In-situ surface crack detection on metal using a passive wireless RFID-based NDT sensor

In-situ structural health monitoring is essential for the early detection of surface cracks at dedicated stress locations. This paper presents a circular-shaped RFID sensor design for wireless surface crack detection on metal. The sensor was designed in the HFSS software tool with a diameter of 50 mm in dimension. Simulation analysis was performed for varying crack depths and widths at sub-millimeter resolution. The sensor is sensitive enough to detect a minimum crack depth of 0.2 mm. The average resonant frequency gradient $(\Delta)$ is used to differentiate the varying crack depths and widths. For varying crack depths, the observed $\Delta$ values are 2.1 MHz and 6.1 MHz for sub-mm and mm resolution, whereas for varying crack widths, the values are 2 MHz and 7.6 MHz, respectively. Simulated crack samples are fabricated and examined using conventional Eddy USB to illustrate the pros and cons of passive wireless surface crack detection using an RFID-based NDT sensor.