Chiral Metamaterial for Sensing Dielectric Objects Based on Cross-polarization Conversion Ratio at Microwave Frequencies

This work demonstrates the detection of external dielectric objects interacting with the chiral metamaterial (CMM) based on cross-polarization. A bi-layered CMM is realized, which converts the x-polarized wave into a y-polarized wave with a polarization conversion ratio (PCR) above 80% in the frequency range of 5.918 GHz to 6.072 GHz. The highest PCR of 97.8% is recorded at a frequency of 6.027 GHz for the proposed CMM. When dielectric cylindrical items were randomly placed on top of the CMM, a significant change in PCR was detected. The change in PCR indicates that the designed CMM can be utilized for detecting dielectric objects in two distinct manners: (i) An increase in relative permittivity of external dielectric objects results in a redshift of the cross-polarization resonance (CPR). (ii) The change in PCR is linear for linear rise in the dielectric constant of the external dielectric objects. We have examined dielectric sensing concerning random arrangements, the density and dimensions, morphology, and quantity of particles. Expanding the proposed concept of sensing through polarization detection using CMM in the terahertz/optical domain may improve the sensing for detecting microplastics and monitoring the environment.