Enabling Fine-Grained Residual Liquid Height Estimation With Passive RFID Tags

For many industrial and healthcare applications, liquid volume, especially residual volume monitoring, is one of the most important problems. Yet, existing technologies mainly rely on specialized sensors, which greatly restricts their universality in other applications. The popularity of radio frequency identification (RFID) provides us with unprecedented opportunities for building wireless and batteryless sensing systems. In this article, we propose a fine-grained residual liquid height estimation scheme with passive RFID tags. With dual-tags attached to the surface of the container, our scheme takes one of them as a sensing tag and the other one as a reference tag. We establish a continuous liquid height estimation model based on the extracted differential minimum response threshold (DMRT) features of the two tags. We implement a prototype system with commercial off-the-shelf (COTS) RFID devices and conduct extensive experiments to evaluate its performance. Experimental results demonstrate that our scheme is immune to location changes and robust against interference (such as walking around people), with an overall accuracy of 95.55%.