Ultra-thin metasurface absorbers for spectro-polarimetric radiation detectors: In-depth electromagnetic analysis and practical design for subterahertz band

摘要

We present the results of extensive theoretical and experimental investigations of high-performance ultra-thin metasurface-based radiation absorbers designed for narrow-band operation at subterahertz (subTHz) frequencies and intended for integration with spectro-polarimetric sensors of a thermal type. Implemented in a three-layered configuration with a capacitive frequency selective surface (FSS) backed by a grounded dielectric slab, the absorbers are analyzed in terms of minimizing their thickness-to-wavelength (d / λ) ratio and absorption bandwidth, while maximizing the FSS unit cells subwavelengthness and free dispersion range for absorption spectra. A choice of optimal material parameters and a role of near-field “FSS - ground plane” coupling are discussed and an optimal FSS pattern for a “spectrometric” absorber is deduced. Supplemented with experimental measurements in the range of 0.1-1 THz demonstrating feasibility of attaining d / λ~1/200 at the bandwidth of several percent, original cost-effective metasurface-absorber-based schemes for uncooled thermal subTHz sensing with spectrometric, polarimetric, and imaging capabilities are also considered.