This work presents a non-invasive, reusable and submersible permittivity sensor that uses a microwave technique for the dielectric characterization of liquid materials. The proposed device consists of a compact split ring resonator excited by two integrated monopole antennas. The sensing principle is based on the notch introduced by the resonators in the transmission coefficient, which is affected due to the introduction of the sensor in a new liquid material. Then, a frequency shift of the notch and the Q-factor of the proposed sensor are related with the changes in the surrounding medium. By means of a particular experimental procedure, commercial liquids are employed to obtain the calibration curve. Thus, a mathematical equation is obtained to extract the dielectric permittivity of liquid materials with unknown dielectric properties. A good match between simulated and experimental results is obtained, as well as a high Q-factor, compact size, good sensitivity and high repeatability for use in sensing applications. Sensors like the one here presented could lead to promising solutions for characterizing materials, particularly in determining material properties and quality in the food industry, bio-sensing and other applications.

This work presents the performance analysis of a compact electrical permittivity sensor based on monopoles-coupled Split Ring Resonator to measure the dielectric properties changes in liquids. The sensor was designed and fabricated on standard FR4 substrate with a dielectric constant ε _r =4.4 with 1.56 mm of thickness and the optimized dimension of 35 × 50 mm ² . Simulation results are made using finite element method. The sensor sensitivity is obtained based on the shift of its resonance frequency when the permittivity of the material surrounding the resonator is altered. A remarkable shift of resonance frequency is observed upon introduction of several samples with different permittivity values in a range of 16 to 30, with a sensitivity of -81.9 MHz/Δε. Finally, some experimental measurements with samples of acetone and ethanol were performed to validate the operation of the proposed sensor.