Octagonal Nested CSRR Sensor for Improved Liquid Permittivity Sensing

Abstract In this work, an octagonal shaped CSRR has been modified to form a nested structure for achieving a better field-material interaction. This modification results in an increase in the electrical length of the resonator providing higher sensitivity while accurately determining the complex permittivity of unknown samples. The resonator has been designed using High Frequency Structure Simulator (HFSS) software with its structural dimensions chosen to operate at 2.4 GHz of the ISM band. It has been fabricated on a low-cost FR4 substrate where the nested CSRR structure is etched on the ground plane. A lumped equivalent circuit model of the proposed design is further developed using Advanced Design System (ADS) software for the validation of the operating principle of the sensor. Some commonly available liquids covering a wider range of dielectric constants have been used to develop an equation between the permittivity parameters of the liquid and the transmission coefficients of the resonator. The sensor has effectively predicted both the real and imaginary parts of permittivity of toluene and aniline used as unknown samples with accuracy as high as 97%. The average and normalized sensitivity of the proposed sensor have been found to be 78.34 MHz/ε' and 3.273% respectively. A comparison of this work with other recently reported works clearly indicates the superiority of this work and its potential to be used as a dielectric sensor.