Tags: Innovation, Sensors

Posted on 11 Jun,2019

A team of researchers from the University of Michigan and the University of Washington have completed the first round of testing for an RFID-based system that uses UHF RFID signals to identify a specific tag, and that uses fluctuations in these signals to understand changes in the field around that tag. The result could be a solution with which users could understand whether a tagged item has been moved or been interacted with, as well as if someone has approached or left the tag’s vicinity.

The project, known as IDAct, has been underway throughout the 2018 to 2019 school year as researchers have worked to design a way to gain more information from a simple RFID tags read than just its ID number. The IDAct system takes advantage of received signal strength (RSSI), as well as RFID’s built in “phase” functionality, according to Alanson Sample, an associate professor at the University of Michigan and a co-author of the project’s white paper, titled “IDAct: Towards Unobtrusive Recognition of User Presence and Daily Activities.” The question Sample posed was how to turn basic UHF tags into little sensors. “The idea I had,” he says, “was to use a communication channel as a sensing mechanism.”

RFID readers built into light fixtures read tagged items to track a person’s daily activities in a test apartment.

The system leverages changes in the RSSI and phase, as reported by the RFID reader, as well as machine learning, to infer what is happening around a tag. Traditionally, RFID readers and the software that manages the collected read data focus on receiving a unique ID number from a passive RFID tags, but they can also use RSSI to determine approximately where that tag is located, or the direction in which it is moving.

IDActs take that a step further by using the RF phase measurement. UHF RFID readers randomly change their transmission frequency across 50 channels, from 902 to 928 MHz, in order to meet FCC regulations and minimize interference with other devices. These changes in frequency take place at 0.2-second intervals. The phase difference between channels can be dramatically increased with motion, or due to a person’s presence.


The phase-sensing capability of RFID is what makes the IDAct system possible, Sample explains. One unique aspect of UHF RFID systems, he says, is that users can measure the phase of backscattered signals, which can be used to identify such details as a tag’s exact location; other technologies, such as Wi-Fi or Bluetooth Low Energy (BLE), lack a phaseresponse.

The system has been tested in a dedicated apartment with 10 test volunteers, to detect such information as when a person entered or left a room and when he or she interacted with the tagged objects. The tags were attached to such items as toothbrushes, food packaging and pill bottles.

The team now plans to look for industry partners that could help to build out the technology for use in elder-care settings. Sample (from the University of Michigan) and Hanchuan Li (of the University of Washington) co-developed the technology with Shwetak Patel (also at the University of Washington) and Intel’s Chieh-yih Wan and Raul Shal.