Biomimicry designs for passive optical solutions for nanoscale radiative cooling applications

Inspired by the mechanism of the wings of Morpho butterfly, here we propose biomimicry designs which have the potential to be used for radiative cooling purposes. We numerically analyzed the spontaneous emission at near-field and determined radiative heat flux at nano-scale in order to investigate the impact of geometric variations and material selection in these systems. Our findings suggest that these metasurfaces which support phononic surface waves, can be used to tailor radiative heat transfer at nano-scale in the atmospheric transparency window (8-13 mu m) within the infrared regime

Adaptive Plasmonic Metasurfaces for Radiative Cooling and Passive Thermoregulation

In this work, we investigate a class of planar photonic structures operating as passive thermoregulators. The radiative cooling process is adjusted through the incorporation of a phase change material (Vanadium Dioxide, VO2) in conjunction with a layer of transparent conductive oxide (Aluminum-doped Zinc Oxide, AZO). VO2 is known to undergo a phase transition from the “dielectric” phase to the “plasmonic” or “metallic” phase at a critical temperature close to 68°C. In addition, AZO shows plasmonic properties at the long-wave infrared spectrum, which, combined with VO2, provides a rich platform to achieve low reflections across the atmospheric transparency window, as demanded in radiative cooling applications, while also maintaining a compact size. Using numerical analysis, we study two classes of patterned and non-patterned compact multilayer metal-dielectric-metal metasurfaces, aiming to maximize the overall absorption in the first atmospheric transparency window (8–13 µm) while maintaining a high reflection across the solar spectrum (0.3–2.5 µm). Surfaces are initially designed based on a round of coarse optimization and further improved through analyzing the impact of geometric parameters such as size and periodicity of the metasurface elements. Our findings are relevant to applications in thermal regulation systems and passive radiative cooling of high-temperature devices, such as electronic elements

Near-field thermal radiation transfer by mesoporous metamaterials

In this work, we investigate the impact of nano-scale pores within structured metamaterials on spectral near-field radiative transfer. We use Finite Difference Time Domain Method (FDTD) and consider uniform and corrugated SiC substrates filled with rectangular nano-scale vacuum inclusions having equivalent diameters of 10, 37 and 57 nm. We report the appearance of the secondary and tertiary resonance peaks at different frequencies as a function of changing pore diameter, which cannot be predicted if an effective medium theory approximation is used.TÜBİTAK ; European Commission ; CEE

Near- and far-field thermal radiation in metamaterials and the development of NF-RT-FDTD algorithm

