Noncontact Group-Delay-Based Sensor for Metal Deformation and Crack Detection

A millimeter-wave planar resonator sensor for the detection of deformation and crack in metal device with high precision and sensitivity is presented in this article. The deformation and crack directly imply great damage in the industrial metal structures, which made the detection crucial in structural health monitoring. The main structure of the proposed sensor is based on the concept of multiband electromagnetic induced transparency (EIT) effect. EIT effect is an interference quantum phenomenon, which can be realized in microwave band by electromagnetic resonate structures. Multiband EIT is actualized using a series of split-ring resonators (SRR) coupling with each other to produce one wide stopband and four narrow passbands. The resonance frequencies of the SRRs are affected by the variation of coupling amount between the SRRs and the part of metal device under test that places close to the specific SRR. The orientation of metal deformation and crack is achieved by different frequency shifts of the four independent group delay peaks induced by multiband EIT. Thus, the proposed sensor can orientate the deformation on the metal device with the precision of 1.3 MHz/μm.