Polarization-insensitive five-band metamaterial absorber based terahertz sensor using graphene convoluted resonator

Abstract This paper deals with the design of a polarization-insensitive absorber for terahertz (THz) applications. The absorber comprises a graphene-based convoluted resonator on a polyimide substrate with a copper ground plane, forming a metal–dielectric–graphene stack that facilitates multi-resonant behaviour. Simulations show five distinct absorption bands at 0.85, 1.45, 2.37, 2.89 and 5.00 THz, each exhibiting absorptivity greater than 96%. Owing to its symmetric configuration, the absorber properties remain independent of polarization and offers angular stability up to 60° under both Transverse Electric (TE) and Transverse Magnetic (TM) incidences. The analysis of electric field distributions indicates that the lower-order resonances originate from dipolar and loop current modes, while the higher-order responses are governed by plasmonic confinement in graphene and coupling between the convoluted arms. This hybrid resonance mechanism accounts for the stable five-band absorption. In comparison with conventional single- or dual-band designs, the proposed Perfect Metamaterial Absorber (PMA) offers a compact footprint, improved angular stability and reliable multi-band operation, making it well-suited for THz sensing and filtering applications. As a material sensor, the PMA achieves sensitivities of 313, 346, 313, 374, and 511 GHz per Refractive Index Unit (RIU) across its five operating frequency bands. Furthermore, the sensitivity variation with respect to analyte thickness is less than 4 GHz/μm, ensuring stable and reliable sensor performance. These results show the potential of the proposed PMA for high-precision terahertz material and bio-sensing applications.