A Microwave Flexible Antenna-Sensor based on SRR for Contactless Characterization of Permittivity

In this article, a microwave flexible antenna-sensor based on Split Ring Resonator (SRR) is proposed for the contactless characterizing of permittivity. The High-Frequency Structure Simulator (HFSS) is used for modeling and optimization, resulting in sensor parameters with a high Q-factor. Meanwhile, HFSS is employed to simulate the processes of both traditional testing methods and wireless testing methods, highlighting the high sensitivity and strong compatibility with measured objects of the designed sensor. To achieve sensor flexibility, a 0.1mm polyimide (PI) film is used as the sensor substrate, and the screen-printing process is adopted to fabricate the SRR electrodes. A test platform is built to measure the permittivity performance of the sensor and the transmission performance between the interrogation antenna and the sensor. The measurement results are roughly consistent with the simulation results, exhibiting high sensitivity for permittivity measurement. Specifically, the sensitivity is 4.13% when the permittivity of the measured object ranges from 1 to 6, and 2% when the range is 6 to 10. Owing to its advantages such as flexibility, small size, high sensitivity, and strong compatibility, the designed sensor has broad application.