Effect of Unit Cell Shape on Switchable Infrared Metamaterial VO2 Absorbers/Emitters

Metamaterial absorber/emitter is an important aspect of infrared radiation manipulation. In this paper, we proposed four simple switchable infrared metamaterial absorbers/emitters with Ag/VO2 disks on the Ag plane employing triangle, square, hexagon, and circle unit cells. The spectral absorption peaks whose intensities are above 0.99 occur at ~4 μm after structure optimization when VO2 is in insulating state and disappear when VO2 becomes metallic state. The simulated electromagnetic field reveals that the spectral absorption peaks are attributed to the excitation of magnetic polariton within the insulating VO2 spacer layer, whose values exceed 1.59 orders of magnitude higher than the incident magnetic field. Longer resonant wavelength would be excited in square arrays because its configuration is a better carrier of charges at the same spans. For absorption stability, the absorbers/emitters with square and circular structures do not have any change with the polarization angles changing from 0° to 90°, due to the high rotational symmetric structure. And four absorbers/emitters reveal similar shifts and attenuations under different incident angles. We believed that the switchable absorber/emitter demonstrates promising applications in the sensing technology and adaptive infrared system.

Tungsten Nanowire Metamaterials as Selective Solar Thermal Absorbers by Excitation of Magnetic Polaritons

The present study focuses on nanowire based metamaterials with excitation of magnetic polariton (MP) as selective solar absorbers. Finite-difference time-domain simulation is employed for numerically designing a broadband solar absorber made of lossy tungsten nanowires which exhibit spectral selectivity due to the excitation of MP. An inductor-capacitor circuit model of the nanowire array is developed in order to predict the resonance wavelengths of the MP harmonic modes. The effects of geometric parameters such as nanowire diameter, height, and array period are investigated and understood on tuning the magnetic polariton resonance and the resulting optical and radiative properties. In addition, the independence of incidence angles is demonstrated, which illustrates the potential applicability of the nanowire-based metamaterial as a high-efficiency wide-angle selective solar absorber. The results will facilitate the design of novel low-cost and high-efficiency materials for enhancing solar thermal energy harvesting and conversion.