Selective Emission Properties and vdW Energy of Micro/Nano-Sized Spherical Shapes

2016 ◽  
Author(s):  
Alok Ghanekar ◽  
Yi Zheng ◽  
Weixing Zhang ◽  
Zongqin Zhang
Keyword(s):  
Surface Energy ◽  
Radiative Heat ◽  
Near Field ◽  
Van Der Waals ◽  
Radiative Energy ◽  
Curved Surfaces ◽  
Flat Plates ◽  
Size Dependent ◽  
The Past ◽  
Single Sphere

Near-field thermal radiation and van der Waal force between flat plates and curved surfaces have been probed in the past; however the peculiarities of radiative heat transfer and van der Waals stress due to fluctuations of electromagnetic fields for micro/nano-sized spherical objects have not been studied in great details. We demonstrate how fluctuational electrodynamics can be used to determine emissivity and van der Waals contribution to surface energy for various spherical shapes in a homogeneous and isotropic medium. The dyadic Green’s function formalism of radiative energy and fluctuation-induced van der Waals stress for different spherical configurations has been developed. We present the calculations for a single sphere, a bubble, a spherical shell and a coated sphere. We observe that emission spectrum ofmicro/nanoscale spheres displays several sharp peaks as the size of object reduces. Our calculations indicate that surface energy becomes size dependent (r-3) due to van der Waals phenomena for small radii.

Dispersive Properties of Mesoporous Gold: van der Waals and Near-Field Radiative Heat Interactions

2017 ◽  
Vol 121 (22) ◽  
pp. 12392-12397 ◽  
Author(s):  
E. Y. Santiago ◽  
J. E. Peréz-Rodríguez ◽  
Raul Esquivel-Sirvent
Keyword(s):  
Radiative Heat ◽  
Near Field ◽  
Van Der Waals

scholarly journals Enhancing radiative energy transfer through thermal extraction

Nanophotonics ◽  
2016 ◽  
Vol 5 (1) ◽  
pp. 22-30 ◽  
Author(s):  
Yixuan Tan ◽  
Baoan Liu ◽  
Sheng Shen ◽  
Zongfu Yu
Keyword(s):  
Thermal Radiation ◽  
Radiative Heat ◽  
Near Field ◽  
Light Output ◽  
Radiative Energy ◽  
Field Energy ◽  
Far Field ◽  
Thermal Extraction ◽  
Field Radiation ◽  
Boltzmann Law

Abstract Thermal radiation plays an increasingly important role in many emerging energy technologies, such as thermophotovoltaics, passive radiative cooling and wearable cooling clothes [1]. One of the fundamental constraints in thermal radiation is the Stefan-Boltzmann law, which limits the maximum power of far-field radiation to P0 = σT4S, where σ is the Boltzmann constant, S and T are the area and the temperature of the emitter, respectively (Fig. 1a). In order to overcome this limit, it has been shown that near-field radiations could have an energy density that is orders of magnitude greater than the Stefan-Boltzmann law [2-7]. Unfortunately, such near-field radiation transfer is spatially confined and cannot carry radiative heat to the far field. Recently, a new concept of thermal extraction was proposed [8] to enhance far-field thermal emission, which, conceptually, operates on a principle similar to oil immersion lenses and light extraction in light-emitting diodes using solid immersion lens to increase light output [62].Thermal extraction allows a blackbody to radiate more energy to the far field than the apparent limit of the Stefan-Boltzmann law without breaking the second law of thermodynamics.Thermal extraction works by using a specially designed thermal extractor to convert and guide the near-field energy to the far field, as shown in Fig. 1b. The same blackbody as shown in Fig. 1a is placed closely below the thermal extractor with a spacing smaller than the thermal wavelength. The near-field coupling transfers radiative energy with a density greater than σT4. The thermal extractor, made from transparent and high-index or structured materials, does not emit or absorb any radiation. It transforms the near-field energy and sends it toward the far field. As a result, the total amount of far-field radiative heat dissipated by the same blackbody is greatly enhanced above SσT4, where S is the area of the emitter. This paper will review the progress in thermal extraction. It is organized as follows. In Section 1, we will discuss the theory of thermal extraction [8]. In Section 2, we review an experimental implementation based on natural materials as the thermal extractor [8]. Lastly, in Section 3, we review the experiment that uses structured metamaterials as thermal extractors to enhance optical density of states and far-field emission [9].

Casimir Friction and Near-field Radiative Heat Transfer in Graphene Structures

2017 ◽  
Vol 72 (2) ◽  
pp. 171-180 ◽  
Author(s):  
A.I. Volokitin
Keyword(s):  
Heat Transfer ◽  
Energy Transfer ◽  
Transfer Coefficient ◽  
Graphene Sheet ◽  
Drift Velocity ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Near Field ◽  
Radiative Energy ◽  
Phonon Polaritons

AbstractThe dependence of the Casimir friction force between a graphene sheet and a (amorphous) SiO2 substrate on the drift velocity of the electrons in the graphene sheet is studied. It is shown that the Casimir friction is strongly enhanced for the drift velocity above the threshold velocity when the friction is determined by the resonant excitation of the surface phonon–polaritons in the SiO2 substrate and the electron–hole pairs in graphene. The theory agrees well with the experimental data for the current–voltage dependence for unsuspended graphene on the SiO2 substrate. The theories of the Casimir friction and the near-field radiative energy transfer are used to study the heat generation and dissipation in graphene due to the interaction with phonon–polaritons in the (amorphous) SiO2 substrate and acoustic phonons in graphene. For suspended graphene, the energy transfer coefficient at nanoscale gap is ~ three orders of magnitude larger than the radiative heat transfer coefficient of the blackbody radiation limit.

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