In recent years, more and more retailers and manufacturers have chosen to use RFID (Radio Frequency Identification Chip) to track their products. Usually these RFIDs are based on a paper label plus a simple antenna and memory chip. When these RFID tags are attached to milk cartons or jackets, they can be used as smart tags to send information such as the identity, status, or location of related products to the radio frequency reader.
In addition to marking products throughout the supply chain, RFID tags are also widely used to track various scenes from casino chips and cattle on ranches, to tourists in amusement parks and marathon runners.
The Auto-ID laboratory of MIT (Massachusetts Institute of Technology) has been at the forefront of RFID technology development. According to a report by Maims Consulting, researchers in the laboratory are now trying to develop a new function for RFID technology: perception. They developed a new ultra-high frequency (UHF) RFID tag sensor that can sense peak glucose and wirelessly transmit signals. In the future, the team plans to improve this RFID sensor to monitor compounds and gases in the environment (such as nitric oxide CO).
"People want to extract more value from the existing RFID infrastructure and expand more applications, such as sensing," said Sai Nithin Reddy Kantareddy, a graduate student in the School of Mechanical Engineering at MIT. "We can build thousands of these at very low prices. RFID tag sensors, attach them to building walls or various objects, and can detect various common gases in the environment, such as carbon monoxide or ammonia, without additional batteries. And create a huge sensor at a very low cost The internet."
Kantareddy’s research team includes scientist Rahul Bhattacharya, as well as Professors Fred Fort Flowers and Daniel Fort Flowers of the Mechanical Engineering Department of MIT and Sanjay Sarma, Vice Chair of Open Learning.
"RFID is currently the cheapest and lowest power RF communication protocol," Sarma said. "When general-purpose RFID chips can perceive the real world by improving tags, then the true sense of ubiquity will become a reality. "
ClutterCurrently, RFID tags have a variety of configurations to choose from, including battery-powered and passive. Both types of RFID tags contain a small antenna that communicates with a remote reader through backscattering RF signals, and sends data or simple codes stored on a small integrated chip in the tag to the latter. Battery-powered tags include a small battery that powers the chip. The passive RFID tag collects energy from the reader itself, and the reader emits radio waves with just the right energy within the FCC limit to provide energy for the storage chip and reflected signal reception in the RFID tag.
In recent years, researchers have begun experimenting with various methods to transform passive RFID tags into long-term sensors that do not require batteries or replacement. These efforts usually focus on the design and modification of tag antennas so that their electrical performance changes in response to certain environmental stimuli. Therefore, when a certain stimulus is detected, the antenna will reflect radio waves back to the reader with different characteristic frequencies or signal strengths.
For example, Sarma's team previously designed an RFID tag antenna that can respond to the humidity in the soil and change the emission of radio waves. The team also built an antenna that can sense the anemia of the blood flowing through the RFID tag.
However, Kantareddy claims that this type of antenna-centric design has many flaws, the main one being "multi-channel interference"-even radio waves from a single source (such as an RFID reader or antenna) will be in multiple Reflect on the surface, thereby bringing confounding effects.
"According to environmental conditions, radio waves will be reflected multiple times on walls and objects before being reflected back to the tag, which will interfere and cause noise," Kantareddy said. "With antenna-based sensors, there is a higher chance of incorrect determinations. Or negate the signal, which means that the response of the sensor may not be accurate because it will be interfered by the radio field. Therefore, the antenna-based sensing lacks sufficient reliability."
Small changes, great wisdomSarma's team adopted a new solution: instead of targeting the tag antenna, it tried to improve its memory chip. They purchased a commercially available integrated chip that can switch between two power supply modes: one is a mode based on RF energy, similar to a fully passive RFID; the other is a local energy assist mode, such as using an external battery or capacitor, similar For semi-passive RFID tags.
The research team used a standard radio frequency antenna and the chip to embed the RFID tag. In a key step, the researchers made a simple circuit around the memory chip, and when the chip perceives a certain environmental stimulus, it can switch the chip to local energy assist mode. In this mode (Battery-Assisted Passive Mode, BAP), its chip will transmit a new protocol code, which is different from the conventional code it transmits in passive mode. Then, the reader translates this new code, indicating that the RFID tag has detected the environmental stimulus of interest.
Kantareddy said that the RFID sensor based on chip design is more reliable than the sensor based on antenna design, because it fundamentally distinguishes the tag's sensing and communication functions. In antenna-based sensors, the chip that stores data and the antenna that transmits data both rely on radio waves reflected in the environment. In Kantareddy's new design, its chip does not need to rely on mixed radio waves to achieve sensing.
"We hope that the reliability of the data can be improved," Kantareddy said. "As long as it is in the sensing state, our new solution will emit a new protocol code with enhanced signal, so that the sensing state and non-sensing state of the tag can be clearly judged. ."
"This solution is very interesting because it also solves the problem of information overload caused by a large number of tags in the environment," Bhattacharyya said. "This solution abandons the continuous analysis of information flow through short-distance passive tags and enables RFID readers. It can be placed far enough to communicate and handle only important events."
Plug-and-play sensorAs a demonstration, the research team developed an RFID blood glucose sensor. They use commercially available glucose sensing electrodes, which are filled with the electrolyte glucose oxidase. When the electrolyte interacts with glucose, the electrode generates an electric charge, acting as a local energy source or battery.
The researchers connected these electrodes to the memory chip and circuit of the RFID tag. When they add glucose to each electrode, the charge generated can switch the chip from its passive RF power mode to a local charge assist mode. The more glucose is added, the longer the chip will be in the second power mode.
Kantareddy said that a reader capable of sensing this new power mode can use this as a signal of the presence of glucose in the environment. This reader can determine the glucose content by measuring the time the chip is in battery-assisted mode-the longer the time in this mode, the higher the glucose content.
Although the sensor developed by the research team can detect glucose, its performance is still lower than that of commercially available dedicated glucose sensors. Kantareddy stated that their goal is not to develop an RFID glucose sensor, but to show that their design is compared to antenna-based The sensor is more reliable.
"With our design, the data obtained is more reliable," Kantareddy said.
In addition, their design is more efficient. The tag can use the RF energy reflected nearby to operate in a passive mode until the environmental stimulus of interest appears nearby. The stimulus itself can provide power to the tag and send an alert code to the reader. Therefore, the sensor itself can provide additional energy for the integrated chip.
"Because this tag can obtain energy from both radio frequency and electrodes, its communication range has been greatly expanded," Kantareddy said. "With this design, the distance of the reader can reach more than 10 meters, far more than It's 1~2 meters away. Therefore, the same area can greatly reduce the number and cost of readers."
Next, he plans to develop an RFID carbon monoxide sensor by combining its design with different types of electrodes. When carbon monoxide appears, the sensor can generate electrical charges to power it.
"Using an antenna-based design scheme requires designing a specific antenna for a specific application," Kantareddy said. "With our design scheme, you only need to choose to use commercially available electrodes, plug and play, which makes the entire design concept Very easy to expand. Users can deploy thousands of these sensors at home or in the factory to monitor boilers, gas storage tanks or pipelines."
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