Microwave Sensor Array Based on Differential Mode Detection Strategy

A novel microwave sensor array utilizing a differential-mode detection strategy is introduced for localized material defect detection. Two types of modified split-ring resonators (SRRs) with unloaded Q-factor above 437 and 290, respectively, are utilized to construct the basic differential sensing elements. By arranging these elements with different sizes, a sensor array can be realized. Since the distinct resonant frequency of each element, multiple transmission zeros are included in the working range. Each resonance zero corresponds to an independent region of the material under test (MUT). Any local defect will cause a split in the corresponding resonant frequency. Therefore, detection results can be obtained simply by observing the split points in the resonance spectrum, eliminating the need for further calibration. This letter presents the coupling mechanisms of the proposed two basic sensing units and the operating principle of the proposed sensor array. A prototype operating from 2.4 to 4.6 GHz with five independent differential units has been designed and fabricated. Three different samples with local defects were used for validation.