Polarization-insensitive quasi-bound states in the continuum supported by terahertz all-metallic complementary periodic cross-shaped resonators

Abstract A strategy to design polarization-insensitive quasi-bound states in the continuum (BICs) metasurfaces based on symmetry-broken metamolecules is introduced. Such metasurfaces consist of four complementary periodic cross-shaped resonators (CPCRs), forming a novel C4 structure through rotating arrangements, whose resonant qualities can be improved by optimizing the slit length. Unlike single CPCRs sensitive to polarization changes, experimental results demonstrate that the constructed metasurface exhibits the same spectral response when the polarization angle alters, despite a 2.4 GHz frequency variation found in these simulated resonances. This polarization-insensitive quasi-BIC show a frequency shift of 67.1 GHz when a 20 μ m-thick polyimide membrane is attached. Modification of the structural parameters also has an impact on its sensing performance. The study provides a way to achieve high-quality resonances with polarization-insensitive properties that can be easily applied to high-sensitivity sensor design for THz sensing.