Thesis (M.A.)--Özyeğin University, Graduate School of Sciences and Engineering, Department of Electrical and Electronics Engineering, June 2016.In this dissertation, analysis of near-field regime of thermal radiative transfer in metamaterials supporting surface phonon polaritons (SPhPs) is given. Solutions of electromagnetic fields at subwavelength distances are studied where combined effects of surface waves and total internal reflection, result in enhancement of thermal radiation by orders of magnitude when compared against far-field regime of thermal radiation which is obtainable through Planck's blackbody law. We have developed Near Field Radiative Transfer Finite Difference Time Domain (NF-RT-FDTD) algorithm which is developed based on Finite Difference Time Domain (FDTD) method specifically designed to provide full solutions to near-field radiative transfer problems by solving Maxwell's equations combined with fluctuation-dissipation theory. We have extensively investigated the near- and far-field thermal emission and heat flux profiles in different geometries with corrugations and porosities of various size and shapes and report on our findings which reveals a high degree of accuracy is attainable by NF-RT-FDTD method in complex geometries. We have compared our results against solutions of effective medium theory which makes effective medium theory's ability to provide accurate solutions highly questionable. NF-RT-FDTD could be used to provide solutions for complex geometries with different applications, including energy harvesting with near-field thermophotovoltaics, radiative cooling, thermal sensing, nano manufacturing and medical diagnostics.Bu doktora tezinde, yüzey fonon polaritonlarını (SPhP) destekleyen metamalzemeler içerisinde yakın alanda gerçekleşen ışınım ısı transferi incelenmiştir. Işınım ısı transferinde Plank'ın siyah cisim ışınımı ile tanımlanan uzak alan ışınımına kıyasla, yüzey dalgaları (surface waves) ve toplam iç yansımanın (total internal reflection) etkileşim etkileri nedeniyle mertebeler ölçüsünde artış gösteren ışınım dalga boyundan daha küçük mesafelerdeki elektromanyetik alanların çözümlemesi kullanılmıştır. Yakın alan ışınımının çözümlenmesinde; özellikle Maxwell denklemlerinin dalgalanmalı dağılım teorisi (fluctuation dissipation theory) ile birlikte çözümü sonucu elektromanyetik ve ısıl çözümleri elde etmeyi mümkün kılacak şekilde tasarlanmış sayısal bir yöntem olan Zaman Ortamında Sonlu Farklar Yöntemi (FDTD) temelli sayısal bir yöntem olarak NF-RT-FDTD (Near Field Radiative Transfer Finite Difference Time Domain) algoritması geliştirilmiştir..Çeşitli boyut ve şekillerde oluklar ve gözenekler içeren farklı geometriler için yakın ve uzak alan emisyonu ve ısı akısı profilleri kapsamlı olarak incelenmiş ve bu karmaşık geometrilerin çözümlenmesinde NF-RT-FDTD yönteminin kullanımı ile yüksek doğrulukla sonuç elde edilebildiği saptanmıştır. NF-RT-FDTD yöntemi ile elde edilen sonuçlar, etkin ortam kuramının (effective medium theory) çözümleri ile karşılaştırılmış ve etkin ortam kuramı ile elde edilen sonuçların tartışmaya açık olduğu belirlenmiştir. Sonuç olarak, NF-RT-FDTD yöntemi, yakın alanda termofotovoltaik uygulamalar, ışınımla soğutma, ısıl algılama, nano ölçekte üretim ve tıbbi tanılama gibi uygulamalarda kullanılabilecek karmaşık geometriler için sonuçlar elde etmede kullanılabileceği gösterilmiştir

A design tool for direct and non-stochastic calculations of near-field radiative transfer in complex structures: The NF-RT-FDTD algorithm

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Advances in nanotechnology and nanophotonics are inextricably linked with the need for reliable computational algorithms to be adapted as design tools for the development of new concepts in energy harvesting, radiative cooling, nanolithography and nano-scale manufacturing, among others. In this paper, we provide an outline for such a computational tool, named NF-RT-FDTD, to determine the near-field radiative transfer between structured surfaces using Finite Difference Time Domain method. NF-RT-FDTD is a direct and non-stochastic algorithm, which accounts for the statistical nature of the thermal radiation and is easily applicable to any arbitrary geometry at thermal equilibrium. We present a review of the fundamental relations for far- and near-field radiative transfer between different geometries with nano-scale surface and volumetric features and gaps, and then we discuss the details of the NF-RT-FDTD formulation, its application to sample geometries and outline its future expansion to more complex geometries. In addition, we briefly discuss some of the recent numerical works for direct and indirect calculations of near-field thermal radiation transfer, including Scattering Matrix method, Finite Difference Time Domain method (FDTD), Wiener Chaos Expansion, Fluctuating Surface Current (FSC), Fluctuating Volume Current (FVC) and Thermal Discrete Dipole Approximations (TDDA).TÜBİTAK ; the European Commissio

Analysis of near-field radiation transfer within nano-gaps using FDTD method

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Enhancement of near-field radiative emission via coupling of surface plasmons in nano-gaps formed between thin films is important for understanding and implementation of energy harvesting using nano-thermophotovoltaic cells. Design and construction of such cells need to be carried out along with detailed modeling studies, necessitating accurate calculation of near-field emission within thin films. The objective of this paper is to provide a methodology based on finite difference time domain analysis for the calculation of the near-field thermal radiation emission based on local density of electromagnetic states. Near-field thermal emission is investigated within the nano-gap formed between thin silicon carbide layers where both support surface phonon polaritons. Modeling of this problem with the FDTD method is not trivial particularly for establishing the Drude–Lorentz permittivity model and the selection of the right boundary conditions. We present an effective boundary condition, for calculation of Local Density Of electromagnetic States (LDOS) via Finite Difference Time Domain Method (FDTD) for applications to nano-scale geometries. We conclude that Convolutional Perfectly Matched Layer (CPML) is the optimum boundary condition that gives the most accurate results compared against the other methodologies for parallel plates separated by nano-gaps. This boundary condition allows more streamlined simulations to be carried out when working with sub-wavelength structures. The challenges and the possible solutions to overcome these difficulties are discussed in detail.TÜBİTAK ; European Commission ; CEE

