Real-Time Measurement of Liquid Permittivity Through Label-Free Meandered Microwave Sensor

In this paper, a microwave sensor with a meandered microstrip structure is introduced to measure the permittivity of the various liquids. The performance of the sensor is based on the change of operating resonance frequency during the absence and presence of materials in the sensing area. In this study, liquids including ethanol, methanol, aqueous glucose solution, and deionized water have been selected as samples under test. The proposed sensor has been implemented on RO4003 substrate with dimensions of 35 × 20 × 0.508 mm3 and operating frequency of 6.21 GHz in a free load state with a Q-factor of 506. When the samples are present in the sensing area, the frequency of the sensor shifts from 5.42 to 3.27 GHz. The sensitivity of 0.64% is obtained for the presented sensor. Compact size, linearity of changes, and low cost are the most important advantages of the sensor. The introduced sensor can be used in various fields of industrial, medical, and diagnostic due to its performance.