A comprehensive review of passive RFID sensors for structural health monitoring: Developments, challenges, and opportunities

In this paper, a detailed review of passive RFID sensors for structural health monitoring applications, i.e., crack quantification, strain deformation, and corrosion detection for metallic materials, is presented. The state-of-the-art developments in passive RFID sensors are elaborated, i.e., chip-based RFID sensors, retransmission-based chipless RFID sensors, and backscattering-based chipless RFID sensors. Advanced methodologies for feature extraction, selection, and fusion techniques are thoroughly analyzed. Based on the literature, this paper highlights the technical issues, including joint communication and sensing (JCAS), miniaturization of sensor dimensions, orientation insensitivity to tag, quality factor optimization, conductivity improvement, reliability, and system robustness. In the end, these studies suggest the future direction of the research in terms of novel designing of phase-array antenna and metamaterial-assisted chipless RFID sensors, aiming to overcome the current limitations and pave the way for highly sensitive, robust sensors.