With almost all modern smartphones featuring RFID readers, RFID tags are becoming more prevalent in our everyday lives, and they can be found on food packaging, anti-theft devices, shipping containers, and everything else in between, but engineers at the Massachusetts Institute of Technology have found a new use for these increasingly more common electrical devices: Cheap chemical sensors.



(Image Credit: Scott Lewis)



Engineers at the Auto-ID Lab at MIT have developed new ultra-high-frequency (UHF) RFID tags that can sense glucose spikes, and then transmit that data wirelessly to a receiver. This will be very handy for diabetics who could one day wear an RFID Sensor-based necklace or bracelet that would inform the wearer when their glucose levels rise, but the team says that the implications for this advancement are much broader than just glucose sensing.  In the future, the technology could be used to sense carbon monoxide, gas leaks, or maybe even smoke.


“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.”


RFID based chemical sensors could cut the cost of these types of sensors drastically, and while there are battery powered versions of RFID Tags, many of the tags operate “passively” meaning that the sensors RFID antenna actually harvest energy from the receiver’s antenna which emits enough energy to power the small RFID tags. The implications of passive chemical sensors that can be read by a common smartphone are massive and could allow sensor deployment in environments where actively powering the sensors might not be possible.


The research efforts have mainly focused on using the RFID tag’s antenna, manipulating it to cause a change in its electrical properties based on the presence of various chemicals in the atmosphere surrounding the tag. The way it works is that the tag reflects radio waves back to the receiver at a different frequency or signal strength based on different chemical compositions or levels in the environment. The team previously demonstrated this by transmitting a different signal based on the moisture content of soil surrounding the sensor.


“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.”


The major breakthrough came when the group began focusing less on the RFID antenna and refocused on the RFID tag’s memory chip. Using an off-the-shelf chip that featured passive, and energy-assisted modes, the team was able to create an RFID tag that would switch the chip to the energy-assisted mode if certain environmental stimuli were present. This is possible because the chip emits a different, and distinct protocol code than when it’s in “passive mode,” which tells the receiver that the specified stimuli is present. This creates a more reliable RFID sensor as it separates the RFID tag’s sensing and communications tasks.


“We hope reliability in the data will increase,” Kantareddy says. “There’s a new protocol code along with the increased signal strength whenever you’re sensing, and there’s less chance for you to confuse when a tag is sensing versus not sensing.”


“This approach is interesting because it also solves the problem of information overload that can be associated with large numbers of tags in the environment,” group member and research scientist Rahul Bhattacharya says. “Instead of constantly having to parse through streams of information from short-range passive tags, an RFID reader can be placed far enough away so that only events of significance are communicated and need to be processed.”


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 month.


If you would like to learn more about the group’s research, you can find their recently published paper at this link.


Source: MIT News