High performance solar-selective absorbers using coated sub-wavelength gratings

Dept. of Electrical Engineering, Stanford University, Stanford, CA 94305 USA.
Optics Express (Impact Factor: 3.49). 03/2010; 18(6):5525-40. DOI: 10.1364/OE.18.005525
Source: PubMed


Spectral control of the emissivity of surfaces is essential for efficient conversion of solar radiation into heat. We investigated surfaces consisting of sub-wavelength V-groove gratings coated with aperiodic metal-dielectric stacks. The spectral behavior of the coated gratings was modeled using rigorous coupled-wave analysis (RCWA). The proposed absorber coatings combine impedance matching using tapered metallic features with the excellent spectral selectivity of aperiodic metal-dielectric stacks. The aspect ratio of the V-groove can be tailored in order to obtain the desired spectral selectivity over a wide angular range. Coated V-groove gratings with optimal aspect ratio are predicted to have thermal emissivity below 6% at 720K while absorbing >94% of the incident light. These sub-wavelength gratings would have the potential to significantly increase the efficiency of concentrated solar thermal systems.

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Available from: Peter Peumans, May 06, 2014
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    • "When a time-varying magnetic field is introduced to the structure, oscillating antiparallel currents are induced that creates magnetic resonances, i.e., magnetic polaritons (MPs). MPs have been used to control radiative properties of thermal emitters and absorbers [7- 14], which have wide practical application areas such as wavelength-selective thermal emitters and absorbers, thermophotovoltaics [15] [16] [17] [18] [19] [20] [21], and biosensors [22]. These emitters and absorbers can be applied not only near to the infrared region, but also gigahertz to terahertz regions [23]. "
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    ABSTRACT: Electromagnetic metamaterial emitters and absorbers rely on a variety of electromagnetic resonances (i.e., polaritons) with different metallic nano/microstructured patterns such as strips, squares, circular disks, crosses, and square rings. A unique mechanism exists for different structures with various metallic patterns due to the similarity of the configuration. Thus, we explore a unified model which can greatly simplify the design process of these nano/microstructures. In the present study, an inductor-capacitor (LC) circuit model is used to predict the magnetic resonance conditions or magnetic polaritons (MPs) for metamaterial emitters and absorbers with different shapes. By suitably adjusting some of the parameters, the LC circuit model can reasonably predict the resonance conditions for published experimental results as well as rigorous electromagnetic wave simulations for the fundamental MP mode regardless of the shape of the metallic patterns. This study may facilitate the initial design of metamaterial emitters and absorbers.
    Full-text · Conference Paper · Aug 2014
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    • "Micro/nanostructures of wide profile diversity are able to tailor thermal radiation by utilizing different physical mechanisms. Not only one-dimensional (1D) gratings [12] [13], V-groove gratings [14], and photonic crystals [15] [16] [17], but also various two-dimensional (2D) nano/microstructures have been investigated as promising selective TPV emitters. Heinzel et al. [18] manufactured 2D wavelength-selective emitters for the near-infrared spectral range, but the emittance exhibited directional dependence. "
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    ABSTRACT: Thermophotovoltaic (TPV) devices can convert thermal radiation directly into electricity. To improve the efficiency of TPV systems, wavelength-selective emitters are designed to take thermal energy from various heat sources and then emit photons to the TPV cells. A two-dimensional grating/thin-film nano-structure is proposed as an efficient emitter, whose performance is enhanced by the excitations of both surface plasmon polaritons (SPPs) and magnetic polaritons (MPs). Rigorous coupled-wave analysis is used to predict the emittance as well as the electromagnetic field and current density distributions. The normal emittance of the proposed nanostructure is shown to be wavelength-selective and polariza-tion-insensitive. The mechanisms of SPP and MP excitations in the nanostructure are elucidated for different polarizations. The current–density loop further confirms the existence of magnetic resonances. Furthermore, the effect of azimuthal and polar angles on the emittance spectra is also investigated, suggesting that the proposed structure has high emittance not only in the normal direction but also at large oblique angles.
    Full-text · Article · Aug 2013 · International Journal of Heat and Mass Transfer
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    • ", [2], [5], [12], [14], [15], [32]. As shown in Fig. 1, the geometry of the grating structure is characterized by the period , the grating ridge width and the grating thickness . "
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    ABSTRACT: The wavelength-selective infrared absorptance of a single-layered aluminum subwavelength structure (SWS) is optimized using a hybrid numerical scheme comprising the rigorous coupled-wave analysis method and a genetic algorithm. The results show that the optimized SWS yields a strong absorptance peak (0.99) and a full-width-at-half-maximum (FWHM) of 1.42 μm. In addition, it is shown that the absorptance spectrum of the SWS is insensitive to the angle of incidence of the incoming light and the grating period, but shifts toward a longer (shorter) wavelength as the grating thickness or grating ridge width is increased (decreased). The enhanced absorptance is examined by computing the governing equations of the excitations of Rayleigh-Wood anomaly, surface plasmon polaritons, cavity resonance, and magnetic polaritons. The magnetic field patterns and Poynting vector distribution within the grating structure are also analyzed to support the physical mechanism using the finite-difference time-domain (FDTD) method. The results indicate that the absorptance peak of the SWS is the result of cavity resonance. Also, for a double-layered SWS comprising an aluminum grating and a dielectric layer, a widening of the absorptance spectrum occurs. Overall, the results presented in this study show that SWS gratings which can be easily manufactured using microfabrication technology provide a simple and versatile solution for such applications in tailoring the spectral absorptance used for infrared detection, energy harvesting, and so on.
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