A passive temperature radio-sensor for concrete maturation monitoring

A planar “T” like passive UHF RFID temperature sensor is here proposed for application inside the fresh concrete at the purpose to hydration monitoring during the curing procedure into caissons. Since the concrete's electromagnetic parameters significantly change along with the drying process, the antenna modeling and design consider both the electromagnetic and the chemical phenomena. The described tag layout is such to separate, by means of a two-conductor transmission line, the sensing device, e.g. a specialized RFID IC placed up to 15cm deep into the concrete, from the scavenging element, placed instead outside the concrete. Computer simulation and then extensive laboratory experimentation in real conditions demonstrated that, despite of the low sensitivity of the IC and the high losses of concrete, the proposed RFID sensor tag provides reasonable communication performance in passive mode with read ranges up to 2 meters, and fast and reliable temperature sensing capabilities that look comparable with that of more invasive and costly wired measurement systems.