Purpose RFID tags for sensing are available to operate and transmit sensing data to measurement equipment without battery and wires, which is a great advantage in establishing IoT environment. For crack sensing tags, however, the short service life of tags restricted their application. This paper aims to introduce a method of surface crack detection and monitoring based on RFID tag, which makes it possible for tags to be reused. Design/methodology/approach Metal plate to be monitored, acting as the ground plane of microstrip patch antenna, is underneath the crack sensing tag. The propagating surface crack in metal plate will change the electric length of tag’s antenna that is directly proportional to the crack depth and length. Thus, the deformation of sensing tag introduced by the load on metal structure is no longer a prerequisite for crack sensing. Findings The simulated and experimental results show that the proposed crack sensing tag can sense the change of surface crack with mm-resolution and sense surface crack propagation without a deformation, which means the proposed crack sensing tag can be reused. Originality/value The key advantage of the proposed method is the reusability of the RFID tags.

Purpose Crack sensor based on RFID tag has become a research hotspot in the field of metal structural health monitoring for its significant benefit of passive wireless transmission. While in practice, crack location will impact the performance of crack depth-sensing tag. The purpose of this paper is to provide a method for reducing disturbance of crack location on crack depth-sensing tag. Design/methodology/approach The effect analysis of crack location on crack depth-sensing tag is presented first to find disturbance reason and disturbance law. On the basis of that, a miniaturized tag is proposed to improve the current distribution and reduce the disturbance introduced by crack location. Findings The degree of crack location disturbance is closely related to the current distribution in the coverage area of tag. Because sensing tag performs better when crack locates in the high current density area, miniaturization of sensing tag is exploited to expand the high current density area and make the area more symmetrical. The simulated and experimental results demonstrate that tag miniaturization can enhance the performance of crack depth-sensing tag. Originality/value This paper provides a method to enhance the performance of crack depth-sensing tag.

Purpose Radio frequency identification tags for passive sensing have attracted wide attention in the area of Internet of Things (IoT). Among them, some tags can sense the property change of objects without an integrated sensor, which is a new trend of passive sensing based on tag. The purpose of this paper is to review recent research on passive self-sensing tags (PSSTs). Design/methodology/approach The PSSTs reported in the past decade are classified in terms of sensing mode, composition and the ways of power supply. This paper presents operation principles of PSSTs and analyzes the characteristics of them. Moreover, the paper focuses on summarizing the latest sensing parameters of PSSTs and their matching equipment. Finally, some potential applications and challenges faced by this emerging technique are discussed. Findings PSST is suitable for long-term and large-scale monitoring compared to conventional sensors because it gets rid of the limitation of battery and has relatively low cost. Also, the static information of objects stored in different PSSTs can be identified by a single reader without touch. Originality/value This paper provides a detailed and timely review of the rapidly growing research in PSST.