Microwave Planar Sensor Based On a Single Octagonal Split Ring Resonator for Permittivity Sensing

In this article, a microwave planar sensor based on a single octagonal split-ring resonator is presented, which can work in the millimeter-wave band. The usefulness of the millimeter-wave band can offer high sensitivity to liquids and low conductivity to impurities in the material under test (MUT). The microwave planar sensor is composed of a single octagonal-shaped connected by two strip lines on the top of the substrate and a full ground plane at the back. It has a length of 22 mm and a width of 10 mm. The purposed of the microwave planar sensor is to detect the change of the dielectric constant value of the liquid solution. The numerical results demonstrate that when a MUT with a higher permittivity value is placed in the gap, the S21 response shifts to a lower frequency band. Hence, the presented microwave planar sensor based on a single octagon-shaped split-ring resonator can provide a feasible approach with excellent sensitivity and can detect the permittivity of several liquid solutions in the millimeter-wave band.