Reused RFID tags allow battery-free sensing and tracking

Data is power. According to Dinesh Bharadia, an associate professor at UC San Diego in the Department of Electrical and Computer Engineering with an affiliate appointment in the Department of Computer Science and Engineering and the Qualcomm Institute (QI), “Data will be the ‘silicon’ of the next decade.” “”

the The rapid growth of the Internet of Things It means that data is more readily available and accessible than ever before. Sensors, “smart” devices and software are connecting our world to the cloud, collecting information and enabling new types of data sharing and analysis. However, most of these gadgets are battery-powered and have difficulty sensing changes in real-time.

Now the tide is starting to turn.

New research presented and published in Proceedings of the 22nd ACM Conference on Embedded Networked Sensor Systems Bharadia and lead author Nagarjun Bhatt show that not only is passive sensing possible — or sensing without connection to a power source — it can be done inexpensively without any specialized equipment.

Converting goods into tools

Ph.D. An electrical engineering student, Bhatt’s research focuses on ways to enable passive sensing using simple, ubiquitous goods.

His favorite commodity? Radio Frequency Identification tags, also known as RFID tags. Essentially, these small, flexible tags receive and transmit data from a chip to an RFID reader, which processes the information and sends it to a computer program for interpretation. They are typically included in products such as clothing or library books to track inventory or in contactless fare payment cards.

Although they seem very technical – and therefore expensive – RFID tags work in between A few cents to a few dollars per slice Depending on specifications. And with up to 90% of retailers use RFID technologyChips are widespread and easy to access.

To Bhatt and Paradia, who is also a faculty member at the UC San Diego Center for Wireless Communications, these chips seemed like prime candidates for further experiments.

“We wondered if we could reuse RFID tags to do battery-free sensing and tracking,” Bhatt said. He explained that most current methods of passive sensing rely on analog-to-digital converters, which measure stimuli, record them in raw data, and convert them into digital values ​​that can be read by computers.

But these types of sensor interfaces are power-hungry; Without extra batteries, it can last for hours. Battery-based systems are bulky, expensive, and difficult to scale sustainably.

“We were trying to see if we could use the chips to sense stimuli directly without the need for transducers,” he added. “We wanted to know if it was possible to automate our environment in a way that was battery-free, capable of sensing parameters such as temperature and humidity, and could connect to the Internet of Things to send raw data to a reader that everyone could understand.”

Real-time data through RFID tags

Bhatt and Paradia were not the first to try to create passive wireless interfaces. Other researchers have pursued ultra-low-power digital sensing that combines a sensor, transducer, and microprocessor in a single package. Although these types of devices have an efficient design, they are expensive, bulky, and lack the ability to sense and report stimuli in real time. They send data to the reader only when requested and require complex electronic circuits for their interface.

One of Bhatt and Bharadi’s sensors feeds data into a computer.

“If I wanted to use digital sensing for a biomedical application like monitoring a patient’s heart rate, I might not have access to that data for 10 minutes,” Bhatt said. “This is a problem.”

Analog sensing – the category into which Bhatt and Bharadi’s sensors fall – directly perceives environmental stimuli. Unlike digital interfaces, analog interfaces convert the change in voltage/current generated by sensors into parameters of the wireless signal.

Bhatt noted that although “there is good work done so far” with passive analog systems, most research has relied on purpose-built custom sensors only suitable for a specific application. These systems are difficult to generalize, he explained, adding, “You would have to redesign all the sensors on the market to make them commercially available.”

That’s why he chose RFID tags as the backbone of his passive sensors: they’re commercial, cheap, and require little dedicated hardware to deploy or read them.

“We took the concept of analog sensing and made it real-time,” Bhatt said. “You don’t need any fancy interfaces, readers, or specialized batteries to access the data — all you need are some commercially available RFID tags, antennas, and readers.”

The future of data collection

Bhat’s battery-free RFID sensors enable new use cases such as improved agricultural management, real-time sports performance metrics and occupancy detection.

Currently, automatic irrigation systems generally rely on a smaller amount of larger sensors that cover large areas. This can be cost-effective, although it comes at the cost of data privacy. Passive RFID-based tracking devices can do both. By deploying soil moisture sensors widely around a field, it is possible to use a few RFID readers to remotely measure moisture content at a more detailed level and adjust how water is distributed based on current conditions.

This type of real-time data can also be valuable to athletes. For example, many UC San Diego athletes participate in plate strength testing as part of their training, where they jump on force plates that measure their strength, power and posture. These tests must be performed in a special facility and can be expensive. Bhatt’s paper describes how RFID sensor tags can be used to perform these tests “internally” by embedding them in the soles of shoes to measure an athlete’s jumping force.

Or RFID tags can be placed in parking lots to measure occupancy and map the location and number of spaces in use. A slide can be added to the floor of each space; When a vehicle enters the spot and covers the light-sensitive sensor, the tag recognizes that the spot is occupied and can send that information to a central location.

Ultimately, however, Bharadia and Bhat see greater uses for their work.

“AI is everywhere now,” Bharadia said, adding that AI is powered by data backed by sensors. “We are on the cusp of a revolution where new sensors will collect data that will power the next generation of artificial intelligence. Using batteryless sensors allows us to collect a lot of information that is otherwise difficult to access. It can enable data collection, and this represents “Innovation is a really important trend for the future.”

Bhatt and Paradia presented their research on November 5 at the 22nd ACM Conference on Networked Embedded Sensor Systems (SenSys 2024) in Hangzhou, China.