RFID to Track Body Movements for Novel Smart Technologies

Researchers at Carnegie Mellon University have developed ways to use RFID tags to track movement, allowing integration of the tags into next-generation wearable designs and other smart applications.

RFID tags have been around long enough that they are almost an overlooked technology in terms of new advancements. However, Carnegie Mellon University (CMU) researchers have found a new way to use the technology to track body movements and detect shape changes, leading to two RFID-based innovations that can lead to novel wearable designs, researchers said in a CMU news release.


RF-Wear technology developed at Carnegie Mellon University calculates skeletal motion by analyzing radio signals reflected by RFID tags positioned on either side of each joint. (Image source: Carnegie Mellon University)

Proven Design

It’s the proven, well-used aspect of the tags’ design—cheap, battery-free, and washable—that make them attractive for these new applications, said Haojian Jin, a Ph.D. student in CMU's Human-Computer Interaction Institute (HCII). Jin was part of a team that designed two technologies—called RF-Wear and WiSH—using RFID tags to track body movements in unique ways. "We're really changing the way people are thinking about RF sensing," he said.

The team devised a new method for tracking the tags, which results in the monitoring of movements and shapes using a single, mobile antenna to monitor a tag array without the prior calibration that is usually needed, he said. RFID technology typically uses multiple antennas to track signal backscatter and triangulate the locations of the tags, but for this application, it wouldn’t make sense, researchers said.

Works Two Ways

The technology developed by the CMU team works in two ways—either based on whether the tags are used to track the body's skeletal positions or to track changes in shape, Jin explained.

For body-movement tracking, researchers positioned an array of RFID tags on either side of the knee, elbow, or other joints. They can calculate the angle of bend in a joint by keeping track of the very slight differences in when the backscattered radio signals from each tag reach the antenna, he said. "By attaching these paper-like RFID tags to clothing, we were able to demonstrate millimeter accuracy in skeletal tracking," Jin said.

The clothing they developed with this technology is called RF-Wear, and researchers envision it could be an alternative to systems such as Kinect, which use a camera to track body movements. The drawback to Kinect, however, is that it only works when the person is in the camera's line of sight.

Wearable Technology

RF-Wear also could be an alternative to existing wearable technology that depends on expensive, power-consuming sensors that are difficult to maintain, Jin said. It also can be applied to RFID-embedded clothing that can be used as a fitness tracker similar to wrist-worn devices like FitBits, he said. "Weaving these tags into clothing will only add a minimal cost—under $1," Jin said.

The technology for monitoring changes in curves or shapes that the team developed is called WiSh—short for Wireless Shape-aware world. It also uses arrays of RFIDs and a single antenna, as well as relying on a sophisticated algorithm for interpreting the backscattered signals to infer the shape of a surface, researchers said.

"We can turn any soft surface in the environment into a touch screen," said Jingxian Wang, Jin’s co-researcher and a Ph.D. student at CMU. Indeed, the technology could be integrated into various smart fabrics to track a user's posture, or even into objects—like smart carpets or toys—that can detect and/or respond to user movements, he said.

Researchers published a video demonstrating the technology on YouTube.

Another use for WiSh could be in place of sensors to monitor the structural health of bridges or other infrastructure, Wang said. Researchers also demonstrated this by measuring the curvature of Pittsburgh's 10th Street Bridge using a robot to drag a string of 50 RFID tags along the bridge's sidewalk.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.


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