Ultrahigh-Sensitivity and Compact EBG-Based Microwave Sensor for Liquid Characterization

In this letter, an ultrahigh-sensitivity microwave sensor based on an electromagnetic band gap (EBG) structure is proposed. The proposed sensor consists of step via EBG and suspended microstrip line. Two low-cost polypropylene pipes are used to place the liquid under test (LUT) above the EBG patch, which changes the effective dielectric constant of the substrate, and therefore, frequency shift and change in the peak of attenuation of transmission response are observed. The change in the resonance frequency and peak attenuation is used to measure the complex permittivity of the LUT. A matrix-based model is developed to retrieve the complex permittivity of the LUT. A prototype of the proposed sensor is fabricated and tested with a good agreement between the calculated and reference values. The average relative sensitivity of 0.588 is achieved for the proposed sensor with a size of 0.198
$\lambda _{o}$
× 0.198
$\lambda _{o}$
.