Metasurface Design for Sensing Applications

Abstract

Measurements of material properties are essential in all fields of Science specially agriculture, RF and civil engineering. More precisely, the measurement of dielectric constant of materials is one of the challenging tasks. To find out dielectric constant of materials, different sensing techniques are used. All of these sensors work on the principle of spectral shift in their resonance frequencies corresponding to the change in the relative permittivity. These techniques involve disadvantages such as large spectral dispersions with resonant shapes, high absorption losses and complex measurement setups. This thesis presents a novel sensing technique based on the shift in the polarization state of the test sample through a metasurface to measure the unknown dielectric constant of the sample. The polarization state sensing involves the detection of the co- and cross- currents induced on the metasurface at single frequency. Their magnitudes are proportional to the magnitude and phase of the reflected field components, thereby eliminating the need of frequency sweep. This unique sensing through polarization state offers an additional degree of freedom over conventional methods and therefore allows monochromatic sensing capability with high accuracy. The proof of concept for polarization state sensing is demonstrated experimentally at microwave frequencies and the dielectric characteristics of the samples embedded inside the metasensor are extracted from calibrated polarization state data. This opens up new opportunities for realizing low cost sensing device, while maintaining high sensitivity of overall sensor system. This thesis also includes an anisotropic dual broadband polarization converter metasurface. The surface can efficiently transform linearly polarized electromagnetic (EM) wave into its orthogonal components in X and Ku bands.