New RFID Tags Configured as Sensors Can Detect Carbon Monoxide Levels—and the Sweetness of Wine
Using electrolyte glucose-oxidase as a battery source, MIT researchers have configured RFID tags as sensors, which improves the signal-to-noise ratio and reduces multipath issues.
Researchers in the Auto-ID lab at MIT have developed a new medium-activated RFID sensor technology, which they say is versatile, cost-effective, and scalable.
Conceptual implementation of RFID sensors providing various measurements in an outdoor environment. Image used courtesy of Chelsea Turner, MIT
This new technology may solve many of the problems associated with previous passive RFID sensor designs, namely detecting material change with specific antenna design and overcoming multipath signal fade during transmission between RFID chip and reader.
Traditional Antenna Design and Passive RFID Chip Signal Fade
The technology has been developed by a three-member team: Sai Nithin Reddy Kantareddy, a graduate student in MIT’s department of mechanical engineering; 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 team overcame the antenna design issue by focusing on changing the state of the memory circuitry instead of the antenna topology, making detection an independent feature. They split the state of the sensor from the transmission capabilities.
“With antenna-based designs, you have to design specific antennas for specific applications,” Kantareddy says. "With ours, you can deploy hundreds or thousands, in your house, or in a facility where you could monitor boilers, gas containers, or pipes.”
The Medium is the Message
With these RFID tags reconfigured as sensors, perhaps the “medium is the message.” Although in this case, it’s also the function that solves multipath challenges. The team at MIT has taken the medium (the electrolyte glucose-oxidase, in this case) and used it to power the memory circuits changing its state, extending the range of the message.
Multipath signal fade causes destructive signal loss when multiple copies of a signal reach the receiver out of phase. Image used courtesy of Firas Mohammed Ali Al-Raie
The team has taken commercially-available electrodes and re-purposed them for use with the new RFID circuit. These electrodes generate current in the presence of a particular gas, and the team successfully extended the range of an RFID chip “from 1 to 2 meter… to more than 10 meters.”
There are many electrodes designed for this purpose—for example, glucose sensors, which are a type of electrical transducer called an amperometric sensor. When using the medium as a battery source, the RFID sensor has more power available to the antenna, improving the signal-to-noise ratio and reducing multipath issues.
Battery-Assisted Passive Mode: A “Sense-Able” Option?
The battery-assisted passive mode (BAP) is a positive logic state, or “active-high.” However, these new RFID chips can also be used in a negative logic or “active-low” state, where the chip reader is no longer detecting the presence of the BAP sensor profile because the electrical charge generated by the electrodes has diminished.
Some companies, like Powercast, do offer "RFID sensor tags" that monitor environmental conditions. Image used courtesy of Powercast
This provides systems designers with two states with which to design industrial controls.
Sensing Carbon Monoxide—And the Sweetness of Wine
The team at MIT reports wireless glucose detection in the 5-30% range, making it useful for detecting residual sugar concentration, indicating when your wine is just sweet enough. This new technology can be applied at scale to monitor the fermentation process of a winery remotely; think an RFID chip to a reader to an IoT device such as your cellphone. As the sugars in the wine are broken down by the yeast, the RFID will enter into passive mode, alerting the RFID reader to a threshold change in glucose concentration.
The device can also be used to ensure ongoing health and safety during changing work conditions, such as the hazard of carbon monoxide poisoning in enclosed workspaces. Rising carbon monoxide (CO) levels in your working environment cannot be detected without sensor technology.
Kantareddy is actively working to develop an RFID sensor capable of detecting the presence of CO in the local environment. Automation and control can take advantage of this approach to disable CO-generating equipment or automatically vent a poisoned atmosphere from an enclosed space.
Whether you are measuring sugar content in wine or ensuring that enclosed spaces are safe for work, RFID sensors provide a cost-effective sensor technology that can be scaled together to create a wireless network for industrial controls’ decision making.
Do you work with RFID tags? What advantages or limitations do you see in this design model? Share your experiences in the comments below.