ABSTRACTA microwave‐based sensor for detection of cracks is proposed. Two types of resonators are designed and analyzed. The first resonator is a ring resonator with stubs attached to the rings. It resonates at a frequency of 2.3 GHz with an insertion loss of −38.51 dB and a return loss of −3.25 dB. The second resonator consists of a transmission line with a coupling in between as the waveguide. A complementary split ring resonator (CSRR) is used instead of conventional ground plane. It resonates at 4.1 GHz with an insertion loss of −26.92 dB and a return loss of −0.85 dB which is in good agreement. The two resonators were tested for cracks on surface of substrate. In the presence of cracks on the substrate, the resonators show a shift in its characteristics indicating misalignment of surfaces. A crack of 1 mm is detected for resonator using CSRR. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2745–2750, 2015