Ultra-broadband, polarization-robust terahertz metamaterial absorber based on concentric quarter-circle resonators

We propose a multilayer terahertz metamaterial absorber whose unit cell comprises concentric quarter-circle resonators stacked on a PTFE/Cu/Si substrate. Full-wave simulations show > 90% absorptance from 0.62 to 4.98 THz, yielding a ~ 156% relative bandwidth, while maintaining a stable response over a wide range of incidence angles for both TE and TM polarizations. The absorption mechanism is clarified by retrieving the effective impedance, permittivity, and permeability from simulated S-parameters, confirming near-free-space impedance matching across the high-absorptance band. Field maps (electric, magnetic, and surface currents) reveal multi-resonant coupling among the concentric arcs and the ground-backed stack that jointly broaden the bandwidth. An equivalent RLC circuit is derived from geometry-aware approximations and reproduces the main resonances in agreement with CST/ADS results. Compared with recent THz absorbers, the proposed architecture combines exceptional bandwidth, thin profile, and fabrication-friendly geometry, making it promising for detectors, filters, and sensing in the THz domain.