Near-field thermal emission between corrugated surfaces separated by nano-gaps

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Near-field thermal radiation with its many potential applications in different fields requires a thorough understanding for the development of new devices. In this paper, we report that near-field thermal emission between two parallel SiC thin films separated by a nano-gap, supporting surface phonon polaritons, as modeled via Finite DifferenceTime Domain Method (FDTD), can be enhanced when structured nanoparticles of different shapes and sizes are present on the surface of the emitting films. We compare different nano-particle shapes and discuss the configurations, which have the highest impact on the enhancement of near-field thermal emission and on the near-field heat flux. Convolutional Perfectly Matched Layer (CPML) boundary condition is used as the boundary condition of choice as it was determined to give the most accurate results compared against the other methodologies when working with sub-wavelength structures.TÜBİTAK ; European Commission ; CEE

A biomimicry design for nanoscale radiative cooling applications inspired by Morpho didius butterfly

Abstract In nature, novel colors and patterns have evolved in various species for survival, recognizability or mating purposes. Investigations of the morphology of various butterfly wings have shown that in addition to the pigmentation, micro and nanostructures within the wings have also allowed better communication systems and the pheromone-producing organs which are the main regulators of the temperature within butterfly wings. Within the blue spectrum (450–495 nm), Morpho didius butterfly exhibit iridescence in their structure-based wings’ color. Inspired by the rich physics behind this concept, we present a designer metamaterial system that has the potential to be used for near-field radiative cooling applications. This biomimicry design involves SiC palm tree-like structures placed in close proximity of a thin film in a vacuum environment separated by nanoscale gaps. The near-field energy exchange is enhanced significantly by decreasing the dimensions of the tree and rotating the free-standing structure by 90 degrees clockwise and bringing it to the close proximity of a second thin film. This exchange is calculated by using newly developed near-field radiative transfer finite difference time domain (NF-RT-FDTD) algorithm. Several orders of enhancement of near-field heat flux within the infrared atmospheric window (8–13 μm bandwidth) are achieved. This spectrally selective enhancement is associated with the geometric variations, the spatial location of the source of excitation and the material characteristics, and can be tuned to tailor strong radiative cooling mechanisms

A design tool for direct and non-stochastic calculations of near-field radiative transfer in complex structures: The NF-RT-FDTD algorithm

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Advances in nanotechnology and nanophotonics are inextricably linked with the need for reliable computational algorithms to be adapted as design tools for the development of new concepts in energy harvesting, radiative cooling, nanolithography and nano-scale manufacturing, among others. In this paper, we provide an outline for such a computational tool, named NF-RT-FDTD, to determine the near-field radiative transfer between structured surfaces using Finite Difference Time Domain method. NF-RT-FDTD is a direct and non-stochastic algorithm, which accounts for the statistical nature of the thermal radiation and is easily applicable to any arbitrary geometry at thermal equilibrium. We present a review of the fundamental relations for far- and near-field radiative transfer between different geometries with nano-scale surface and volumetric features and gaps, and then we discuss the details of the NF-RT-FDTD formulation, its application to sample geometries and outline its future expansion to more complex geometries. In addition, we briefly discuss some of the recent numerical works for direct and indirect calculations of near-field thermal radiation transfer, including Scattering Matrix method, Finite Difference Time Domain method (FDTD), Wiener Chaos Expansion, Fluctuating Surface Current (FSC), Fluctuating Volume Current (FVC) and Thermal Discrete Dipole Approximations (TDDA).TÜBİTAK ; the European Commissio