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Near-perfect spectrally-selective metasurface solar absorber based on tungsten octagonal prism array.

ABSTRACT: Solar selective absorbers influence the photothermal efficiency of high-temperature solar thermal applications directly and significantly. In present work, a metasurface absorber consisting of an octagonal prism array is proposed, optimized and analyzed. Firstly, the structure parameters of the absorber are optimized, finding the optimal absorber achieves near-perfect spectrally-selectivity compared with the perfect solar absorber. The high solar absorptivity of 0.9591, low emissivity of 0.1594-0.3694, and high photothermal efficiency of 94.72-83.10% are achieved at 1073-1573 K and 1000 suns. Then, the mechanisms leading to the excellent spectral selectivity are investigated, suggesting that the coupling effects of multi-plasmon resonance modes and the impedance matching lead to the high solar absorptivity. Meanwhile, the impedance mismatching is the mechanism to minimize the emissivity in the mid-IR region. Moreover, whether the spectral absorptivity can be changed by structural parameters is investigated, suggesting that the excircle diameter of the first tungsten octagonal prism and the height of SiO₂ under the octagonal prism can influence the spectral absorptivity obviously. Finally, the metasurface absorber is demonstrated to be highly insensitive to both polarization and incident angles. These results suggest that the proposed metasurface absorber should be suitable for high-temperature solar thermal devices.

SUBMITTER: Xu M

PROVIDER: S-EPMC9172566 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The geometry of the characteristic element forming the artificial structure of an electromagnetic metamaterial defines the way the metamaterial will interact with electromagnetic waves, and accordingly, how it will transmit, reflect, and absorb electromagnetic energy. Metamaterials have been discovered that can manipulate electromagnetic waves to create perfect absorption of incident electromagnetic energy using relatively simple elemental geometries. But the phenomenon is confined to very narrow frequency bandwidths owing to the mono-resonance characteristics of simple cellular structures. Complex cellular geometries based on the combination of many different fundamental building blocks may be able to constructively couple many more resonances and broaden the perfect absorption bandwidth. We describe here a metasurface based upon geometric inversion of a set of conformal mapping contours. The resulting geometry forms a nearly continuous series of perfect absorption resonances within an ultrathin (λ/165) metasurface to develop broadband absorption in a frequency range of interest for downhole chemical spectroscopy. The metasurface is derived from a geometric inversion of the Rhodonea, or more commonly called four-leaf roses, conformal mapping contours and was found to exhibit a near zero index metamaterial (NZIM) behavior. An uncooled microbolometer design is described that uses the metasurface geometry on a single VO2 thermometric substrate leading to an infrared detector with predicted maximum absorption of 99.94% at 4.3 μm and an absorption bandwidth of 170% FWHM on 15.8 μm center wavelength, coincident with important chemical spectra of downhole hydrocarbons. The infrared detector design has a predicted maximum detectivity D* = 1.5 × 109 cm[Formula: see text]/W and noise equivalent difference temperature NEDT of 70 mK at a frame rate of 60 Hz. These levels of detector performance conventionally would be achievable only with cryogenically cooled technologies and could represent a significant step in the effort towards deploying an in situ infrared chemical spectroscopy sensor into downhole logging applications.

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Near-perfect spectrally-selective metasurface solar absorber based on tungsten octagonal prism array.

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