Non-destructive Testing and Evaluation of Surface-Breaking Cracks using Microwave Planar Resonator Probe

Metallic structures are commonly employed for innumerable applications across various industries. However, stress, fatigue and corrosion can lead to manifestation of surface-breaking cracks. Non-destructive testing (NDT) of such anomalies is incumbent to maintain integrity and health of metal structures. Apart from well-known and standard NDT techniques, microwave -based inspection of cracks dates back to 1960s and has been demonstrated as a reliable modality for detection and characterization of cracks. In this paper, we present the utility of an ultra-high frequency (UHF) probe towards detection and characterization of crack on metal surface. Simulation analysis of resonance frequency shift as a function of crack width is corroborated with experimental results rendering a close match. In addition to this, the higher sensitivity of one the resonances of the probe against the other is also explained herein with the aid of field distributions and surface current maps rendered by simulations. The effect of change in magnitude with crack width is also studied. Lastly, the imaging capability of the probe towards detection of fine micro crack of width 0.07 mm is also illustrated. Overall, the potential of the probe as a reliable inspection tool for detection and characterization of micro cracks is demonstrated.