Complementary Split-Ring Resonator (CSRR)-Loaded Sensor Array to Detect Multiple Cracks: Shapes, Sizes, and Positions on Metallic Surface

Single-resonance-based radio frequency (RF) resonators cannot detect multiple cracks simultaneously nor localize the position of a crack. To address these drawbacks, we propose a complementary split-ring resonator (CSRR)-loaded array. In this array, there are four channels and each channel consists of three CSRRs, forming a 4 x 3 sensing array that is developed in the ground plane of a microstrip line using a low-cost FR4 substrate. A voltage-controlled oscillator (VCO) generates three discrete frequencies: 1.88 GHz, 2.60 GHz, and 3.61 GHz to each channel, which is sequentially selected using a singlepole four-throw (SP4T) switch. The transmitted RF signals are converted into the DC voltage levels and are interpreted by a microcontroller. Aluminum sheets with cracks embedded in the surface are used to demonstrate the detection of cracks of various shapes, sizes and locations/orientations (horizontal, diagonal, and vertical) with simulations and measurements. The detection of the minimum detectable crack (W-c x L-c x D-c = 1 mm x 10 mm x 0.1 mm) is experimentally verified. Full-length longer cracks (Lc D 100 mm) are also detected using our proposed detection system with the SP4T switch in addition to our proposed algorithm that scans the CSRRs of each selected channel.