Liquid Pressure Sensing System With Coupling RFID and HMM Based on Distance Measurement

Liquid pressure measuring is of increasingly importance to promote sustainable operation of civil and industrial equipment. In this paper, a novel approach based on distancemeasurement is proposedby usingRadio Frequency Identification (RFID) and Hidden Markov Model (HMM). Two RFID tags, which interrogated by reader, are mainly used to build a liquid pressure sensing system (LPSS). At the same time, an ultra-high-frequencyRFID chip with self-tuning capability aiming to achieve impedancematching is exploited. While HMM takes pride in its real-time processing and high efficiency so as to make a reasonable prediction of liquid pressure. The feasibility of proposed scheme is verified by double tags coupling circuit design and simulation. Through hardware construction and testing, reliable pressure measurement is achieved in an indoor scenario (0.5cm <= d <= 7cm). Meanwhile, parameter evaluating model (PEM) and sequential estimation model (SEM), which are based on Maximum Likelihood Estimation (MLE) and HMM respectively, have been proposed to achieve online denoising.