Tailoring thermal radiative properties with film-coupled concave grating metamaterials

•Selective absorption was numerically realized with film-coupled concave gratings.•Underlying mechanisms were elucidated as magnetic and surface plasmon polaritons.•An inductor-capacitor model was employed to confirm the magnetic polaritons.•Dispersion relation was used to explain the behavior of surface plasmon polariton.•Effects of geometric factors, oblique angle and polarization were also discussed.

This work numerically investigates the radiative properties of film-coupled metamaterials made of a two-dimensional metallic concave grating on a continuous metal film separated by an ultrathin dielectric spacer. Spectrally-selective absorption is demonstrated in the visible and near-infrared regime, and underlying mechanisms are elucidated to be either localized magnetic polaritons (MPs) or surface plasmon polaritons (SPPs). The unique behaviors of MPs and SPPs are explained with the help of electromagnetic field distributions at respective resonance frequencies. An inductor-capacitor model is utilized to further confirm the excitation of MP, while dispersion relation is used to understand the behaviors of different SPP modes. Geometric effects of ridge width and grating period on the resonance absorption peaks are discussed. Moreover, directional responses at oblique incidences for different polarization states are studied. Fundamental understanding gained here will facilitate the design of novel metamaterials in energy harvesting and sensing applications.