Passive Chipless RFID Sensors: Concept to Applications—A Review

In this paper, a review of frequency-coded (FC) passive chipless RFID sensors is presented. The prime aim of this review paper is to discuss the key concept of a passive chipless RFID sensor and its classification according to fundamental sensing parameters. The fundamental sensing parameter refers to the intrinsic characteristics of a sensor that is sensitive to an environmental parameter to be sensed. The widely used intrinsic parameters are effective permittivity, effective electrical length, and electromagnetic coupling. The categorization of frequency-coded passive chipless RFID sensors based on fundamental sensing parameters facilitates the future researcher to better understand the operating principle of the diverse RFID sensors. The improved understanding helps in the advanced design and implementation of RFID sensors. In addition, the key performance measures and recent areas of applications are discussed. This paper also focuses on existing challenges and the scope of the further developments of frequency-coded passive chipless RFID sensors.