Reliability and performance of embedded RFID-MEMS sensors for monitoring humidity in cementitious materials exposed to corrosive environments

RFID-MEMS sensors offer significant potential for non-destructive structural health monitoring, yet their reliability and performance when embedded in concrete and exposed to corrosive environments remain poorly understood. This study addresses this gap by systematically investigating the degradation mechanisms of RFID-MEMS sensors under realistic exposure conditions. Sensors were placed in 3D-printed enclosures acting as a smart spacer and embedded in concrete for seven months, followed by two months of direct exposure to 3% wt. NaCl solution and 100% relative humidity (RH), and one year of fatigue testing by weekly exposure to wetting and drying cycles. Degradation indicators — including changes in RH, surface corrosion and morphological changes were analysed to assess reliability. Results indicate that sensor performance remained stable in concrete when protected by 3D-printed enclosures. However, a 10% deviation in RH measurements occurred following 63 days of NaCl exposure. Surface degradation was observed on the silicon thin films, capacitors, and resistor solder joints under these conditions, manifested through increased surface voidage and elevated carbon content. Notably, after one year of fatigue testing, sensor performance remained highly consistent, with a maximum deviation of 1% compared to unexposed controls. This work provides critical insights into MEMS sensors durability and establishes a validated methodology for non-destructive monitoring of reinforced concrete structures.