecting off walls and objects before they reflect off the tag, which interferes and creates noise,” Kantareddy says. “With antenna-based sensors, there’s more chance you’ll get false positives or negatives, meaning a sensor will tell you it sensed something even if it didn’t, because it’s affected by the interference of the radio fields. So it makes antenna-based sensing a little less reliable.”