Carmina burana vocal score pdf. The Portable Document Format (PDF) is a popular format to publish formatted text and documents. There are several different versions of it, some qualifying as. Control of thermal radiation at high temperatures is vital for waste heat recovery and for high-efficiency thermophotovoltaic (TPV) conversion. Previously, structural resonances utilizing gratings, thin film resonances, metasurfaces and photonic crystals were used to spectrally control thermal emission, often requiring lithographic structuring of the surface and causing significant angle dependence. In contrast, here, we demonstrate a refractory W-HfO 2 metamaterial, which controls thermal emission through an engineered dielectric response function. The epsilon-near-zero frequency of a metamaterial and the connected optical topological transition (OTT) are adjusted to selectively enhance and suppress the thermal emission in the near-infrared spectrum, crucial for improved TPV efficiency. The near-omnidirectional and spectrally selective emitter is obtained as the emission changes due to material properties and not due to resonances or interference effects, marking a paradigm shift in thermal engineering approaches. We experimentally demonstrate the OTT in a thermally stable metamaterial at high temperatures of 1,000 °C. The photonic isofrequency surface relates the momentum and energy of optical modes inside a medium and can be engineered using metamaterials. As opposed to regular spherical and ellipsoidal shapes seen in natural dielectrics, we can engineer exotic isofrequency surfaces in metamaterials. Examples include point-like vanishing surfaces as in epsilon-near-zero (ENZ) media and open surfaces as in hyperbolic media. These surfaces support unique electromagnetic modes that can be used in sub-diffraction imaging and waveguiding, spontaneous emission engineering and nanoscale resonators. An important experimental problem is the thermal excitation of metamaterial modes lying on this unique photonic isofrequency surface for practical thermal applications. Our aim in this paper is to demonstrate a high-temperature metamaterial with wavelength selective thermal emission arising from the ENZ behaviour associated with the optical topological transition (OTT) in the photonic isofrequency surface. This marks an important departure from well-established routes of two-dimensional and three-dimensional photonic crystals,,,,,,,,,, thin film resonances,,,, gratings and metasurfaces,,,,,, since we control an intrinsic material property and bulk thermal energy density to selectively excite and suppress bulk metamaterial modes that contribute to far-field thermal emission. Furthermore, we do not utilize resonances or bandgap effects and achieve the effect by tuning the ENZ frequency (plasma frequency) of a metamaterial. We show that the experimentally observed far-field thermal radiation spectrum is a unique signature of the change in the reflectivity of the metamaterial that occurs due to the topological transition in the isofrequency surface. The metamaterial is designed based on a subwavelength super-lattice structure with refractory materials tungsten and hafnium oxide in stark contrast to previous ENZ and hyperbolic media which have utilized noble metals with low-temperature stability, phonon-polaritonic materials, graphene, and highly doped semiconductors. ![]() ![]() We conclusively demonstrate the high-temperature stability of the optical absorption and thermal emission at temperatures of 1,000 °C. The OTT is carefully designed to lie in the near-infrared window (1–3 μm wavelength) paving the way for refractory metamaterials compatible with low-bandgap photovoltaic (PV) cells,,, (0.3–0.6 eV). We strongly emphasize that the unique selective thermal emission spectrum at the OTT is desirable for high-efficiency thermophotovoltaic (TPV) system proposals. In exchange for improved conversion efficiency and application flexibility the implementation of the TPV concept places stringent requirements on the emissivity characteristics and thermal stability of the selective thermal emitter,. Thermodynamic conservation arguments require the radiative thermal emissivity of any object to be less than that of a blackbody at the same temperature. Consequently, to achieve sufficient output radiative power density in the range of contemporary low-bandgap photovoltaic receivers with bandgaps of typically 0.55 eV operational temperatures surpassing 1,000 °C are required. The emitter should also possess the highly selective emissivity characteristics required to suppress the emission of long-wavelength photons and, at the same time, should provide near unity emissivity at energies above the bandgap of the PV cell,.
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