Non-resonant dual-channel microwave sensor for enhanced crack detection

Cracking under fatigue stress is a common defect in metallic structures during operation. Owing to random sizes and locations of cracks, monitoring techniques require large-scale deployment involving complex sensor design and layout. Electromagnetic resonance sensors offer simple structure and high sensitivity, but their coverage is limited and performance significantly influenced by crack position. Achieving sensitivity and precision over large area remains a critical challenge for electromagnetic sensors. This paper proposes a dual-channel (four-port) array sensor with interwoven resonant rings between microstrip lines to enable energy exchange and expand detection range simultaneously. The sensor operates in a non-resonant band to generate smoother field distribution, while averaged transmission coefficient magnitudes between ports serves as a crack feature to enhance performance. For 1.0-mm-wide cracks, it achieves normalized sensitivity of 0.141/mm2 and precision of 25.05% of full scale (F.S.). The proposed sensor is suitable for health monitoring of large-scale metallic components.