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Michigan Researchers Develop RFID-based Sensors to Measure Physical Activity

The system would enable physicians or therapists to capture sophisticated data about an individual's expended energy, based on the movement, angle and relative position of three EPC Gen 2 RFID tags worn on that person's body.
By Claire Swedberg
Sep 21, 2010When doctors want to monitor a patient's activity level, either for sports-medicine or weight-management applications, they generally have to rely on that individual's own account of his or her activity, or on a small pedometer worn by the patient when going about his or her daily routine. Researchers at Michigan State University (MSU), however, have developed a system that takes a leap ahead of the former methods, by using a network of RFID-enabled sensors to track not only the movements of different body parts, but also their angle and proximity to each other.

The system includes three RFID tags: one attached to a person's upper arm, another on a wrist and a third on one of the ankles. Each tag communicates with the other two, enabling the system's software to calculate the amount of movement and angle of a person's limbs, as well as determine how close they are to each other.

MSU graduate student Dong Bo wears the prototype sensor tags developed by Subir Biswas and his team. Photo by G.L. Kohuth.
The system was the result of collaboration between MSU's electrical engineering and kinesiology departments, according to Subir Biswas, an electrical engineering professor who serves as the department's associate chair for research and is also the director of the university's Networked Embedded and Wireless Systems (NeEWS) Laboratory. Its development is being funded by the National Institute of Health (NIH). Biswas has a background in low-power wireless networking, and after he began working in June 2008 with Karin Pfeiffer, an assistant professor of kinesiology at MSU, he discovered a way in which the technology could be employed in the medical or physical training arena.

Accelerometers traditionally provide a way to measure the quantity of activity in which an individual is engaged, by counting footsteps and other major movements. The number of those movements recorded by the accelerometer can then be entered directly into a computer by hand—or, in some cases, the data on the device can be uploaded to a computer. But the accelerometers alone provide very little visibility into smaller body movements, or the position the body is in throughout the day, which are details that could impact an individual's health. "In reality," Biswas says, "the amount of metabolic energy being expended is difficult to gauge with an accelerometer alone."

What Biswas and his team of researchers developed was a wearable RFID tag with three different sensors: one that measures tilt, to determine the angle of the body part wearing that sensor; an accelerometer, to monitor the number of body movements; and a proximity sensor, to ascertain how close the tag is to the other two on the body (which requires the sensors to transmit to each other). A total of three tags are attached to a subject's body—typically, to a person's wrist, upper arm and ankle. In this way, users can gain much more sophisticated data regarding a body's movement and positioning throughout the day.

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