Passive UHF RFID-based sensor: Influence of electrical conductivity and localized surface cracks on industrial-grade metal specimens

Early detection and localization of initial-phase surface cracks on metal structures is critical, as they can propagate and severely compromise the structural integrity of bridges, pipelines, rail, and aerospace structures. This paper presents the study of a passive wireless RFID-based crack sensor for in-situ surface crack detection on industrial-grade metal specimens of varying conductivity. A circular-shaped, symmetrical microstrip antenna-based RFID crack sensor was designed in the Ansys HFSS tool operating in the UHF region. Simulation analysis was performed for varying surface crack depths and widths in millimeter resolution for the most commonly used Aluminum Alloy 6061 and Hot-Rolled Steel 1084 grade metal specimen. It is observed that the sensor resonant frequency variation is different for varying crack depths and widths and also for varying metal specimen grades. Preliminary no-crack measurement results illustrate that the sensor RSSI and Phase change values are sensitive with respect to changes in metal specimen conductivity. It is observed that upon calibration, the sensor crack detection capability can be leveraged to diverse industrial-grade metal specimens.