Chipless RFID sensor for metal crack monitoring

This paper presents a chipless Radio Frequency Identification (RFID) sensor for detecting the angle and width of metal cracks in engineering structures. Its resonators are composed of square and rectangular patches. By exciting the sensor with linearly polarized waves in the frequency range of 3.8-6.9 GHz, four resonance frequencies are generated in X and Y polarization, respectively. The angle and width of cracks can be identified by analyzing the direction and magnitude of frequencies shifts. Its sensitivity can reach up to 50.0 MHz/0.1 mm with sub-millimetre resolution. This sensor has a simple structure and high reliability. It supports real-time monitoring and can utilize polarization multiplexing technology to save frequency band resources.