Reconfigurable Wireless Passive Sensor for Highly Sensitive Crack Detection

Cracks in metal structures are common defects that require monitoring over large areas, often necessitating numerous sensors. This wiring and layout increase design and deployment complexity. Traditional electromagnetic resonant sensors, while simple and sensitive, are limited in coverage. In response, this paper proposes a wireless passive sensor based on electrically reconfigurable resonant rings. These rings, integrated directly onto a microstrip line, confine electromagnetic fields within miniaturized resonant units, significantly enhancing sensitivity. Through electrically control the working sequence of the resonant rings, the sensor can eliminate the impact of inter-unit mutual coupling, enabling the detection of crack depth and width in sub-millimeter level. The proposed sensor has been configured to two states: status 1 (resonant frequency is 955 MHz) and status 2 (resonant frequency is 903 MHz). The measured sensitivities for crack width characterization are 163.9 MHz/mm² and 153.5 MHz/mm², respectively and the measured sensitivities for crack depth characterization are 125.75 MHz/mm² and 128.5 MHz/mm², respectively. This paper demonstrates its suitability for large-scale coverage in metal components.