DropMonitor: Millimeter-level Sensing for RFID-based Infusion Drip Rate Monitoring

As an important indicator of the infusion monitoring for clinical treatment, the drip rate is expected to be monitored in an accurate and real-time manner. However, state-of-the-art drip rate monitoring schemes either suffer from high maintenance or incur high hardware cost. In this paper, we propose DropMonitor, an RFID-based approach to perform the mm-level sensing for infusion drip rate monitoring. By attaching a pair of batteryless RFID tags on the drip chamber, we can estimate the drip rate by capturing the RF-signals reflected from the vibrating liquid surface caused by the falling droplets. Particularly, we use the sensing tag to perceive the liquid surface vibration in the drip chamber and further derive the drip rate for infusion monitoring. Moreover, to sufficiently mitigate the multi-path interference from the surrounding human activities, we use the reference tag to perceive the multi-path signals from the indoor environment. By computing the difference of RF-signals from tag pairs, we cancel the multi-path interference and extract the drip-rate-related signals. We have implemented a prototype system and evaluated its performance in real applications. The experiment results show that DropMonitor can accurately estimate the infusion drip rate, and the average relative error of drip rate estimation is below 1% for conventional cases. In this way, considering the essential sampling rates of each tag, DropMonitor is able to monitor the drip rate for over a dozen of infusion bottles/bags in parallel with one COTS RFID system.