Quarter-Mode Spoof Localized Surface Plasmons for Differential Microwave Sensing

In this letter, a differential microwave sensor designed based on quarter-mode spoof localized surface plasmons (SLSPs) is presented. The differential sensor consists of two independent sensors each exciting a symmetrically structured resonance unit, and the size of the differential sensor is reduced by a factor of one by the composition of two independent quarter modes. A prototype of this sensor has been fabricated, and measurements have been performed on dielectric substrates with different dielectric constants and on ethanol solutions with different concentrations. The experimental results show that the sensor has an average relative sensitivity of 1.64% and 0.18% when measuring solids and liquids respectively. This work is applicable to the detection of dielectric constant of solid materials and liquid concentration in industry.