Browsing by Author "Didari, Azadeh"
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ArticlePublication Metadata only Analysis of near-field radiation transfer within nano-gaps using FDTD method(Elsevier, 2014-10) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehEnhancement 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.ArticlePublication Open Access A biomimicry design for nanoscale radiative cooling applications inspired by Morpho didius butterfly(Nature Publishing Group, 2018-11-15) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehIn 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.Conference paperPublication Open Access Biomimicry designs for passive optical solutions for nanoscale radiative cooling applications(SPIE, 2018) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; Lakhtakia, A.; Mackay, T. G.; MENGÜÇ, Mustafa Pınar; Didari, AzadehInspired 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.ArticlePublication Metadata only A design tool for direct and non-stochastic calculations of near-field radiative transfer in complex structures: The NF-RT-FDTD algorithm(Elsevier, 2017) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehAdvances 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).Conference paperPublication Metadata only Localized near-field radiative heat transfer in biomimicry designs inspired by neon tetra fish(Begell House Inc., 2019-06) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehInspired by multilayer structure of the Neon tetra tropical fish which is one of the most fascinating multilayer systems ever reported in nature, we investigate the localized effects of coupling of surface phonon polaritons in phononic multilayer geometries. Our findings suggest that near-field radiative heat flux can be enhanced by orders of magnitude when compared against the blackbody predictions in the proposed structures. These biomimicry structures which give rise to structural colours and their iridescent characteristics, may find potential in design, modelling and manufacturing of spectrally selective thermal and electronic sensors when used in the proposed platform as presented in this work.Conference paperPublication Metadata only Near to far-field thermal emission by nanoparticles on a substrate: Evaluation of effective medium theory(The Optical Society, 2014) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehWe study the near to far-field thermal emission of a thin SiC film with/without nanospheres placed upon it. We show that Effective Medium Theorem produces questionable results when approximating emission and absorption effects of nanoparticles.PhD DissertationPublication Metadata only Near- and far-field thermal radiation in metamaterials and the development of NF-RT-FDTD algorithm(2016-06) Didari, Azadeh; Mengüç, Mustafa Pınar; Yaralıoğlu, Göksenin; Ertürk, H.; Erkol, Güray; Şendur, K.; Department of Electrical and Electronics Engineering; Didari, AzadehIn 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.ArticlePublication Metadata only Near- to far-field coherent thermal emission by surfaces coated by nanoparticles and the evaluation of effective medium theory(The Optical Society, 2015) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehNear-field thermal radiation may play significant role in the enhancement of energy harvesting and radiative cooling by new types of designer materials, which in turn can be crucial in the development of future devices. In this work, we present a case study to explore near- to far-field thermal emission and radiative flux from a thin polar SiC film coated by different size and shape nanoparticles. The same geometry with nano-particles is also considered as a layered medium, which is analyzed using Effective Medium Theory (EMT). A significant enhancement of emission, particularly at the far infrared, is observed when nanoparticles are placed on the surface of a SiC film with certain periodicities, which shows potential use of these structures for radiative cooling applications. Yet, these enhancements are not observed when the EMT approach is adapted, which is questioned for its accuracy of predicting near-to-far field transition regime of radiation transfer from corrugated surfaces.ArticlePublication Metadata only Near-field thermal emission between corrugated surfaces separated by nano-gaps(Elsevier, 2015) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehNear-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.ArticlePublication Open Access Near-field thermal radiation transfer by mesoporous metamaterials(The Optical Society, 2015-09-21) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehIn 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.CorrectionPublication Open Access Publisher correction: A biomimicry design for nanoscale radiative cooling applications inspired by Morpho didius butterfly(2019-02-26) Didari, Azadeh; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehA correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper. The original PDF version of this Article contained a truncated Figure 4. This error has now been corrected in the PDF version of the Article; the HTML version was correct from the time of publication.ArticlePublication Metadata only Tunable near-field radiative transfer by III–V group compound semiconductors(IOP Publishing, 2019-03-06) Elçioğlu, E. B.; Didari, Azadeh; Özyurt, T. O.; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Didari, AzadehNear-field radiative transfer (NFRT) refers to the energy transfer mechanism which takes place between media separated by distances comparable to or much smaller than the dominant wavelength of emission. NFRT is due to the contribution of evanescent waves and coherent nature of the energy transfer within nano-gaps, and can exceed Planck's blackbody limit. As researchers further investigate this phenomenon and start fabrication of custom-made platforms, advances in utilization of NFRT in energy harvesting applications move forward day by day. In designing and manufacturing such harvesting devices, chemical and physical properties of surfaces and wafers are important for development of effective solutions. In this work, we compare several III-V group compound semiconductor wafers (mainly GaAs, InSb, and InP) from fabrication point of view, in order to explore their possible use in future devices. The results presented here show that the type of dopant, wafer temperature, and gap size are very important factors as they affect the NFRT rates. GaAs, InSb, and InP wafers significantly enhance the near-field fluxes beyond the blackbody rates, and n-type InSb yields to the highest enhancement. For GaAs, p-type yielded a higher radiative flux compared to n-type GaAs, as oppose to n-type InSb outperforming its p-type and undoped counterparts. Furthermore, the possible use of n-InSb as the TPV cell at 550K is discussed for effective energy harvesting. These findings can be useful for determination of the proper material type for emitting and non-emitting NFRT-based energy harvesting devices.