We describe a simple and robust method using an internal reflection element acting as an infrared waveguide to measure the spectra of near-field thermal emission. We experimentally demonstrate the spectrally-narrow peaks of near-field thermal emission by isotropic media due to the excitation of surface phonon-polaritons in quartz and amorphous silica and due to the frustrated total-internalreflection modes in amorphous silica and polytetrafluoroethylene. Additionally, we demonstrate the broadband near-field thermal emission of hyperbolic modes in hexagonal boron nitride which is an anisotropic uniaxial medium. We also present a theoretical approach based on the fluctuational electrodynamics and dyadic Green's functions for one-dimensional layered media for accurate modeling of the measured spectra.
Graphene's near-field radiative heat transfer is determined from its electrical conductivity, which is commonly modeled using the local (wavevector independent) Kubo and Drude formulas. In this letter, we analyze the non-locality of the graphene electrical conductivity using the Lindhard model combined with the Mermin relaxation time approximation. We also study how the variation of the electrical conductivity with the wavevector affects near-field radiative conductance between two graphene sheets separated by a vacuum gap. It is shown that the variation of the electrical conductivity with the wavevector, π π , is appreciable for π π s greater than 100π 0 , where π 0 is the magnitude of the wavevector in the free space. The Kubo model is obtained by assuming π π β 0, and thus is not valid for π π > 100π 0 . The Kubo electrical conductivity provides an accurate estimation of the spectral radiative conductance between two graphene sheets except for around the surface-plasmon-polariton frequency of graphene and at separation gaps smaller than 20 nm where there is a non-negligible contribution from electromagnetic modes with π π > 100π 0 to the radiative conductance. The Drude formula proves to be inaccurate for modeling the electrical conductivity and radiative conductance of graphene except for at temperatures much below the Fermi temperature and frequencies much smaller than 2π π β , where π π and β are the chemical potential and reduced Planck's constant, respectively. It is also shown that the electronic scattering
Analytical expressions for calculating the energy density and spatial correlation function of thermal emission by a homogeneous, isothermal sphere of arbitrary size and material are presented. The spectral distribution and the power law governing the distance-dependent energy density are investigated in the near-field and far-field regimes for silicon carbide (dielectric), silicon (semiconducting) and tungsten (metallic) spheres of various size parameters ranging from X = 0.002 to 5. The spatial coherence of thermal field emitted by spheres of different size and material is also studied in both radial and polar directions, and the effect of localized surface phonons (LSPhs) on the correlation length and angle is elucidated. It is shown that the energy density follows a power law of d -2 (d is the observation distance) in the far field independent of the size and material of the sphere. The power law in the near field is strongly dependent on the material, size parameter, and the ratio (a is the sphere radius). In the near field, the energy density follows a power law of d -6 when and (similar to an electric point dipole).With increasing X or decreasing , the contribution of multipoles to the energy density increases resulting in an increase in the power of d until the power law converges to that for a semi-infinite medium (d -2.5 , d -0.5 , and d -3.5 for silicon carbide, silicon and tungsten, respectively, in the intermediate near field, and d -3.5 , d -3.5 , and d -2.5 for silicon carbide, silicon and tungsten,
Silicon carbide (SiC) supports surface phonons in the infrared region of the electromagnetic spectrum where these modes can be thermally emitted. Additionally, the magnitude, spectrum, and direction of thermal radiation from SiC can be controlled by engineering this material at the sub-wavelength scale. For these reasons, SiC nanopillars are of high interest for thermal-radiation tuning. So far, theoretical and experimental studies of thermal emission from SiC nanopillars have been limited to long-pitch arrays with a microscale interpillar spacing. It is not clear how far-field thermal emission from SiC nanopillars is affected when the interparticle spacing reduces to the nanometer scale, where the near-field interaction between adjacent nanopillars arises and the array becomes zero order. In this Letter, we study physical mechanisms of far-field thermal radiation from zero-order arrays of silicon-carbide nanopillars with a nanoscale interpillar spacing. We show that the increased volume of thermal emitters and thermal radiation of the hybrid waveguide-surface-phonon-polariton mode from zero-order arrays increase the spectral emissivity of silicon carbide to values as large as 1 for a wide range of angles. The enhanced, dispersion-less thermal emission from a zero-order SiC array of nano-frustums with an optimized interspacing of 300βnm is experimentally demonstrated. Our study provides insight into thermal radiation from dense nanostructures and has significant implications for thermal management of electronic devices and energy harvesting applications.
With increasing market awareness for fuel efficient vehicles, automotive manufacturers are rapidly adopting various hybrid electric configurations (HEVs) to a wider range of passenger vehicles. There are three major HEV configurations depending on the connection between the components that define the energy flow routes and control ports: series, parallel and series-parallel hybrid. Each configuration includes variety of power-transmission patterns. Choosing the right pattern has been always the most important decision in design process of HEV. This paper presents an introduction to hybrid electric vehicles, the commonly used configurations of the powertrain and finally the selection methodology. This methodology could be used by designers to choose the best power-transmission architecture in design processes of a hybrid sedan car with given specification. The expert choice software is used in selection process. The software is programmed based on AHP method. AHP is a structured method which is used for choosing between several options. The introduced method in this article could be used by designers in designing hybrid electric vehicles in all ranges of hybridization.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citationsβcitations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright Β© 2024 scite LLC. All rights reserved.
Made with π for researchers
Part of the Research Solutions Family.