Cornell University have created a new touch-free monitoring system that can monitor a patient’s blood pressure, heart rate, and breathing with a small RFID tag. The researcher says, the device is small, robust and can withstand washing, thus, it could be sewn into a hospital gown or a bed sheet. In such an arrangement, each patient would be monitored by one or more of the devices without attaching anything to the body. The benefits of this device are making patients more comfortable and make it faster, easier, and cheaper to monitor the patients for hospitals and care facilities.
The system needs a RFID tag and small antenna to be placed near the chest and a wrist. They can far away the body from a distance of 10 centimeters and an RFID reader is placed two meters away. The antenna not only uses near-field coupling to direct part of the electromagnetic energy from the RFID reader into body tissue, but also reflects part of it back to the receiver. Then, the receiver reads both the phase and amplitude of the reflected signal. The external motions like pulse and breathing make tag move and change phase, because that the phase is sensitive to the distance between the antenna and the receiver. As the same time, heartbeats change the amplitude of what the antenna reflects back to the detector. And the system also measures blood pressure by measuring the slight time pause between pulse and heartbeat.
Kan and his graduate student Xiaonan Hui have been working on a solution that monitoring several tags at same time by near-field coupling. The researchers incorporated a code-division multiple access (CDMA) module in the RFID tag chip. CDMA is the wireless communication protocol that allows several signals to be mixed and transmitted over the same channel. In this case, reader can detect dozens of tags by a unique code signal from RFID tag. The engineers’ simulations show that a single system can monitor the vital signs of dozens of people in a room by monitoring about 200 tags.
Kan says, the previous RFID-based vital sign-monitoring systems have a low signal-to-noise ratio, thus they fail to achieve that monitoring several tags at same time. However, the near-field antenna coupling creates a clean enough signal.