Metal Crack Sensor Based on Ring Resonator Coupled Slow Wave Structure

Irreversible cumulative damage and fatigue cracks may happen during service of metallic structure. To tackle the contradiction between the coverage and sensitivity of the conventional electromagnetic resonant sensor, a metal crack sensor with ring resonator coupled slow wave structure is studied in this paper. The resonant unit is compact due to the slow wave effect and therefore has a good detection sensitivity. The coupled resonator realizes a slow wave transmission, resulting in a long-scale coverage. The sensor uses the average amplitude of the transmission coefficient S21 in the passband as a feature. The sensor can distinguish longitudinal cracks at a depth of 0.5 mm and is less sensitive to crack position. The average sensitivity of crack depth detection is 0.042/mm.