Bandwidth improvement in copper-based terahertz metamaterial absorbers by structural engineering

Terahertz (THz) absorbers, whether narrowband or broadband, are essential for developing advanced THz detectors, imagers, and sensors. We demonstrate two terahertz metamaterial absorbers based on conventional metal/dielectric/metal three-layer architectures to meet narrowband and broadband application demands. The narrowband absorber combines a periodic circular copper resonator array with a gold reflector through a TOPAS dielectric spacer, achieving 99.8% absorption at 8.344 THz. This design exhibits dual-band operation with varying incident angles, polarization insensitivity, tunability, and exceptional refractive index sensing performance (1.626 THz/RIU sensitivity across n = 1.0-1.4), making it ideal for biosensing. A broadband meta-absorber is also developed, extending the design by integrating copper-based patches, including solid circles, ring-shaped circles, and split-ring resonators with varied radii and spatial arrangements. The resulting broadband absorber achieves high absorption exceeding a bandwidth of 1.218 THz (TE polarization), outperforming existing copper-based meta-absorbers. This strategy establishes a framework for tailoring absorption bandwidths in terahertz systems through resonator geometry optimization.