- The chipless tags consist of sensor material and an antenna to reflect a response to an RF interrogation with a modified frequency
- That change in frequency from the tag response would indicate sensor measurements, such as an increase or drop in temperature
Researchers at the University of Glasgow have developed a system that aims at wireless sensing, without the environmental impact of silicon in RFID tags. They intend the new chip-less RFID technology to support inventory management and conditions tracking in retail, healthcare and smart clothing. When tested in the university’s laboratory, the system demonstrated that tags—minus chips—could be read for applications such as food safety or healthcare applications.
Each tag’s sensor material and coil antenna provide data related to how the RF interrogation is received. The researchers aim to offer a more sustainable alternative to standard UHF RFID technology because they would be easier to recycle, without an IC built in, and require less production processing to make.
The tag consists of inexpensive antenna coils and a sensing material made from PDMS silicon rubber and carbon fibers. The coils, smaller than the ones found in credit cards, absorb electromagnetic signals from a hand-held reader using electromagnetic waves.
Testing found the sensors can detect variations in temperature between 20 and 110 degrees Celsius. The technology, if commercialized, could help make future wireless sensors cheaper as well as more sustainable, the researchers said.
Eliminating Chip Production Process
Standard RFID tags include a chip with a unique ID encoded on it. The chip stores that ID as well as some additional data if necessary. It can be linked to a sensor to collect conditions data such as temperature; however, storing that data would require a battery.
The researchers have been working on their own sustainable electronics method for several years, said Mahmoud Wagih, lecturer at the University of Glasgow’s James Watt School of Engineering, and author of their recently released white paper and article in the Advanced Science journal.
Wagih noted that the tags performed particularly well between 20 to 60 degrees Celsius, the range most relevant for food safety and medical applications. They are capable of reacting quickly to changes in temperature, taking just seconds to register significant changes, said Benjamin King, university of Glasgow’s research associate. So if the temperature was changing while the tag was being interrogated, that change would be reflected in the response.
Taking Advantage of Convenience of RFID
The researchers opted to develop an RFID-based system, “because of the convenience of UHF RFID,” said Wagih. He pointed to the fact that “the retail type style [RFID tags] being available everywhere,” especially on garments, for inventory tracking. Companies are accustomed to interrogating tag to learn details about products in stores or in the supply chain.
The Glasgow team was seeking a way to limit the carbon footprint of such tags which would require the related etching and chemical waste of making chips. “The chip is the most complicated bit to manufacture, so if you wanted to bring the cost and environmental impact down you would want to eliminate the chip,” Wagih said.
In fact, the carbon impact of a standard UHF RFID tag is about 50 percent of the tag’s full impact, said Wagih, based on the production and the recycling of the tag and chip. The chipless version they developed can send only three bits of data related to sensing, as opposed to standard UHF RFID which can be approximately 128 bits or more.
Network Analyzer as Reader
Instead of using a standard RFID reader, the system employs a network analyzer—an RF-based measurement device often used in laboratories which can be purchased at relatively low cost. The analyzer takes a wide band approach. While standard UHF RFID transmits at 900 MHz, the analyzer can transmit in that range and receive responses across about 50 MHz in that bandwidth.
The material in the tag is modified by temperature changes. When it receives an interrogation signal from the antenna, it can respond. But depending on the temperature, it will shift the frequency in its response.
When using the analyzers, said Wagih, “we’re reading the change in the properties of the tag—so the frequency shifts slightly depending on the temperature.”
Food Packaging
The chipless tag could be built into food packaging or applied to goods during manufacturing to track conditions during or follow production. “If the frequency you’re measuring, for example, falls outside of a given range that could tell—‘we’re not operating at the conditions that we want’,” King said.
The tags could also be used in stores on shelves where an analyzer could be deployed to track conditions for products displayed there. The analyzer could be installed under each package and continuously read conditions the product is exposed to on a store shelf.
“If for example one region in that shelf is now overheating, or something is not cooling in one part of the fridge” that data could be acted upon in real time, said King.
Currently, the reader can interrogate three tags at once with the target to increase the reading capacity to10 tags at once.
Without a unique identification of the tag, the goal is not to know specifically which tag responded with a temperature change but the fact that one did. The system currently works only at very short range—about one centimeter. Therefore, users would commonly be looking directly at the tagged item that provided the specific response.
The sensing material can be designed to respond to specific conditions beyond temperature, King added. “That sensing material, its properties change in response to whatever stimuli that we have in mind so there’s really nothing stopping us from being able to design a humidity sensitive material or pressure sensitive material — the potential versatility is interesting.”
Wearable Device for Health Tracking
The tags provide potential for wearable devices as well, by detecting changes in a person’s temperature, or breathing rate or even heart rate. The team envisions that the reader could be integrated into a mobile device like a phone to make it easier to access sensor data.
Additionally, in agriculture sensor probes the technology could be detecting and transmitting changes in soil conditions whether the condition being tracked is the temperature, or pH level or moisture.
The researchers are aiming for a solution that would be low impact related to the recycling or disposal process. Currently RFID tags can be a challenge to recycle because the chip is not recyclable and would need to be separated from the tag. The sensing material could be reused on another product, Wagih said, “so it simplifies recycling.”
The next goal is to scale up the capabilities of the tag to accomplish other sensing functions.