Microwave sensor based on complementary circular spiral resonator for non-destructive testing of cracks in dielectric plate

A microwave sensor inspired by the complementary circular spiral resonant structure is designed in this paper for the non-destructive testing of dielectric material plate. The sensor is designed based on the complementary circular spiral resonator (CCSR) which has two resonance frequencies in the considered frequency band. Frequency shift and variation of S₁₁ parameter is observed when the sensor is put over materials under testing (MUT). This also happens when the cracks exist in the sample. This phenomenon can be applied for the non-destructive testing of the cracks existing in the dielectric plates. Numerical results are given in the paper for a detailed discussion of the variation of the resonance frequencies and the S₁₁ parameter for different MUT and the orientations of the cracks.